Geological evidence about climate change: has there ever been a period with a rate of climate change as great as it is today? Most statistics about climate change are based on climate data over the last 150 year (as long as records have been kept). This seems irrelevant in terms of the geological time scale of temperature variation on the earth.

In the last 400 million years, has there ever been a 200-year interval during which the rate of climate change was as great as it is today?

Quick answer: yes.

But please read the following comments and explanations:

Most statistics about climate change are not based only in the 150 years of instrumental records. We have many good temperature proxies that go back between a millennia and 70 million years. Among them: tree rings, growth bands in corals, layered marine sediments, bog and lake sediments, stalagmites and stalactites, ice cores (800,000+ years), and isotopic composition of shells of single-cell organism called foraminifera. This last one can be used to estimate the temperature of the deep ocean as far back as 70 million years.
Although, the interpretation of the isotopic composition could be tricky, the caveats do not change the general picture presented by this long term temperature record. Here is a reconstruction of temperature based on foraminifera shells.

You can see that there were long periods of time with temperatures much higher than today. However, when it come to the rate of change this record doesn't have the resolution to answer your question.
As a first remark, note that we don't have a reliable temperature record going 400 million years back, and for the ones that do extend multiple million years, the resolution is not good enough to see quick climate change events as the one we are experiencing now.

However, we don't need to go that far back to find climatic changes greater than the one we are experiencing today. Such changes are actually visible in the 800,000 years records recovered from antarctic ice cores. And actually, the best examples come from high-resolution Greenland ice cores that go only about 110,000 years into the past.

One of the most studied quick climate changes is the one after the Younger Dryas about 12,000 years ago. Considering changes in the chemical composition of the atmosphere, and proxies of temperature, the data suggest that climate change after the Younger Dryas and other previous ones were more dramatic than the cumulative changes in the last 200 years. And such dramatic changes happened in periods as short as 40 years. The end of the Younger Dryas was associated to changes in temperature of 8 °C or maybe up to 15°C regionally, accompanied by two-fold changes in precipitation and methane concentrations (reference 1, reference 2)

Unfortunately the second reference (a Nature paper) is behind a paywall so I'll add here figure 4, the most relevant to this question.

You can see how fast are the changes in methane concentrations and $\delta^{18}O$. As a rough reference, a change of one unit in $\delta^{18}O$ is equivalent to a change in temperature of 2 °C, therefore the big jump in the figure is about 10°C.

Now I could argue that given that agriculture appeared just after that change (~12,000 years ago). When assessing if we have faced in the past a climate changes as dramatic as the one we are observing now you have to focus on what happened after that time. And notably, since then, the climate have been very stable. In fact, the change we are experiencing now is the largest after the invention of agriculture (previous references and this one).

As a corollary, it is important to realize that Earth's climate is much more chaotic and capable of large changes in short periods that what you would think by looking at the written history, and that we have enjoyed a long period of calm that at some point, sooner or later will be followed by changes unprecedented in human history.
The equilibrium we have enjoyed might be a kind of unstable equilibrium, and you might not need a very large perturbation to upset that equilibrium and send the system into a large climatic swing.


Why did Hurricane Harvey have so much lightning associated with it? Hurricane Harvey (Category 4 hurricane, in August 2017) was a prodigious lightning producer when it hit Houston/SE Texas. But I thought hurricanes don't have much lightning (with the eyewall being the only exception), due to tropical cyclones featuring mostly horizontal shear that inhibits the in-cloud charge separation needed for lightning strikes.

The storm and basics:
Here is an animation I got from this NOAA Tweet of the lightning in Harvey hours before landfall:

https://mashable.com/2017/08/31/harvey-weather-satellite-maps-lightning/, where I found the imagery, offers some basic thoughts, including the key concept that:

As with most hurricanes, you'll notice that the most active area of lightning production is well away from the center of the storm.

This may well explain the reason you experienced more lightning if you are in a location nearer Houston, as it was quite far from the hurricane.  Landfall was about 180 miles SW of Houston, and by the time the storm made it near the Houston metro, it was much weaker; maximum sustained winds around the metro were generally only 25-40 mph (see table starting on page 30).

Deeper Look At Causes of Lightning in Tropical Cyclones:
I don't think I've come across horizontal wind shear used as an explanation for the reduced lightning in hurricanes, though that doesn't mean it isn't.  But upon more consideration, I really don't think horizontal wind shear in hurricanes is actually particularly extreme.  Certainly there are higher overall wind speeds than many weather features, but the horizontal gradient generally occurs over the scale of 10s of miles (10s of km) or much more in most of the storm.  Whereas in typical summer thunderstorms, there can quite often be like a 50 mph (75 kph) gradient over just a mile (or even km).  I guess the horizontal shear can be quite big right near the outer and especially inner eyewall edge... but these are such small geographic areas to explain the lack of lightning in the large part of a hurricane.  (Looking at figures 3 and 5 from this paper looking at Hurricanes Ivan and Dennis, it looks like the broad horizontal shear only peaks at like 10 m/s over a distance of 5 km, or about 7 mph per mile in Ivan, and less in Dennis.  I don't think that's a big amount really?)
And you may know that hurricanes tend to have low vertical wind shear.
So what is the cause of reduced lightning in hurricanes?
The paper Reflectivity, Ice Scattering, and Lightning Characteristics of Hurricane Eyewalls and Rainbands. Part I: Quantitative Description by Cecil et al. from 2002 summarized it as:

Despite extreme horizontal wind speeds, the vertical motions
encountered in tropical cyclones are typically rather modest
(Jorgensen et al. 1985; Black et al. 1996), with magnitudes similar to
those found in ordinary tropical oceanic convection. Convective
systems over the tropical oceans produce weaker vertical motions than
their continental counterparts (LeMone and Zipser 1980; Jorgensen and
LeMone 1989; Lucas et al. 1994; Igau et al. 1999). These vertical
motions are normally too weak to suspend large ice particles or
supercooled raindrops above the melting level.

This summary of how lightning forms on a course website by Dr. David Newman at University of Alaska and this NOAA page help explain the main theory on lightning formation.  And Observations of the Distribution of Ice in Hurricanes by Black and Hallett from 1985 helps indicate what is missing in hurricanes.
Basically it looks like with a weaker updraft, when moisture reaches the height of freezing, it "gathers" into the larger ice (graupel and hail) that falls relatively shortly up more, since it rises so slowly.
And so you there isn't much supercooled water (and the smaller hail\graupel grows more slowly when it collides and so falls more slowly as well)
Whereas with a stronger updraft, the more rapid rising motion means the moisture gets higher up before attaining hail/graupel... and so leaving a larger layer with just supercooled water\ice crystals below.  And that supercooled water is the vital thing, causing the heat release when freezing to falling ice.  And so you have different particles with different charges.
So only areas of stronger rising motion can form those better depths of "unglaciated" areas with supercooled water.  How do you get more rising motion?

Pockets of more unstable air (hotter moist air near the ground or cooler air aloft).  These will typically only be found at far extents from the storm, as nearer the center you tend to have moistened and well mixed the entire region.  Sometimes well placed dry air intrusions into a storm may offer a bit of help.
Additional forced rising by converging air below... this can be big features like eyewall replacement cycles, shear tilting, or frictional convergence as a storm makes landfall or more localized embedded supercells.

The answer for Harvey is probably all of the above.  Places like Houston were first in the further extents of the storm the early days and so were able to see the more typical fluctuations of strong rising updrafts and stronger sinking downdrafts more typical of normal thunderstorm convection and the outer rainbands in tropical cyclones.  And then had a storm seeing important structural changes by the time it moved nearer Houston (as marked by the significant tornado outbreak)
And areas nearer the center of Harvey saw rapid intensification (indicating there was more instability nearer the storm center still), eyewall replacement, plus the usual frictional convergence at landfall all favoring a bit of an uptick in lightning.  Harvey may well have not been too different from most landfalling hurricanes, but had the benefit of rapid intensification to help lightning production some... and it was dark so it could be seen more!


Could someone tell me what this stone might be It is 9 1/2 inches by 3 1/2 inches and weighs about 5 lbs. it was at this house in Florida when we bought it. It has a white 1/4 inch crust and the interior color looks somewhat topaz.

Most likely some form of chalcedony, not knowing where you found it, I'd call it flint, a form of chert.


When does an island with isthmus become a peninsula? I'm currently on holiday in Indonesia. In my travel guide I was reading about the island Samosir, which I'm visiting in a few days. I read that the island, which is located in lake Toba, is connected to the main island of Sumatra by an isthmus. This got me wondering whether this wouldn't technically make Samosir island a peninsula.

So my question is: what (if anything) is the technical difference between a peninsula and an island connected to its parent landmass by an isthmus?

I think the naming difference is largely qualitative and even arbitrary in some cases. There are lots of 'islands' that are technically connected to a larger landmass by an isthmus of some sort, which would make them peninsulas technically, and not islands.

If you take the definition of a peninsula to be a body of land surrounded by water on three sides, then yes, the island in question could technically be called a peninsula.

Local names of landforms are often linked to cultural or historic influences, just as much as they are to their technical description. There's no 'threshold' of isthmus-width (as far as I'm aware), where once crossed, a peninsula-like island becomes an island-like peninsula . If there was it would be entirely arbitrary.

As an interesting aside, the Isle of Harris in Scotland is not only not an island (there's an isthmus connecting part of it to a larger landmass) but even the isthmus part is not used to define the limit of the island, which occurs at some seemingly arbitrary point on the larger landmass! (see the map in the link to see what I mean)

https://en.wikipedia.org/wiki/Harris,_Scotland


Radon is a naturally occurring radioactive gas. How does this work? Radioactive rocks can release a gas called radon when they decay, which can build up in the basements of buildings with serious effects on people's health.

Does anybody have information on how radon is produce naturally in nature? How do these rock’s become radioactively charged?
Are these rocks common? Pictures or examples?

Radon (more specifically Radon-222) is produced in the decay chain of Uranium-238.   Radon-223 is also produced by the decay chain of Uranium-235 and Radon-220 is produced by the decay chain of Thorium-232 but both Radon-223 and Radon-220 have half-lives of less than a minute, so they almost never reach the atmosphere where they can be breathed in because they mostly form underground and they decay too quickly to reach the atmosphere.

Radon is unusual in that it's the only noble gas along the 4 primary decay chains and only the Uranium to Lead chain produces Radon-222 which has half life long enough to reach the atmosphere and get breathed in.

More on decay chains here and here.

Uranium-238 has half life of about 4.5 billion years, so about half the Uranium-238 that was present when the Earth formed is still here.  It decays very slowly, which is why it's not dangerous to be around Uranium in it's natural form.  (though if somebody hands you a block of it, you might still want to wash your hands after touching it - then call national security) . . . but I digress.

Radon-222 has a very short half life of 3.8 days, so while the Uranium that produces it decays very slowly, the Radon is highly radioactive and it decays (into other radioactive elements) quite rapidly.   If you had a sample of Radon-222 for example, in less than a month, 99% of your sample would be gone.

Because it forms slowly and decays quickly it never collects beyond a very trace concentration and it continuously needs to be regenerated.

Houses with a Radon problem need to be continuously ventilated because of that regeneration.  At least/about two or three times a day I would think (see comment directly below, once a day may be sufficient), but it's worth pointing out that the Radon in houses is so faint that it takes months, if not years, for any kind of health problems to arise.   It's kind of a weird thing.  It's not dangerous at all to walk through a house with unsafe Radon levels, similar to how it's not dangerous to visit Chernobyl.   It's just not a good idea to live there.

Radon is also likely to only be a problem in poorly ventilated houses, (basement's especially, because the heavy gas tends to settle) but a good ventilation system should make any house safe.  And it's more common in specific areas.

There's the problem of keeping the house warm in winter and maintaining ventilation, because ventilation does need to be maintained.  Houses can be also built above ground to reduce exposure.

As a general rule, it's the ingestion, either breathing or swallowing of radioactive material that's most dangerous.  That's why it's a good idea to put on a gas mask to prevent breathing in any radioactive dust or fallout (though a gas mask won't keep gas like Radon out).   And it's a good idea to leave your clothes in a separate changing room and shower thoroughly if exposed or walking through radioactive fallout - that has nothing to do with your question, just putting it out there.   Also the opposite applies if there's radiation outside from a nuclear accident or bomb- close all windows and try to keep ventilation as close to zero as possible, at least for a day or so until you get instruction on the levels, but . . . I digress.   Point is, because Radon is easily breathed in, it's quite toxic even in very small amounts.   At the same time, the Radon concentration inside houses with a radon problem is so small, that it still takes months if not years of exposure to lead to problems.

That's why Geiger-counters aren't used to test for Radon.  There's too little radiation.  You need specific Radon detectors.

  Are these rocks common?

Yes, and no.   Because the gas comes from Uranium, (and mostly from underground), Uranium isn't exactly common but it's not super-rare either.

  How do these rock’s become radioactively charged?

This was covered above, but Uranium, in small amounts, is in lots of different places.   The Rocks were always (mildly) radioactive.

  Pictures or examples?

To my knowledge, pictures or examples don't do any good because trace amounts of Uranium in rocks doesn't look any different.  Besides, most of the Uranium is underground.   You have to rely on Radon testing and look at locations where Radon is more of a problem.   If you live and work above the first floor, and not near a mine or massive dig-site, you probably have little to worry about.   If you live in a basement, you should have it checked out.

On the process

The Uranium or U-238 goes through several steps in it's decay and this chain is only the most common outcome.  Part of the problem with Radon, is if you breath it in, and don't breath it out, it becomes Polonium and goes through a few other steps.  In high enough concentration, Radon is extremely toxic.  From rocks, the concentration that's likely to form in a house is usually low enough that harmful exposure takes months or years.


Decomposition of variables in horizontal and vertical modes I have a query regarding the practical applicability of variable separable method. Usually we decompose the variables w.r.t components corresponding to different dimensions, this method is used to solve a differential equation analytically. When it comes to the practical usage, we are often provided already with the solution in form of model output. Is it possible to decompose them along their dimensions? For example I can write the zonal velocity as
              U(x, y, z, t) = uv(z) * uh(x,  y,  t)

Will this decomposition be unique? I am clueless because it just seems to be a matrix multiplication. I wonder how would be the form of those matrices. Is it possible to obtain uv and uh from the data variable using any software tool?
Edit: An example of such a decomposition is provided here at page number 7 (equation 2.6). I wonder if it is possible to obtain the decomposed RHS values practically from a variable.
Moreover I often see a PDE associated with the decomposition which is absolutely logical. The equation is solved analytically by substituting the decomposed variables and different software tools are able to plot the analytical solution. The situation is little different in the study attached herewith. I wonder how to obtain the decomposed values if I am not getting any way to solve it analytically.

Multiplicative decomposition as defined in the post is often called factorization. It is not always possible to achieve an exact factorization. There would be some residual difference that we could denote as eps(x, y, z, t).

U(x, y, z, t) = uv(z) * uh(x,  y,  t) + eps(x, y, z, t)

Such a decomposition is not unique, however you may choose a pair of functions that minimizes the value of eps(x, y, z, t) according to some metric.

For further reading consider the description of sklearn Non-negative matrix factorization function.


Composition of Martian Crust Does the composition of the crust of Mars roughly correspond to that of the crust of Earth. That is, is the elemental abundance in decreasing order silicon, oxygen, aluminum, etc.?

The most abundant elements are:

Element  Approximate % by weight

Oxygen        46.6
Silicon       27.7
Aluminum       8.1
Iron           5.0
Calcium        3.6
Sodium         2.8
Potassium      2.6
Magnesium      2.1
All others     1.5

Source:http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/elabund.html

Based on data from a number of NASA and ESA spacecraft and rovers,
(Fine summary on wikipedia: https://en.wikipedia.org/wiki/Composition_of_Mars). The four top elements are most likely the same. They are roughly the same on Mars and Earth and may be in the basic proportions

Oxygen
Silicon
Aluminum
Iron

I would expect at some point that the relative abundance of elements on Mars to deviate from that on Earth based on the following differences:

Earth and Mars were most likely formed at two very different distances from the center of our solar system.  This may have significantly affected the elemental abundances between the two planets.
Earth has had significant amounts of water since from very early in its history, as recorded by some of the oldest rocks on Earth which are meta-sedimentary deposits in Australia.
We do not known how much water has ever been on Mars. Mars is currently very dry.  Water plays a big role in element distribution on Earth and my guess is water will have played a smaller role on Mars.
Lastly, I am becoming convinced that biologic activity has also significantly affected element distribution on Earth.  Bacteria/Archaea have been found in deep rocks in South African gold mines, which is remarkable. Bacteria and Archaea may play a larger role in various geological processes than traditionally thought.  The Mantle is no longer viewed has dry and sterile.
Life on Mars (even as  Bacteria/Archaea) is yet to verified.


Relationship Between Ratio of Atmospheric Gases and Ocean Gases A version of this question was posted in Chemistry SE and Worldbuilding SE but I've been told it wasn't appropriate to either SE. I was told to give this SE a chance. If you think it doesn't belong on this SE please let me know how to appropriately edit or otherwise another SE to try.

Note: This problem comes from my interest in exoplanet sciences but is applicable to earth sciences.

Something that's unclear to me is the exact relationship between gases within an atmosphere and the concentration of those gases within the bodies of water under that atmosphere (like an ocean).

For example, the solubility of $CO_2$ at $298K$ and 1 bar of atmospheric pressure is ≈ 1.496 g/L in water. My understanding is that number indicates how much $CO_2$ can be dissolved within water before the water is saturated with $CO_2$ and won't accept any more. However this doesn't tell me what the concentration of $CO_2$ would be under given conditions, it just sets a maximum cap. So 1.496 g/L of $CO_2$ might be dissolved in water, but it could be much much less.

Key Question: What are the calculations I need to go through to figure out the amount (total and ratios) of gases in both a planet's oceans and atmosphere assuming I know either:

The total amount of gases within the ocean/atmosphere system, or...
The amount of gases present in the atmosphere but not the corresponding amount present in the waters.

I want to be able to figure out all the ratios of gases within an atmosphere and dissolved in a planet's waters. Ball-parking is fine if that's the best I can do.

I know this is probably a very complex topic, so if it's helpful you could look at the idealized  earth situation I've outlined (below) and rift off those numbers. Not necessary, but there if you need it.

You could also take the approach of looking at two gases with very different solubility in water, like $CH_4$ than $CO_2$ and look at what would happen to the ratios if there was a heck of a lot more of the less-soluble gas (Methane in this case) in the system than the more soluble gas.

Whatever approach you take, I'd appreciate any insight you can provide. What I really want to learn is both general principles as well as how to establish those principles in actual calculations.

Scenario: If useful refer to these numbers

Assume uniform temperatures at water surface. Assume no minerals dissolved in water.

SURFACE (Idealized Earth)

Total Surface Area: 510 million $km^2$
Water Surface Area: 361 million $km^2$
$15C$ Uniform Surface Temperature

ATMOSPHERE (Idealized Earth)

By Volume: 79% Nitrogen, 20.95% Oxygen, 0.049% Carbon Dioxide, 0.001% Methane
Surface Pressure: $1$bar

OCEAN (Idealized Earth)

Water Ocean (What should be the corresponding dissolved gases?)
Volume: $1.4$ billion $km^3$

Bonus: What would change if we lowered/increased atmospheric pressure and/or lowered/raised temperature?

The law that governs the pressure of gas at equilibrium over a dissolved liquid is called Henry's Law. Note, the equilibrium assumption, as there is some time dependence. That is, if you start with no dissolved gas in pure water, then in a relatively short amount of time, the amount of dissolved gas will be less than equilibrium.
Let's talk in abstractions. Henry's law's temperature dependence resembles the Clausius-Clapeyeron equation, so we can draw some parallels. From the Wikipedia link, for a given gas, the Henry's law constant is $$H(T)=H(T_0)\exp\left[-\frac{\Delta K}{R}\left(T^{-1}-T_0^{-1}\right)\right]$$ .$-\frac{\Delta K}{R}$ is Wikipedia's version of $-\frac{\Delta_{sol} H}{R}$, but I used $K$ to not cause confusion. For pure water, this link shows the solubility of different gases at different temperatures, but most relevant is the temperature at 0$^\circ$C (that is, it gives $H(T_0)$).
But all of this doesn't answer the two questions that your question boils down to.

Raising the temperature decreases the solubility of a gas.
If the pressure increases, then the amount of gas that can be dissolved increases per Dalton's Law. If the system is not in equilibrium, then the amount of solute will increase in proportion to Henry's Law.


When was the last time there was a landlocked body of water bigger than the Caspian? Was it the Mediterranean before it dried into small lakes? What was the biggest one before that?

The Tethys, which was previously an ocean, became landlocked by the Indian subcontinent to form a massive body of water before the Indian plate collided with the Euarasian to form the Himalayas (about 250-400 Ma).

I don't see any visuals on the Tethys as a sea (as opposed to when it was an ocean) widely disseminated on the web. Here's an approximate diagram from my memory of a textbook:


How to distinguish between Altocumulus, Stratocumulus and Cumulus clouds? There are four different categories of clouds. High clouds, medium altitude clouds, lower clouds, and vertical tall clouds. They are broken down into ten genuses of clouds: Cirrus, Cirrocumulus, Cirrostratus, Altocumulus, Altostratus, Stratocumulus, Cumulus, Stratus, Cumulonimbus, and Nimbostratus.

Additionally there are 14 species, 9 types, and 9 additional phenomenons like Virga or Mammatus, but these are not really important in my question.

I find it troublesome to distinguish the Altocumulus, Stratocumulus and Cumulus clouds from each other. The hardest to distinguish in my opinion are the Stratocumulus and Altocumulus clouds. Even though I know, Ac are higher clouds than Sc, it is most of the time hard for me.

Can anyone point out any differences that would help me distinguish these genuses of clouds?

You are not alone. Allmost everyone has difficulty differentiating Ac from Sc because, apart from the obvious low clouds, you can't accurately discern a cloud's height purely from looking at it. For that you need a 'ceilometer', which is a vertical beam of light reflected off the cloud-base. Not many met sites have this.


Spatial extent and predictability of various hazards. My question concerns the following three hazards: earthquakes, hurricanes and drought.

In terms of spatial extent (wide spread, limited), I believe that earthquakes generally have the most limited spatial extent of the three, followed by hurricanes. However, I am unsure about droughts. I assume that they have the largest spatial extent of the three, but would anyone be able to give an explanation as to why?

With regard to their predictability (hazard assessment), I would say that the order (from most predictable to least) would be:

Hurricanes
Drought
Earthquakes

Hurricanes as past trends can be assessed and there are specific conditions that are required for a hurricane to form (e.g. between 5, 20 degrees from equator).

I am less sure about prediction methods for droughts, but I assume that precipitation levels can be monitored, etc.

Lastly, I am aware that historic trends can be assessed for earthquakes and the general areas that will be affected can be predicted, however it is difficult to predict where the earthquake will occur along the fault line and the magnitude (I am aware that there are numerous questions on the predictability of earthquakes)

I would love it if you could share your thoughts in terms of how you would order the hazards and why.

Drought is not comparable to earthquakes and hurricanes because of the difference in time scale involved. We can generally consider earthquakes and hurricanes to be discrete events at a point in time. Drought, however, has a significant and variable time component. For example, you might consider a year of severely below average rainfall to be a drought but there are also multi-year droughts with prolonged periods of low rainfall. Descriptively, you can plot the average rainfall for an area along with the cumulative deviation from the average to see the trends. Even that should be used with caution - one year of very high rainfall may have a big effect on the deviation from the mean but won't really help rain-fed agriculture in subsequent low years. Here is a guide to the different definitions of drought.

The probability of a hurricane hitting the eastern United States in the next decade probably approaches 1.0 but to narrow that down to specific cities is more difficult. Once one has formed, the meteorologists are getting very good at predicting where it will make landfall. In between, the probability of a hurricane striking a particular city in a given year is low.

With regards to earthquakes, there are many known faults where measurements indicate a high probability for a large earthquake. However, the timing may be within hundreds or thousands of years. We can predict where but not when.

These are all different ways of looking at prediction that illustrate the considerations in how we think about 'prediction'. Ranking them is comparing apples to oranges.


What percent of volcanoes are glaciated? I have not been able to find an estimate of how many known volcanoes host perennial ice masses, and it would be very useful to me. Does anyone know of any attempts to do this?

21.7%, by my calculations (338 / 1556 holocene-active volcanoes). I calculated perennial snow by combining 6 weeks of MOD10A2 data from winter and summer weeks in 2014 to figure out which pixels had snow both in the summer and the winter. My source code for that is available as a gist (an older version accidentally classified cloud as snow; that's been fixed). Then I checked if these pixels fell within 10km of the volcanoes in the Smithsonian Institution's Global Volcanism Database. I also plotted the woefully incomplete Global Land Ice Measurements from Space glacier polygons.

There are clearly a few false-positives on ocean islands... I think this is due to MOD10A2 marking choppy surf as snow. Looking into that. I intend to publish this and will put a reference here if it is published.

Here's what the map looks like for part of Alaska:

And the whole world:


Why is carbon dioxide the gold standard in greenhouse emissions - and not nitrous oxide? I admit that this is not a genuinely earth sience question, but since there is no stack exchange site genuinely devoted to general ecology, I dare to ask it here:

From a table in the German Wikipedia article on emissions trading I've learned that the global warming potential of nitrous oxide is 298 times as high as that of carbon dioxide, and that it makes 7.9% of the humans caused greenhouse gases:

Given these numbers nitrous oxide seems to contribute roughly 30 times more heavily to climate change than carbon dioxide does.

Why is nevertheless carbon dioxide the gold standard of greenhouse gases and humans caused climate change?

There isn't enough nitrous oxide in the atmosphere to make a major contribution to global warming, which in some ways is a pity, because we'd all bee in a much jollier mood if there was (N2O is sometimes known as laughing gas). It also depletes the ozone layer if it gets up that high, though depleting ozone at ground level, where it is harmful, is a good thing. Compared to N2O, there are vast quantities of CO2 in the atmosphere, enough to create millions of tons of wood and other plant materials every year. The whereabouts of N2O in the atmosphere, whether it is high up or low down, probably has some bearing on the matter.


Is it true that aquaponics yield crops with a lower nutritional value than soil-agriculture? I read this article, in which a person claims that Aquaponics bring crop quality down by having more water than actual nutritional value.

I have read many other sources that say the opposite. Can anyone guide me towards the research that says that aquaponics/hydroponics yields crops with lower nutritional value? I couldn't find open access peer reviewed articles that say as much, but maybe I left a stone unturned.

First look at the article, is cites no sources and is not written by an an expert. It is written without peer review and does not seem to understand how to measure nutritional content (brix is only a measure of sugar not minerals) or what controlled conditions are. No methodology for collection, type of hydroponics, sample size, or anything else is given, this is important becasue many many thing unrelated to the farming method can effect Brix. So you can safely ignore the unscientific claim of the article and go with scientific ones, which show no difference when tested.

First always look at the source of a claim and when in doubt search google scholar first.

This is clearly editorial click bait.


Why does Australia have extensive uranium ore deposits? According to the World Nuclear Energy page about Australia's uranium deposits, the continent's

  known uranium resources are the world's largest – 31% of the world total.

Of which

  In 2013 Australia produced 7488 tonnes of U3O8. It is the
  world's third-ranking producer, behind Kazakhstan and Canada.

The deposits are found across the Australian continent, within different geological regions of different ages (e.g. most of the deposits in the eastern part of the continent are considerably younger than those in the west).  The main known deposits are shown in the map below, by Geoscience Australia:

Why does Australia have extensive uranium ore deposits?

Related to this question is the recent question Did an impact crater influence the formation of uranium deposits in South Australia, and related questions and answers, Why is there Uranium in Earth's Crust? and How much Uranium is there in the Earth's Crust? - this question is specific to the relatively high abundance of uranium occurring in the Australian landmass.

An aptly named webpage from GeoScience Australia: Why Australia has so much uranium provides some insight as to some of the reasons behind the Australian continental relative enrichment in uranium.

Consider the following map from the GeoScience webpage:

One link that is stated on the website is that in regards to major uranium deposits"

  observations support the conclusion that the large number of uranium deposits and prospects across Australia reflects the extensive emplacement of uranium-enriched felsic rocks in three main periods of igneous activity. While some uranium deposits appear to have formed during these widespread thermal events, most formed from uranium-enriched source rocks by subsequent low-temperature processes.

These 3 main periods occur:

Late Archaean (2.69-2.65 Ga)
the Palaeo-Mesoproterozoic. (~1.9-1.5 Ga)
and a bit younger in eastern deposits, the Silurian to the Permian (0.43-0.25 Ga)

The last point in bold above is elaborated further by the website, that uranium mineralisation being younger than the related intrusive igneous rocks.  Particularly evidenced by deposits found in calcrete, sandstone and unconformities:

  appear to have formed as a result of uranium mobilisation from older uranium-enriched source rocks under low-temperature oxidising conditions, and precipitation by redox reactions. The high-grade deposits are likely to reflect relatively more efficient oxidation-reduction systems.


How are the Scala dei Turchi staircases formed? The Scala dei Turchi i (Italian: "Stair of the Turks") is a rocky cliff on the coast of Realmonte in Italy:

https://en.wikipedia.org/wiki/Scala_dei_Turchi#/media/File:Scala_dei_Turchi_panorama.jpg

How is the shape of a staircase formed?

Could it be some sort of stretching process?

There's no need to invoke stretching here. This is just a simple case of dipping sedimentary beds which have been eroded by the sea.

The stepped geometry may be caused by small variations in the hardness of the beds such that the harder beds weather out more prominently and create the steps.

Alternatively, at least some of the larger steps may be wave cut terraces formed during periods of stable sea level. In the background on the left of the picture you can see two large terraces separated by a ramp which look very much like wave cut terraces. Such terraces are well known from central Greece, where they have been uplifted by activity on faults and I would speculate that a similar process has occurred here.


How large is the area covered by coordinates XX°YY'ZZ"N/XX°YY'ZZ"E? As stated in the title, I wonder how large the area covered by certain coordinates actually is, when they have the accuracy XX°YY'ZZ", for example:

51°26'02"N, 07°20'04"E

How can this be calculated?

This is a coordinate, a single point. No area or distance can be calculated from that, sorry ...

https://en.wikipedia.org/wiki/Geographic_coordinate_system

The length of one arcsecond depends on the latitude. The Wikipedia article explains it quite well. Distances between two coordinates can be calculated via the great circle distance. Calculating areas on earth's surface is more involved, since they require a projection into 2D.


How much plastic settles to the bottom of the oceans each year? This article says that 5 to 13 million metric tons of plastic go into the ocean every year.  In the study At what point do floating plastics sink?, they give an estimate of the weight needed to sink plastics.  They reference the paper Assessing marine debris in deep seafloor habitats off California, which assesses the amount of plastic debris that has settled to the bottom of the ocean off the coast of California.  Given this information as a starting point... How much plastic settles to the bottom of the oceans each year?

About 18.2 million tons sink to the ocean floor.

Every year, an astonishing 260 million tons of plastic waste is produced, and about 10% of it ends up in the ocean. Over time, roughly 70% of the plastic that ends up in the ocean sinks to the ocean floor.

Therefore 18.2 million tons of plastic waste end up on the ocean floor.

I used this article for my numbers.


How do mantle plumes travel from the core of Earth to the crust? As mantle plumes begin in the core and move towards the crust, I would have thought that the heat in the mantle plume would disperse to the surrounding mantle, and the plume would cease to exist by the time it reaches the crust, a large distance away.

So how is the mantle plume able to survive with such a localized trajectory on its way from the core of Earth to the crust?

The high values obtained when estimating the Rayleigh number for the mantle indicates that convection there is vigorous, and that convection is responsible for almost all the heat transported from the deep interior to the surface. Similar systems set up in the laboratory can develop 'plume-like' patterns of convective flow, and so mantle plumes are a physically plausible model of mantle convection too.


Good Open source alternatives to SeisImager & RES2DINV? Are there any good open source (Linux) alternatives of SeisImager which includes Pickwin and Plotrefa and file formats are .sg2?

Same question for RES2DINV?

Actually, there are plenty of alternative DC Inversion software;

I hate using res2dinv; unfortunately it's relatively easy to get into. I would have much preferred ZondRes2D for it's user experience.

Look up DC2DInvRes (Resistivity.net), and BERT by Thomas Gunther. You may need to contact Thomas for Bert codes, however it's all done in Python and easily read.

Here is another one, but in matlab. (http://www.degruyter.com/view/j/acgeo.2015.64.issue-2/acgeo-2015-0071/acgeo-2015-0071.xml)

Here in another, again in matlab.
https://github.com/cageo/Karaoulis-2013


Cloud-to-ground lightning in Florida? I was looking into the odds of getting hit by lightning and ran across this map:

My first thought for this was due to a higher number of thunderstorms in Florida.  However, the map for that doesn't seem to line up:

The midwest clearly has the highest concentration of thunderstorms, yet Florida is the leader in cloud-to-ground lightning.

My question: Why does Florida get so much cloud-to-ground lighting, even though it doesn't have very many severe thunderstorms?

Your map of lighting tells you where thunderstorms occur.  Your second map of watches tells you where a subset of thunderstorms exhibiting severe threats (high winds, large hail or tornadoes).  The type of thunderstorms that frequent Florida are air-mass thunderstorms and generally will not warrant a severe thunderstorm watch.  The storms in the midwest that do get watches are typically of the supercell variety or associated with squall lines or bow echoes.

Your thesis that "The midwest clearly has the highest concentration of thunderstorms" is incorrect.  What your data says is that the midwest has the highest concentration of thunderstorms producing severe weather threats.  This is not the same as concentration of thunderstorms.  All thunderstorms produce lightning (by definition), not all of them are severe.

Convection in Florida is driven by the sea breeze and afternoon storms happen there like clockwork.  These storms produce lightning but no threats that would warrant a severe thunderstorm watch.  These storms last about 45-60 minutes and produce lightning.  This also makes Florida the lightning capital of the US, as the data in your question shows.


Digging depth and heat I have a question about the underground heat at different distances from the core of the Earth.

I was wondering if there was a depth at which you can dig that the decrease in heat (as a result of being lower) and the increase in heat due to the depth that you dug that the loss of heat was the same as the gain in heat.

Here are the assumptions that I am using:

The lower an object is, the cooler the air around it and therefore the cooler the object can become. Cold air tends to sink below heated air. (I'm thinking like a basement is cooler than the top floor during summer without air conditioning).
The deeper you dig towards the centre of the earth, the hotter your surroundings become. (While there may be some initial decrease in temperature, I'm assuming as you dig towards the mantle or core the hotter the ground around you is).

I am holding constant the heat from the sun and atmosphere. Is there a defined depth at which the loss of heat (from falling cool air) = gain in heat (from the heat of the earth)? Does the shape of the hole dug affect the depth at which this occurs?

The heat equilibrium depth will vary for different locations due to:

Differences in geothermal gradient at different locations (heat emitted by rock). It is generally accepted that the global geothermal gradient is between
${25 ^o C/km}$ & ${30 ^o C/km}$. At some locations the gradient can vary between ${15.4 ^o C/km}$ & ${102.6 ^o C/km}$.
The temperature of the air will increase with depth due to
auto-compression of the air (also known as lapse rate). [Environmental Engineering of South African Mines, 1989, pp 403-404]. The increase in dry bulb temperature of air due to auto-compression is ${9.66 ^o C/km}$, if there is no change to the humidity of the air.
Moisture content of the air. The greater the humidity, the greater
the heat in the air.
Ventilation of the hole being dug and how much heat the moving air is
removing from the bottom of the hole.
Temperature of the air entering the hole from the Earth's surface
The presence or absence of other sources of heat such as machinery, electrical equipment, warm water springs entering the hole and warm bodies.
The age of the hole and its exposure to ventilating air. New holes expose fresh warm rock to air in the atmosphere and the air eventually carries away the heat via ventilation. New holes, or new extensions to holes, are warmer/hotter than old holes.

The shape of the hole will be determined more by its function and geotechnical conditions, such as ground stability, than temperature.


How did forests end up covering pyramids? I went to Mexico and the pyramids are covered by vegetation. It's only after archeologists clean them that you can actually see the pyramids. Before that they looked like a natural hill, with soil, trees, ...

How is that possible? I can imagine grass or small weeds growing here and there in between the stones with seeds being disseminated by wind or birds. But how did soil get up there? Whatever 'lucky parts' of soil that got up there should be washed off with gravity, wind, rain, no?

I am an archaeologist and I specialize in the ancient Maya. Here's how it happens:

1: The vast majority of ancient Maya buildings are built using a "core and veneer" technique. The bulk of the building's volume is earth and stone rubble, faced with a veneer of nicely-shaped limestone blocks that are themselves covered by a layer of lime plaster (stucco). The geology of the Yucatan peninsula is almost entirely limestone, so they built with what they had available.

2: Most pyramids have multiple construction phases, with each one adding a new layer of rubble/earthen core and cut stone and stucco veneer. The building gets bigger with each renovation.

3: Following abandonment, strong seasonal rains quickly erode the lime stucco on much of the outermost layer. This eroded stucco is chemically and structurally identical to the eroded bedrock that underlies natural soils in the Maya region, meaning that plants can readily grow on it.

4: The limestone used for cut stone veneers is itself really porous and prone to crack, pit, and erode in most parts of the Maya lowlands. I am constantly seeing small trees growing out of ostensibly solid blocks of limestone--their roots can still get plenty of purchase. As such, trees can easily take hold in the space between blocks and in small imperfections in the stones themselves.

5: As the trees grow (and especially as their roots push or pry out loosened veneer stones), the cut stones from the veneer give way, exposing the earthen/rubble core underneath.

6: Other posters are correct that some topsoil builds up as a result of wind-transported dust and decaying plant matter, but this is a very, very small amount, especially on the steeper upper portion of the building (remember, the buildings become less steep overall as they erode, because what had been on the upper part tumbles down and piles up around the base, reducing the gradient). Instead, most of the "soil" was actually put there by the Maya as part of the final construction phase, covered by a layer of modern humus.

7: It follows that in many parts of the Maya world, what you see when you look at a cleared/restored pyramid is not really what it looked like in its final stage. Instead, it's usually a mix of the last and second-to-last construction phases, both having been subject to varying degrees of erosion, with the last phase usually only preserved toward the bottom and at the very top.


Where/how people find minerals Forever I have seen little shops here and there offer minerals like those crystals and neat shaped rocks of different kinds, turquoise and amethyst and many others and such. But I never really thought about it.

In looking a bit it doesn't seem there is a Home Depot for minerals. That is, there's no giant store that offers tons of minerals of every kind in vast quantities. The biggest collection of minerals I ever saw was this:

All of those tiny fist-sized samples are probably pretty much different types of minerals. So then to scale that to buckets or bins and tractors full of each type, I have never seen.

So it seems that these small shops get the minerals in small quantities from somewhere other than a Home-Depot--like place. That's what I'm wondering about (the first part of the question), where they get the minerals from. I have heard that these people actually go out rock hunting and find them themselves. I am not wondering where specifically they go and find each different type (I have no specific minerals I am interested in), just generally wondering if they are actually going out into the fields with a chisel and a brush and digging stuff up, putting them in their pockets, and then taking them home and cleaning them up.

If that's not the case, I wonder what they actually do to get them (at a high level).

If that is the case, then I am wondering how they actually (a) know where to look, and (b) are allowed to do that. To narrow this down, it sounds like there are a few scenarios:

There is just public land and you start looking without any mines or anything.
There is private land and you start looking without any mines or anything.
You go to a mine and somehow get permission to look around in the field.
Then my thoughts. Perhaps the "company" miners (or whoever is actually doing the main mine operation) is mining for rock A, and there are pockets of rock or mineral B scattered around, which would just go to waste. So the mineral collector asks to go through the "rock waste" and gets the minerals that way. That seems like the best way to get it in bulk.
You have direct access to the mine and the mine is for the specific mineral(s), so you are getting it in big chunks.

What I am wondering is this:

Who does 1-5. Wondering if most of the time (sort of thing) hobbyists do 1 and 2, and maybe if they are adventurous 3 or 4, while the "shops" do 5. The shops own the land and own the mine. Wondering generally (just a quick note) on what the behavior is like in looking for the rocks, if most of the time it's just browsing the field in broad areas, or no, you know exactly where you're going by checking with some expert nearby and are going to harvest a specific type of mineral.

I am also wondering how much work it takes to find stuff, and how to get permission to the mine, but those I might save for future questions, unless it's just a casual "just ask them and be nice" sort of thing :).

In the United States, mining minerals is similar to mining for precious metals (for the most part). You can establish a mining claim on a likely spot of Federal/State land and go to town. There are rules and regulations that guide the appropriate ways to establish, work and maintain a claim. You can also negotiate with a private land-owner for rights to mine on their land.

One step up is wholesale markets that sell mineral specimens (and all the items that go with them). There is a huge one in Tucson AZ in Jan/Feb with an amazing spectrum of stuff.

These markets are where most small retailers go to get their product.


Changes in Earth's orbital and rotation speeds What are the Earth's maximum and minimum orbital speeds around the Sun?

Is there any way to calculate orbital speed at any point of Earth's orbit? Is there a way to relate this to the calendar?

Does the change in speed during an orbit around the Sun affect Earth's revolution time around its own axis? (24 hours slightly more or less on day to day basis)

The Earth moves faster around the Sun when it is near its perihelion (the closest point of its orbit to the Sun). And it moves slower when it is further away (aphelion), just as Kepler realized quite a while ago when enunciating his Third Law of Planetary Motion. There are many ways to write a formula to calculate Earth's speed around the Sun. But for your question I think this one is simple and general enough:

$$v= \sqrt{G\,M_S\left(\frac{2}{r}-\frac{1}{a}\right)}$$

Where $v$ is Earth's speed, $G$ is the gravitational constant, $M_s$ is the mass of the Sun (this equation assumes that the mass of Earth is negligible compared to the mass of the Sun, which is a very good approximation), $a$ is Earth's semi-major axis of orbit (which defines how elliptic or how circular the orbit is), and $r$ is the distance from the Earth to the Sun.

And the closest and furthest distances respectively are about 147.1 million kilometers (around January 3) and about 152.1 million kilometers (around July 4). Plugging those numbers into the equation you get a maximum speed of 30.3 km/s and a minimum of 29.3 km/s. In contrast, the speed due to Earth's rotation around its own axis, is at most (i.e. in the equator) about 0.5 km/s.

For any given day, the calculation of the distance to the Sun is complicated, but websites like this one, provide a real time value you can use in the above formula [that site also provides the speed right away!].

These values are basically the same from one year to another. However, they do slowly change as the eccentricity of Earth's orbit gradually varies over a ~400,000 years cycle as described by the Milankovitch cycles.

Now, for Earth's speed of rotation about its own axis the value is pretty much the same each day; variations are of day length are on the order of a fraction of a millisecond.  Part of that variation is periodic and more or less predictable and another part is from other less predictable factors. But for all practical purposes the length of the day is constant through the year. The following figure shows those tiny variations in day length since the early 1960's:

(image from Wikipedia commons, originally here)

But as a consequence of these tiny variations, almost every year one or two (leap seconds) are added to our clocks to keep them aligned with the rotation of the Earth. In the long run (millennia), Earth days are getting longer (~0.017 milliseconds per year).  Some of the factors involved were discussed in this question.

Finally to address whether changes in orbital speed affect rotational speed: I don't think so. For what I understand none of those small changes in the length of the day is a direct consequence of changes in the orbital speed. However, despite there is no changes in the speed of rotation, what we generally understand as a day (i.e. the time between two consecutive sunrises, sunsets or noon), is not only controlled by the rotation of the Earth around its axis. In fact, one out of the ~365 days of the year is consequence of Earth's revolution around the Sun, not its rotation. And that one-day contribution give rise to the difference between a day and a sidereal day, and the variations in the duration of the apparent solar day, variations that are directly controlled by Earth's orbital speed and can change the time between solar noon up to about 30 seconds over a year.


Do hurricanes cool the earth? I noticed that temperature drops in the surrounding area of a hurricane.

Is the heat converted into kinetic energy?
Could the shape of the hurricanes reflect sunlight?
Do they create more lightning in an area that would normally have lower levels of lightning for the same timeframe, in turn creating more ozone?

Hurricanes can be viewed as having primary and secondary circulations. The primary circulation is what we see in satellite photos, comprising the winds and clouds that circle the low pressure zone at the center of the hurricane. The secondary circulation is a vast heat engine that provides the energy needed to sustain the primary circulation.

The low pressure cell at the center draws surface air toward the center, gathering moisture from the warm ocean along the way. This flow is more or less isothermal.
Humid air rises in the clouds around the center of the storm, releasing moisture along the way. This rise is more or less adiabatic.
The now dry air at the top of the troposphere flows outward and radiates energy into space. This flow is roughly isothermal.
Finally, the air falls in downdrafts at the outer edges of the storm. Like the updrafts near the eye wall, the flow in these downdrafts is more or less adiabatic. From here the cycle repeats.

This heat engine, powered by a hundred kelvin temperature difference between the warm oceans and the top of the troposphere, does a very nice job of locally cooling the Earth.


Why does relative humidity seem to correlate with high temperature (at least where I live)? I live in New Jersey.  Now that summer is coming on us, temperatures and outdoor relative humidity are both increasing.  I've noticed the few years that I've lived here that there seems to be a rough correlation with a day's high temperature and the relative humidity.  I've always found this odd, since for a fixed amount of moisture in the air, relative humidity will go down with increasing air temperature.  However, the hottest days (as the thermometer reads, not just as I feel) also seem to have the highest relative humidity.

I lived in Hong Kong for two years and the same thing seemed to happen there.  The hottest days also had the highest humidity (and were usually accompanied with the formation of a typhoon).

What makes relative humidity go up with hotter days?

In coastal New Jersey, relative humidity is maximal in the early fall when the ocean temperature is warmest, and minimal in early spring when the ocean is coldest.  However, the monthly variation is rather small:

Atlantic City, New Jersey:

70 January
69 February
67 March
66 April
71 May
73 June
74 July
76 August
76 September
75 October
73 November
71 December
72 Annual

Newark, New Jersey

65 January
63 February
60 March
58 April
62 May
63 June
63 July
66 August
68 September
66 October
67 November
67 December
64 Annual

source: https://www.currentresults.com/Weather/New-Jersey/humidity-by-month.php


Can the previous weather be computed from the current situation? If one applies today's state-of-the-art weather forecast computations "backwards", i.e. computing how the systems was X days before the current situation based on knowledge of today's situation, at which point do "predictions" deviate significantly from the (known) sitautions ?

In other words, are those computations reversible and even possible?
And if so, is the error level comparabliy (i.e. time-symmetric) or not?

Edit:
Imagine one would get the data from an Earth-like planet through an observation (satelite etc.) at a given moment, would current weather-models allow to compute how the weather was before that time?

The underlying equations for fluid-dynamic models are hyperbolic partial differential equations. They can generally be written in the form
$$
  \frac{\partial}{\partial t} u(t) = D(u(t))
$$
where $D$ in some way evaluates the current state of the system and its spatial derivatives.

A numerical simulation then integrates this differential equation, to extrapolate from a start state $u(t_0) = u_0$ the time-dependent $u(t)|_{t>t_0}$.

Well, if we can do that, then surely we could also solve in the inverse time direction, by considering the equation
$$
  \frac{\partial}{\partial t} u(-t) = -D(u(t))
$$
and running the integrator with $\tilde t = -t$, $\tilde D = -D$?

Actually, you quickly run into problems when you try that. The operator $D$ can be characterised by its Jacobian, which basically tells you how pertubations in the state influence the derivative. Specifically, the complex eigenvalues of the Jacobian can tell you whether a small deviation will a) amplify over time (positive real part), or b) decay (negative real part), or c) just oscillate (purely imaginary).

For physical systems the eigenvalues tend to be mostly c) or b): you get a lot of wave-like solutions which propagate / oscillate over the system, and tend to decay over time. a) however is more tricky: if you start with a small deviation from the start state, the system will over time deviate ever more and and more. Now, this kind of thing is by no means unheard of especially in meteorology; it's the essence of a chaotic system. Storms can emerge and grow stronger over time, but only by scooping up energy that's already stored in the system. At some point they'll stop.

OTOH, you always have a lot of consistently negative real-part eigenvalues. These correspond to dissipative effects: small-scale pertubations generally are smoothed out to zero by the physical effects, e.g. winds have friction, mixing of air of different temperature averages out the differences, etc.. If you now run the simulation backwards, you turn those negative real parts into positive real parts, and that means the system is suddenly massively chaotic on all length scales. Small pertubation arise out of numerical uncertainties, and grow over all bounds. You would not only end up with states different from the actual weather a week ago, but with states that are completely unlike anything the weather has ever been like – huge, erratic temperature fluctuations and small vortices with crazy wind speeds.


Method to determine Tmax 95th percentile in a climate data I am analyzing the effect of extreme weather on milk production (Panel data). I am looking at direct effects and indirect effects of weather on animal (milk production).

Regarding extreme weather, I am looking at the following variables - Tmin, Tmax and Precipitation. The dependent variable (milk litres) is a monthly cumulative value. Therefore, I have to generate more meaningful extreme weather variables at the monthly level. For e.g. No of days of Tmax > 95th percentile, No of days of Temperature Humidity Index (THI) at certain threshold, etc. To determine the no of days of Tmax >95th percentile, I have used the following method.

I have calculated the Tmax value of 95th percentile for each month and for each farm  using the base period data 1980-2010. Then I have applied the determined value on daywise data (2011-2015) to determine whether the day value is exceeding the 95th percentile value. If it exceeds, then given 1 else 0. Then aggregated the no of days (with Tmax >95th percentile) by month. Do you think that this method will identify the extremes?

Recently, I have come across a method to calculate daywise percentiles, high daily temperature for a specific day in a year with the high temperature for that same day across all years. Days with above 95th percentile are selected as events.

I have tried to compare both the methods for a farm location. I found that previous method (monthwise percentiles) identify less number of events in comparison to the recent method.

Suggestions are welcome to use the correct method.

You're heading along the right lines, but there are a few things you might want to make sure you've thought about when deciding on your method.

1. Notation

A long time ago there was an Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI) that came up with some naming conventions for various climate indices, because it gets a bit cumbersome to talk about things like "the annual minimum of daily maxima" all the time.  They were first described in this paper:

Alexander et al. (2006), Global observed changes in daily climate extremes of temperature and precipitation, J. Geophys. Res., 111, D05109, doi:10.1029/2005JD006290

In your case, the 95th percentile of daily maximum temperature (TX) would be called TX95p.

2. Think about your science question

Most temperature time series for the last few decades will contain a warming trend, which has the effect that hot days will occur more frequently in the later part of the data than the earlier part.  You need to think about what aspect of temperature causes the impact in the system you're studying to decide if you need to detrend the data or not.  If the problem occurs when the absolute temperature exceeds some limit, then you probably don't want to detrend.  If the the system can adapt to the mean change but the problem occurs if the hot days occur in clusters, then you may want to detrend the data.

You need to make similar decisions about de-seasonalising the data, which you're currently doing by considering each calendar month separately when estimating TX95p.  In most cases it does make sense to de-seasonalise the data, particularly in places with a large annual cycle.  While you're at it, think about whether you need to analyse the whole year.  If the impact you're worried about only occurs in a particular season, then target your analysis to that season: e.g., a warm extreme in summer typically has a greater impact than a warm extreme in winter.

3. Estimating TX95p

Unless you have some specific hypothesis or protocol that needs to separate the periods, I'd use all years of data (1980-2015) to estimate TX95p.  If you're assuming that TX95p is stationary between the periods, then using more years will give you a more accurate estimate of the threshold.

  Recently, I have come across a method to calculate daywise percentiles, high daily temperature for a specific day in a year with the high temperature for that same day across all years. Days with above 95th percentile are selected as events.

What you've found here it that there's no standard way of estimating TX95p, the climatological threshold for a hot day.  A quick glance through my notes throws up various methods:

Daily climatology using 15-day window centred on day-of-year (Della-Marta et al, 2007; Fischer and Schaer, 2010; Perkins et al, 2012; Teng et al, 2013)
Daily climatology using 10-day window centred on day-of-year after detrending the data (Kreuger et al, 2015)
Daily climatology using 5-day window centred on day-of-year (Lorenz et al, 2010; Mueller and Seneviratne, 2012)
Daily climatology using 1-day window and then smoothed with a Fast Fourier Transform (Eade et al, 2012).
Single threshold value using all daily TX in summers (Vautard et al, 2013).

  I have tried to compare both the methods for a farm location. I found that previous method (monthwise percentiles) identify less number of events in comparison to the recent method.

I suspect that trying to estimate daily TX95p from just 31 values for each day of year gives very inaccurate results, whereas estimating monthly TX95p from about 930 (31*30) values is more realistic.  The daily estimates probably jump around from one day of year to the next, which would clearly be a sampling artefact, and yield values that are quite close to TX100p, so you diagnose fewer hot days.  This is why the papers listed above use various smoothing methods.


Thickening Mars's Atmosphere if we were to send a mission to mars (unlimited budget WE WISH!) to explore different methods that would enable us to thicken the martian atmosphere, what different types of data should this mission capture and how could this help is in exploring potential methods to thicken the martian atmosphere.

We are already knowledgeable about some aspects of the requirements needed to terraform Mars & the Moon. As @David_Garcia_Bodego mentions in his comments, gravity is a major factor in celestial bodies being able to retain an atmosphere.

This is because the gravity of a celestial body affects the escape velocity  of that body. The other important factor is the surface temperature of the celestial body. This is why Titan, a satellite of Saturn, has a thick atmosphere, despite having a similar escape velocity to the Moon (Luna), it is much colder and has a thick atmosphere.

Another factor that assists Titan in maintaining a thick atmosphere is its distance from the Sun and the weaker effect of the solar wind at that distance. Also, Titan is protected by Saturn's magnetosphere.

I recommend reading:

What will happen to the air released from the Moon's Surface?
Could the Moon keep an atmosphere?

and the links contained within those questions.

Yes, these questions discuss the Moon and not Mars, but the information provided in those questions is applicable to Mars.

The graph below provides a visual of the gases a celestial body can retain in a atmosphere based on escape velocity and temperature.

Factors that act in favor of Mars being able to have a thick atmosphere are:

Mars is farther away from the Sun than Earth & Luna so it experiences
a weaker solar wind.
The surface temperature of Mars is cold, which reduces the energy of
atmospheric molecules.

Factors that act against Mars being able to have a thick atmosphere are:

The gravity of Mars and subsequently the escape velocity of Mars is small.
The lack of a magnetosphere to shield the atmosphere from solar wind.


How exactly is the "global average temperature" calculated and how reasonable is this method? During the recent (2015) Paris climate negotiations there was a lot of talk in the media about "limiting the global temperature increase to 2 degrees Celsius".
I keep wondering about what this value of 2 degrees really means, and what can we read from this value.  It is said to refer to some sort of global average temperature. How is this average calculated, how meaningful can it be?
Temperature is what physicists call an intensive quantity, as opposed to extensive quantities which are additive.  Thus there is no physically natural way to define an "average temperature".  Any averaging process will necessarily be arbitrary and ad hoc.  It can be done through space and through time, with various sampling frequencies in both, and with various averaging methods (arithmetic, geometric, various weighted versions, etc.).  It is indeed possible to construct pathological functions $f(x)$ the estimated average of which will be wildly different based on the averaging method, or even based on something as innocent looking as the sampling frequency.
Of course these difficulties don't mean that any average of an intensive quantity is meaningless.  It is completely reasonable to try to mathematically formalize the intuitive concept of warming.  But they do mean that it has to be done carefully.  It is also quite striking for those of us who are not climate scientist that the amount of warming we are talking about is on a scale (0-2 $^\circ$C) that is much smaller than the temperature variation we might experience during a time scale as short as a day or distance scales as short as a few hundred of kilometers.
So, to finally come to concrete questions:

How is this average calculated exactly?  Why is the specific method used considered to be reasonable?

It is also quite striking for those of us who are not climate
scientist that the amount of warming we are talking about is on a
scale (0-2 C) that is much smaller than the temperature variation we
might experience during a time scale as short as a day or distance
scales as short as a few hundred of kilometers.

TLDR, but here goes:
There's a few factors to consider regarding the relatively tiny 2 degrees C and I'm not sure how to explain this without being long, but obviously you're correct, we hardly notice a 2 degree change ourselves.   But if you look at the total energy of Earth you can get a slightly better picture.
The numbers below are only approximations but should be close enough to give an idea of how the trapped heat plays in the Earth's atmosphere and oceans.
The sun shines on the Earth about 1.8x1017 Joules per second, or about 5.6x1024 Joules per year.   Source.   Remember that number, I'll reference it a few times.
The rough division is about 48% of that hits the surface, 23% is absorbed in the atmosphere, 29% is reflected back into space.  Source.  Now, because the Earth is in largely in a stable equilibrium where energy in roughly equals energy out, the Earth radiates about the equivalent of 71% of that 5.6x1024 Joules per year that the sun shines on it, the other 29% being reflected.
This will be obvious to some but I'll mention it anyway.   Global warming has nothing to do with the sun giving the Earth more energy.   It has to do with the Earth radiating less energy into space, at least until the Earth warms enough for a new equilibrium to re-stabilize the energy in = energy out.   Raising the concentration of greenhouse gas changes the equilibrium of heat transfer.   It's the same principal as putting on a sweater.
Using the same link as above, 59 of that 71% radiates from Earth's upper atmosphere and the remaining 12% from the surface.  For greenhouse gas driven climate change to work, the only way that can work is that the 59% needs to drop (OK, not the only way, you can also play with albedo).  But heat is trapped in the lower atmosphere, the upper atmosphere cools and the 59% drops a little lower.   Cloud cover and changes in Albedo such as snow cover, ocean cover and green vs desert are factors too, (the 29% mentioned above), but that gets enormously complicated, and beyond the scope of anything I can try to explain, so I'm going to ignore that for now and just look at the 59% of the 5.6x1024 Joules per year.
Thermal radiation increases at roughly the 4th power of the temperature, so if we use the average temperature on Earth at about 288 Kelvin and add 2 degrees to that, the radiation difference between 288 Kelvin and 290 Kelvin using the 4th power rule is a 2.8% increase, or an increase from 12% to 12.34% of the 5.6x1024.   To keep the energy balance consistent, when a new equilibrium is reached, the 59% drops to 58.66% with 0.34% being "new heat" due to the additional greenhouse gas.   This change presumably has already happened.  In fact, today, the heat balance is out of equilibrium which is why the Earth is warming.   The Earth is taking in more heat than it's giving back into space.
0.34% of 5.6x1024 = 1.9x1022 Joules.  By comparison, the combined energy use of all man-kind is about 1/40th of that, or about 5x1020th Joules.  Source.   So, from a human perspective it's an enormous amount of energy but to the something the size of the Earth it's quite small.   Needless to say, the 0.34% estimate is pretty rough, so take the numbers below with some flexibility, but they're also, at least somewhat in the range.
Second, we have to consider where the heat is going.   By most estimates, more than 90% of this goes into the oceans and about 90% or a bit more of the heat is going into the oceans with some melting ice, some going into the ground and melting tundra and only a small percentage going into the atmosphere where surface temperatures are calculated.
Source, Source and Source (The first mentions a very specific 93.4% into the oceans and 2.3 into the Atmosphere.   The last 2 mention "more than 90%" and "about 90%", so there might be some uncertainty on the precise ratio and I'm going to round up to 3%.   Feel free to re-run the numbers with 2.3%, 4%, whatever you like.
3% of 1.9x1022 = 5.8x1020  (not a typo, it's actually 1.93)
So the atmosphere, by rough estimates, adds about 5.8x1020 Joules of energy as a result of the increase in CO2.  So, to estimate the expected warming from that amount of energy:
The mass of the Atmosphere is about 5.1x1021 grams.  Source.
About 4.2 joules can heat 1 gram of water 1 degree C.  Source, and the specific heat of the atmosphere is about 1/4.1 that of water, Source.   Of ocean water, slightly lower, I'm going to estimate 1/4.0
so, doing the maths: (4.0/4.2)x(5.1x1021/5.8x1020), my roughest of calculations says that we'd need about 9 years of trapped heat to warm the atmosphere 1 degree C.   If we use skeptical sciences 2.3% number, that ups it to about 11.5 years, and both estimates are obviously too aggressive.  The observed surface temperature warming is closer to 1 degree every 40-50 years, give or take, though the warming on land is faster than the warming over water.   But my estimate can't help but be quite rough.  It excludes albedo and cloud formation entirely, which is important, but trying to calculate is hugely complex and far above my pay-grade.   It's difficult to calculate the effects of clouds on global warming even with super-computers.
Now, obviously ocean currents, dictate varying amounts of heat exchanged between the ocean and the atmosphere, so one year to the next can vary by significantly more than 1/9th of 1 degree, but that's movement of heat, not new heat added to the system.
Now if I calculate how long it would take to heat the oceans, and as I understand it, the deep oceans aren't warming, but the surface and sometimes called "mid-oceans" or mid-depth are warming, (articles here and here
Using the numbers above, for 1 mile deep using with the estimate of about 33 times the heat going into the oceans than into the atmosphere, reapplying the specific heat of water to atmosphere ratio of 4 to 1 and estimating the mass of 1 mile of ocean water equivalent to about 160 atmospheres, adjusting for 71% of surface cover, it comes to a rough estimate of 124 years for my very rough heat trapping estimate to warm 1 mile of oceans about 1 degree C.   I couldn't find any precise warming in the oceans, but 1 degree of warming, 1 mile deep in 124 years sounds roughly in the neighborhood of what the experts expect. (I think).
So, long story short, while local temperature can change significantly over different parts of the day, global average temperature isn't nearly so easily changed.  On a single day (using numbers above), the Earth gets 71% of 5.6x1024/365 or about 1.1x1022 joules, and an amount quite close to that radiates away from the earth every day too.   Based on my very rough estimate, the difference between heat the Earth takes in and heat the Earth radiates is about 0.3%.  On individual days you might get a fair bit bigger than a 0.3% difference, but there's still not enough heat added by 1 day of sunlight to significantly change the Earth's global average temperature.
Now, obviously, the Earth's surface warms measurably under daylight but that's because 48% of the suns energy reaches the surface directly and the heat is localized, and while 1/2 of the Earth's surface warms the other half cools, so it tends to average out.    There's insufficient energy in sunlight to make much change to global average temperature over a short period of time.
With that in mind, the 2 degrees that the IPCC discusses, which includes ocean heat trapping, is quite significant.    It more likely works out to about 3 degrees on land, 1.5 degrees over water, with rising oceans due to both thermal expansion and melting ice.   Warmer oceans means bigger hurricanes.   It's easy to say "2 degrees won't matter", but the models say it actually might.   It's a pretty significant variation.  It also takes quite a bit of time for the 40% increase in CO2 to create that much warming, which is why the projections of 2 degrees warming go out to about 2100.
Another way to point out lack of global temperature variation is to look at the charts for global average temperature.   while, I couldn't find any charts for daily variation of average global temperatures, I found some monthly variation charts here.  Source.   Assuming the monthly averages have gotten more accurate in recent decades, The average global temperature change month to month is about 0.13 degrees C over land and about 0.095 degrees C over oceans since 1980, with the largest month to month variation about 0.47 degrees C over land 0.36 over oceans.  There's probably some rounding errors in there, but there's clearly a degree of consistency to global average surface temperature and even more consistency to surface temperature over the oceans, and that's exactly what we should expect, having looked at the heat in and heat out.
Local affects are driven by circulation, but circulation is simply the moving of heat from one place to another.  Circulation isn't the creation of heat but the behavior of heat and differences in air pressures and it doesn't measurably add any heat to the system.
Corrections to my too long answer welcome.


Red volcanic soils - what are the likely constituents? I live very near an extinct Andesite volcano and hiking in that area I've noticed bands of soil that have a dark red coloration. I've also been in Kauai, one of the volcanic islands of Hawaii, but those soils appear to be a lighter, almost orange color which I've heard is attributed to iron content.

So for the soil in my local neighborhood, what is the likely constituent that gives it the dark red color? Is there a simple chemical test I can use to confirm it's iron?

tl;dr

If it's red, it's iron.
If it's soil, it probably has iron even if it's not red.
Therefore there's no point testing it for iron (in a simple way), because you can be confident it's there.

I'd like to add a bit to Jezibelle's answer. First of all, you could do a simple chemical test to test for iron, but that would not give you much. Iron oxides on the surface are extremely insoluble in water. You would either have to use LOTS of soil and water to test it, or use acids that will dissolve it and then it's not a simple test anymore.

Another reason is that assuming you do that test, it is going to be positive for iron. Andesite has iron in it. This and just about every other rock you can find have iron in it. Those that don't, are not red. The colour that you're seeing is enough proof that there's iron in it.

Now the question is which iron oxide is it. Pure hematite ($\ce{Fe2O3}$) is deep dark red. Pure goethite ($\ce{FeO(OH).H2O}$) is yellow. But then you have everything in between, and mixtures (given the general name: limonite). Now remember, iron is not the only constituent of soil. Silicon is the most abundant metal in soils, followed by aluminum, sodium, calcium, magnesium and potassium (not necessarily in that order). These elements can combine with iron to form stuff that doesn't even have to be red. It can be grey, black, green and everything in between.


What is that spooky humming sound heard in earthquake footages? In most of the earthquake footages filmed outside during the earthquake that hit Mexico City on September 9, 2017 there was a distinctive streak of hum in rapid succession that could be heard in the background. It sounded like someone is constantly hitting the tuning forks onto a light tower like 2 times per second.

You can find numerous footages on youtube, but I picked one and fetched the audio portion covering the hums, you can listen to the audio at this link here (sorry I did not know how to upload an audio to SE).

Here is the waveform of the sound

What is that sound? What is causing this sound? If this was buildings or surrounding objects, why is there a pattern? Why is this sound heard in every footage no matter where they are filmed as long as they were filmed outside.

Wailing sirens.

Examples 1, 2 where you see people come running out, i.e. exactly when you'd expect sirens, or 3, or 4 and 5 where they are explicitly mentioned.


Do our continents lay on the mantle because solid silicon dioxide is less dense than its liquid form? I don't know whether quartz behaves like ice or not, but could it be because silicon dioxide, which the continents are made of for a big part, is less dense - so the continents lay on top like ice on water?

Even if the mantle was pure silica, it wouldn't melt at great depth because of the pressure and paucity of volatiles at that depth (which would act like fluxes, depressing the melting point). So it wouldn't behave like a solid phase floating on a chemically similar liquid phase.

For the most part the crust is not silica but a mix of silica and alumino-silicates of calcium, sodium and potassium, with traces of a whole lot of other stuff. The average specific gravity is about 2.8. On the other hand the mantle is predominantly a mixture of magnesium-iron silicates, with a little calcium, nickel, chromium, etc, and an average specific gravity of about 3.2.  So it is a case of silica-rich (not pure silica) rocks floating on much denser silicates, depleted in aluminium, and relatively depleted on silica. The biggest difference is the high iron content of the mantle.

I suspect confusion arises because many people are not clear about the distinction between quartz silica, which always has a specific gravity of 2.65, and silicates, where the density is highly variable between about 2.0 and 4.7.


Determing whether an area is Inland or Coastal I have determined an area to be along the coastline just from looking at its climagraph. Its temperatures only range from -10 to 21 so there is not a large range of temperatures because it is being moderated by the ocean. However now I need to see if the wind speeds provided back my answer up. The windspeeds range from 10.7 km/hr to 15km/hr and there is only 8 days a year where the windspeeds are greater or equal to 52km/hr. So I was not given the name of this location but just from this information about windspeeds I need to back up my answer saying that this region is a coastline region. But how do I go about that?

Well, let's start with a rough global map (from NCEP Reanalysis) of the average winds speeds (in meters per second):

Multiply by 3.6 to get km/hr.  So your range is basically from 3 m/s to 4 m/s.  So you're looking at the medium blue color basically.
There are some coastal locations.  But generally, coastal locations will have quite a bit of wind...

What this graphic says is that basically winds at the ocean are 15-60% increased from typical land values.  Even more upsetting to being coastal is the 8 days less than 52 km/hr that you mention.  You're in a location reasonably mid-latitude, so you've traditionally got the big wind storms that often affect the coastal areas, such as Nor'Easters, and Bering Sea cyclones.  I'd think it'd be hard to find an oceanic city that doesn't get above 52 km/hr more than 8 days during a year outside the tropics (assuming you're talking about short burst of 52 km/hr and not daily averages, but even daily averages I'd think might surpass 52 km/hr 8 days per year in the majority of seaboard cities).

So I'd be surprised to see that it is truly a coastal location.  However there are a couple places with connections to water that might fit still.
 1 - Near inland seas\lakes would have somewhat lower wind because of the diminished water fetch available and the decreased percentage of the year that wind flows over such water.
 2 - The transition zone from marine winds to land winds is probably only something like 10-100 miles, while temperature moderation is still significant, even moreso if there is water on many sides.

Because your temperature range is only indeed 31 C (56 F) wide, that certainly does seem to still suggest it has significant moisture influences.

Now, 21 C seems a fairly cool value (especially if that's the absolute maximum daytime peak during the year, but even an average of 21 seems a tad cool, especially for cities not right on the water.
So that suggests to me that it's pretty far north, or perhaps abuts rather cool waters.

So, looking at the map, and based upon those ideas, I'd think the favorite might be inland Russia or China... or maybe around Italy\Greece.  Just the right city location in the northern US or Canada might work too, like Portland (Oregon), Detroit, or Ottawa.


How could this "aztec temple" mountain (or volcano) have been formed on Antarctica? [Update: This was not a duplicate of the other question since the mountain shape is rather different. This was already stated in my question below.]

This question is a bit similar to this other question about pyramid-shaped mountains.

In this case though the mountain is also in Antarctica but it looks as shown in below picture.

(This picture is taken at Princess Elisabeth station)

So I was curious on if this mountain in the foreground, and the one behind it, could be volcanoes? Or are there examples where non-volcano mountains form into these shapes?

Remember that Antarctica is covered in a sheet of ice. Strip away the ice and you get something like this:

(Source:Wikimedia Commons)

This is the Matterhorn in the Alps on the Swiss-Italian border. The word horn is used in glacial geomorphology to refer to a mountain peak that has been ground by glaciers on many sides to create a "pyramidal peak" with sheer, faceted sides.

During the Pleistocene ice ages, the Alps were covered in an ice sheet much like Antarctica is today, and undoubtedly at some point the tip of the Matterhorn poked through the top of the ice, looking very similar to the mountain in your picture.


Is it possible that we can reduce climate change given our current actions? Today, there are some scientists and people that are working on projects that will reduce the production of CO2 levels and effects of climate change. I'm very confused on whether it is possible for there to be enough change such that climate change can reduce and soon come to a stable level?

Our current actions are most definitely not enough to reduce the rate of climate change.  Yes, it is possible that someday we could do enough to start reversing the damage, but we aren't anywhere close to that reality given our social customs that constantly rely on combustion.  Definitely not anything "soon".

The reality is that emissions still go up nearly every year.  This is largely because most of the world (especially China) is actively converting to "western" lifestyle, which uses a lot of resources per capita.  Also, it takes hundreds of years for CO2 to decrease in the atmosphere naturally.  So, while there are many efforts to reduce CO2 emissions, the amount of carbon in the atmosphere still goes up every year.  If we could somehow advance carbon sequestration methods to  the point where we can reduce both oceanic and atmospheric carbon, then we could theoretically get back to "normal".  To truly make a change in the right direction, though, the industrialized world needs to stop relying on combustion as the dominant energy source.  See the http://www.globalcarbonproject.org/carbonbudget/index.htm slides (excerpt below) for more information.

Emissions from fossil fuel use and industry:

And here is the atmospheric concentration as measured at Mauna Loa:


What causes the entrainment of atmospheric gases towards a volcanic ash/tephra plume? I understand that volcanic ash plumes can only rise to great heights (e.g. 50km) with the help of some other processes, as the velocity of the material ejected isn't great enough to send it high into the atmosphere.

I don't understand how exactly these processes take place. I think that cooler, atmospheric gases are entrained towards the hotter, denser volcanic plume, then become heated and incorporated into the ash plume, causing it to become buoyant and to expand.

What causes the cool, atmospheric gas to move towards the plume? Is it due to the temperature differences between the plume and the atmosphere, or some kind of pressure difference?

This answer seeks to just answer about ambient air entrainment, as per the question (not eruptive plume height, as suggested in the comments) which is a separate question.

According to the book, Modeling Volcanic Processes: The Physics and Mathematics of Volcanism, (Fagents et al, 2012, p. 155-156), your assumption (2nd paragraph) is on the right track, particularly for energetic eruptions (e.g. Plinian).

When the plume initially erupts, it possesses significant momentum, with a greater density and are influenced by pressures considerably greater than the ambient atmosphere.  However, once in the atmosphere, the plume undergoes rapid decompression and expands, ascending as a turbulent flow in the convective ascent region (an example is shown below).

Image source: USGS page about the Mt St Helens eruption in 1980 demonstrating the turbulence in an eruptive column.

As the flow continues to ascend, the eruptive column begins to exhibit lateral gradients in temperature, momentum and density, allowing for the mixing with the ambient air at the edges of the column - over time, this mixing continues to the core of the eruptive column by shear mixing.  Effectively, 'stirred into the column by the turbulence'.(Fagents et al. 2012; Kaminski et al. 2011).

Image source: MTU.edu

As the entrained air heats, expands and rises, more cooler ambient air is mixed into the turbulent eruptive column (just as long as the eruption continues) - as per the MTU.edu diagram above, the plume rises by buoyant convection.

Entrainment of air into the eruptive column can be increased by the right wind conditions, as observed at the 2011 Kirishima-Shinmoe-dake volcano eruption in Japan (Kozono et al. 2014).

Additional resources

Kozono et al. 2014, Correlation between magma chamber deflation and eruption cloud height during the 2011 Shinmoe-dake eruptions, Earth, Planets and Space

Kaminski et al. 2011, Rise of volcanic plumes to the stratosphere aided by penetrative convection above
large lava flows, Earth and Planetary Science Letters


How big of an event is needed to trigger a long winter? Could a small meteor or natural nuclear explosion melt an ice cap on Earth to trigger a mini ice age without the event being observed by people?

Can the Earth have an overlaying thermal cycle that collects heat until it triggers long global winter?

A small meteor/asteroid impact might trigger a nuclear winter, but it would be registered by people and it would be very unlikely to trigger an ice age unless the impact created a very large amount of dust in the atmosphere. The dust would need to stay in the atmosphere for a decade or more to trigger an ice age.

A natural nuclear explosion cannot be very large because as soon as critical mass is reached it will explode so the size of the explosion is in a way self limiting. If this happened under the world's major ice sheets it will melt a relatively large amount of ice but this would be registered by an increase in radioactivity in sea water (possibly many years after the explosion took place). So this would not trigger an ice age.

A large volcanic eruption can cool the earth for a few years but is unlikely to trigger an ice age unless it lasts for several decades, and yest again, this would be registered by people. You can take a look here to see what kind of magnitudes that have happened in our history https://www.ranker.com/list/the-worst-volcanic-eruptions-in-history/drake-bird

When you ask about an overlaying thermal cycle (as in heating until the temperature crashes), this is very unlikely to happen unless the temperature reaches a point where a very large part of life gets eradicated, as the temperature on earth goes up the ocean can hold less and less CO2 until at one point the oceans starts to release more CO2 than it absorbs from the atmosphere. This means the heating will not trigger cooling unless life on our planet is significantly reduced.

Water can hold less dissolved gasses when the temperature goes up, so at one point aerobic life in the ocean can no longer survive due to the lack of dissolved oxygen in the water.

This is just about how serious it might get if we keep on going like we are now.


What is the age of the earth's oil? Oil in the ground is found under the oceans and seas. It is made of dead fish. But from what period are those fish? I heard they are about 119 million years old. But fish exist much longer than that. So is it clear how old our oil is?

Oil can be generated from pretty much anything organic. The oldest oil that I know of comes from a porous Eocambrian siltstone in the Sultanate of Oman. This was formed nearly 200 million years before there were any fish around.
Apart from that, oil can be formed in any of the geological eras up to the late Cenozoic.


The halocline and sonar  I studied oceanography many years ago at university and recall a lecturer claiming that submarines in the second world war could pass undetected through the entrance to the Mediterranean.  He claimed that the halocline caused by the different salinities of the Atlantic and Mediterranean seas would be enough to deflect sonar thus making the submarine invisible. Has anyone seen evidence to support this?

Because of the limitations of wartime sonar, U-boats could sometimes pass undetected into the Mediterranean through the Straits of Gibraltar, but it was always risky and avoiding detection couldn't be guaranteed.

There were many things that limited the efficiency of sonar (or ASDIC as the British called it). It is true that sea water has a tendency to separate itself into layers which sonar finds difficult to penetrate. Sometimes this layering was based on differences in salinity, sometimes on differences in temperature, and sometimes on intervening sea currents. Even ships wakes could deflect the sonar beam, so sometimes powerful curving wakes were deliberately made by the U-boat to shake off a pursuing warship.

The range of active sonar under good conditions was normally a few miles, but that could be reduced if there was a lot of background noise. The Gibraltar straits are about 12 miles wide.  Whales and schools of fish could also send back false echoes which would fool all but the most experienced sonar operators.


Is Alert (in Canada) a harbor/port? Alert, in Qikiqtaaluk Region, Nunavut, Canada, is northernmost permanently inhabited place in world.
The site was first visited by Sir George Nares, who commanded HMS Alert in 1875-76, the first vessel to land on the shores of northern Ellesmere Island.
Is Alert a harbor/port? (I've read a few papers about Alert, but I haven't found the answer.)

Wikipedia does not include Alert as a port.  As the comments suggest, there is too much sea ice at that latitude to merit the infrastructure required of a port.  The northernmost port in the world is identified here as Dikson, Russia, at 73°30' N.
Supplies to Alert are delivered by air; the settlement does include an air port.