What is the most optimal latitude on Earth for the generation of extreme maximum temperatures? First question on this StackExchange, so here goes...

Overall, reaching high temperatures is dependent on 2 factors:

The (maximum) solar angle in the day. The greater the solar angle, the more insolation is received by the surface and air, allowing higher maximum temperatures assuming no thermal inertia.
The length of the day. The longer the day, the more total solar radiation arrives in one 24-hour span, and the shorter the night is to radiate off excess energy, both of which due to the thermal inertia of the atmosphere and ground bias them towards hot temperatures.

(Again due to thermal inertia, it may be dependent on the day length and solar angle of previous days, though this influence is more minor.)

The first factor explains why even though at the summer solstice the poles accumulate more solar energy over 24 hours than any other place on Earth (I know I had a source on this. I can't find it, though.), they are still extremely cold as the low solar angle prevents reaching higher temperatures. The second factor explains why even though the equatorial region has the highest average maximum solar angles throughout the year, they don't get especially hot (even in rare desert areas) as the day length is nearly constant throughout the year.

Ergo, the outer tropics and the subtropics experience the hottest extreme maximum temperatures on Earth. This can be seen in the records for each continent that has a large stretch in that area:

America (South): 48.9 °C in Rivadavia, Argentina (24.18[3]° S)
Africa (South): 50 °C in Dunbrody, South Africa (~33.4° S)
Australia: 50.7 °C in Oodnadatta, South Australia (27.54811° S)
Africa (North): 51.3/53.5 °C in Ouargla, Algeria (31.95° N)
Asia: 53.9 °C in Mitribah, Kuwait (29.81[6]° N)
and lastly, America (North): 54.0/54.4/56.7 °C in Furnace Creek, California, USA at a rather high 36.458056° N.

Presumably, the spread in latitudes is due to the geography in those areas being much more suited to the generation of extreme heat than places at the "absolute ideal latitude". But what is this absolute ideal latitude? At what point from the equator do the combination of day length and solar angle in summer create the most optimal conditions for extreme heat, other factors being equal?

(My scientific wild ass guess is 30°, but I'd like a more educated answer.)

The places that get the hottest temperatures are close to the equator but not necessarily on the equator. They will be low lying places, perhaps below sea level, and 'enjoying' a continental climate. For the record books, they will also need to be places where a climatologist passes through at the right time to measure it. I see you mention some record temperatures in your question, but I don't remember off hand what the absolute world record temperature is. It won't be far short of 55 C, but what amazes me is how the people who measured such temperatures survived to tell the tale. The atmosphere must have been very dry. From the point of view of human wellbeing, in high humidity temperatures well short of world record don't feel well short, and are almost as dangerous.


How and why did the oceans form on Earth but not on other planets? Earth is the only planet in our solar system that has copious amounts of water on it.  Where did this water come from and why is there so much water on Earth compared to every other planet in the solar system?

Your assumption that there is not a lot of water elsewhere in the solar system is incorrect.  According the this article on NASA's website;

Missions in recent years have overturned our view of a dry solar system, returning mounting evidence of ample water from a vast array of locations.
Comets from the remote corners of our solar system are made of water and other ices. Orbiters, landers, and rovers reveal Mars as a watery world in the distant past -- a world that today may contain entire underground oceans of frozen water.

It also points out that

Jupiter's moon Europa has a frozen crust of water, covering a thick global ocean. By current estimates, it has twice as much water as all of Earth's oceans and rivers!

The perception that the rest of the solar system does not have a lot of water is probably due to the fact that the Earth is in the 'Goldilocks zone' where water can exist in all three phases at the surface of the planet.  The temperatures on the rest of the planets in the solar system are either so hot that it can only exist in a vapor phase or so cold that it can only exist in ice at the surface or liquid beneath.

Water actually was never present on Earth before its creation and that is for sure.

Astronomers realized that there are two ready-made sources: comets and asteroids, the solar system’s gravel strewn among planetary boulders. The primary difference between the two is that comets typically have a greater concentration of ingredients that vaporize when heated, accounting for their iconic gaseous tails. Both comets and asteroids can contain ice. And if, by colliding with Earth, they added the amount of material some scientists suspect, such bodies could easily have delivered oceans’ worth of water. Accordingly, each has been fingered as a suspect in the mystery.

Adjudicating between the two is a challenge, and over the years scientific judgment has swung from one to the other. Nevertheless, recent observations of their chemical makeups are tipping the scale toward asteroids. Researchers reported last year, for example, that the ratios of different forms of hydrogen in asteroids appear to better match what we find here on Earth. But the analyses are based on limited samples, meaning there’s a good chance we’ve not yet heard the final word


Why is Belgium (and Luxembourg, Switzerland, Austria, Norway) still above consumption CO2 levels per capita of 1990? While many others did go down "Consumption-based emissions reflect the consumption and lifestyle
choices of a country’s citizens."

Via this article https://ourworldindata.org/consumption-based-co2 I see that Belgium's consumption-based CO2 emissions per capita in 2018 is still above the level of 1990.

I wonder why?
Why are Belgium, Luxembourg, Switzerland, Austria, Norway still above their CO2 consumption levels, while many other neighbouring countries such as the Netherlands, France, Germany, Italy, Denmark, Poland, Sweden, Ireland, ... did manage to get their levels down?
Further more, I am wondering how they can correctly estimate the CO2 of all consumption? I believe this is not known for all brands/products?
P.S.: In 'Sources' we can read:

Consumption-based emissions are national or regional emissions which
have been adjusted for trade (i.e. territorial/production emissions
minus emissions embedded in exports, plus emissions embedded in
imports). If a country's consumption-based emissions are higher than
its production emissions it is a net importer of carbon dioxide.
The underlying source is an updated version of the paper by "Peters et
al. (2011). Growth in emission transfers via international trade from
1990 to 2008."
► (Updated to 2014) Peters, GP, Minx, JC, Weber, CL and Edenhofer, O 2011. Growth in emission transfers via international trade from 1990 to 2008. Proceedings of the National Academy of Sciences 108, 8903-8908: https://bg.copernicus.org/articles/9/3247/2012/bg-9-3247-2012.html
This updated data is available in the latest version of
the Global Carbon Budget.
► https://www.icos-cp.eu/science-and-impact/global-carbon-budget/2019 via https://www.icos-cp.eu/science-and-impact/global-carbon-budget
Our World in Data has calculated several additional metrics based on
the following metrics:
► Energy consumption data from BP Statistical Review of World Energy: https://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-energy.html
► Long-term GDP data from Maddison Project Database: https://www.rug.nl/ggdc/historicaldevelopment/maddison/releases/maddison-project-database-2018
► Population data from the UN World Population Prospects and
Gapminder: https://www.gapminder.org/ https://population.un.org/wpp/

My answer will not be complete, but consider one factor: population.
Belgium population per year:
1990    9,967,000
2000    10,251,000 (+10.2%)
2009    10,796,000 (+5.3%)
2018    11,376,070 (+5.4%)
On top of that, you are considering countries with relatively small population increasing significantly (Belgium, Austria, the Netherlands). Most of the population increase is from immigration and high fertility rate of the new population (see the CO2eq impact of about 9tons per capita on the parents due to a new born), with industrial powerhouses like Germany and Italy where a lot of the production has been delocalized in the same time period (check CO2 of Romania or Spain)

Because Europe's infinite wisdom. Jokes aside,
Their anti co2 nonsense has revoked utilization of cheap and clean natural gas.
Instead Europe to satiate it's energy demands now burns wood and trash.
Before coal became widely available, wood was used not just for heating homes but also for industrial processes; it was the prdominant energy source for humanity. Even if half the land surface of Britain had been covered with woodland we could have made 1.25 million tonnes of bar iron a year (a fraction of current consumption) and nothing else. Even with a much lower population than today's, manufactured goods in the land-based economy were the preserve of the elite. Deep green energy production – decentralised, based on the products of the land – is far more damaging to humanity than nuclear meltdown. If Europe shuts down their nuclear plants it will not be water, wind or sun, but fossil fuel and imported wood chips to run their industrial society.
Nuclear's biggest advantage besides the fact it doesn't atmospherically pollute. A kilowatt-hour worth of coal fired electricity produces about 2.07 lbs of CO2 or over a million tons per terawatt-hour. The nuclear plant in my home state produces 14.9 Terawatt-hours per year; preventing over 15 million tons of CO2 per year or over half a billion tons over the last 40 years. The US nuclear industry keeps 830 million tons of CO2 out of the air annually. The other thing is the power density and 24/7 reliability a Nuclear reactor takes up a few acres of land and on it's size produces about 10-20 terawatt-hours per year; a wind farm or solar farm covers hundreds of thousands of acres. Were 7 billion people; were gonna be 9 billion by 2050 and they're moving to cities from the villages, the world is now 50% urban, up from 14% in 1900, it's gonna be 60% urban people by 2030, and 80% urban by 2050 that's 7 BILLION people living in cities and with it a appetite for city living means 24/7 power demand And they cant rely on combustion for heating, cooking, light and transportation they'll need electric power and that's either gonna come from FOSSIL or Nuclear. Your choice. A GRAM of uranium produces 17 times more energy than a ton of wood.


Why are metals so separated in the Earths crust? I find it very surprising that metal ore deposits are so separate, and unevenly separated on the Earth.

I do understand that there were various different conditions at some point in time in the places where ore deposits emerged, and the places were somewhat randomly distributed.

But how is it that there so many different conditions happening that all have fundamentally different effects? I would expect many different conditions, that can be grouped in much fewer types regarding the practical effect of the condition.

Or is exactly that the case, and what is surprising is only the numbers involved?

There are active geological processes that lead to separation of mineral constituents. A source material that contains specific primary minerals, with some transport mechanism (eg convection or liquid flows) to physically separate them and 'trapping' conditions that allow them to accumulate are all required. Processes that result in minerals being separated from the source material include  -

Magmatic - (within molten and partly molten magmas). Differential melting will allow specific minerals to melt and be squeezed out separately. Differential crystallisation will allow some minerals in a mixture to crystallise within a molten mass and (with changing temperature and/or pressure) to separate and reform as crystals and precipitate separately in more concentrated form in sediments at the base of a molten mass (or to rise where they are lower density than the surrounding material). Some materials can separate in their molten state, because they are immiscible (they don't mix or dissolve within each other), with similar separation because of differing density or pressure squeezing them out and solidify in concentrated forms.

Hydrothermal - minerals dissolving (usually in association with salts), with different temperature and pressures dissolving minerals preferentially. As liquid they can travel and come into contact with other minerals, resulting in chemical reactions, with potential for further differentiation.  Similar to differential crystallisation in magmas, specific minerals will crystallise and precipitate differentially out of concentrated water based solutions. Lots of sulphide mineral ore bodies were formed this way.

Physical process like erosion and sedimentation also separate and concentrate existing minerals.

(Answer in part from Wikipedia  - Ore genesis).

When the Earth was formed and was still in a molten or semi-molten state, the heavy metals, principally iron and nickel, were attracted by gravity to the Earth's deep interior, leaving only traces of them on the surface. However, the bombardment by comets, asteroids and mega-meteorites continued after a crust was formed. These were of varied composition and dumped their cargoes of metals randomly across the globe.

In addition to this, volcanoes spewed metal-rich magma into the upper layers of the crust, again rather randomly, and hydro-thermal seepages brought up metals from the depths and deposited them in the rocks on or near the surface. Magma plumes originating far down in the mantle can carry various elements, including metals, up to the surface. It often happens that metals which are close to each other in the periodic table and have similar properties are deposited in the same place.


Origin of Andaman and Nicobar islands Are Andaman and Nicobar islands in Indian ocean a continuation of Alpide-Himalayan orogeny or are they volcanic in origin?

The Andaman and Nicobar Islands are neither orogenic or volcanic in origin. They are in fact an accretionary wedge, i.e. an accretion of sediments and oceanic crust "scraped" from the subducting Indian plate. See for instance the description in the first chapter of the aptly titled The Andaman–Nicobar Accretionary Ridge:

  The islands are an exposed segment of the accretionary wedge (outer arc) of the Sunda subduction system, where the Indian Plate subducts beneath the Sunda Plate. Ongoing uplift of the sediment-dominated accretionary wedge has exposed, over a relatively small area, a diverse range of rock types associated with the subduction complex (dismembered ophiolites, volcanic-arc rocks, trench-slope deposits, submarine fan turbidites, pelagic sediments and the sediments of shelf and reef environments), making it an ideal area for investigating subduction processes.

(Unfortunately, other chapters with more detailed descriptions are not open access.)

Note that if some of the sediments are indeed volcanic in origin, it does not mean that volcanism is responsible for building the archipelago, like it was for the Chagos-Laccadives ridge for instance, to stay around India. It is the accretion of sediments in the subduction trench, and their subsequent uplift above the sea, that created the islands.

The Andaman and Nicobar Islands are partly volcanic in origin. This volcanism is caused by the subduction of the Indo-Australian Plate beneath the Burman Plate, which is an extension of the much larger Sunda plate to the east. This produces large scale volcanism throughout the Indonesian Archipelago as well as the Andamans, but is too far away from Borneo to induce volcanism there. The subduction also has a lifting and thickening effect on the margins of the upper plate, which assists in the process of raising islands and mountains. The most active volcano in the Andamans is Barren Island.


Where did all the CO₂ come from that was deposited as coal during the Carboniferous? During the Carboniferous, vast deposits of coal (or peat at that time) were created because – as far as I understand – decomposition of wood (white rot?) was not yet "invented" at that time.  This means CO2 and finally carbon was being removed from the atmosphere by photosynthesis and hence removed from the carbon cycle.

This must have led to a depletion of CO2 in the Carboniferous atmosphere because the deposition of peat lasted for quite some time.  And even today with wood decomposition, in the north summer the levels of CO2 are dropping as the Keeling curve is showing.

Was there enough CO2 in the atmosphere to support peat deposition over such a long time?  Or was there some refuel mechanism like vulcanism or some other process(es)?

Prior to the carboniferous period, and until the human industrial era, the majority of carbon dioxide in the atmosphere was due to volcanoes.

  For billions of years, geological processes like volcanic eruptions controlled the carbon concentration in the atmosphere, as volcanism is the major way that carbon rises from the mantle into the atmosphere. Most of the carbon stored in the mantle is in the form of carbonate (a salt of carbonic acid), but there are also huge stores of actual carbon dioxide sequestered deep within the mantle as a dissolved gas within the liquid rock.

  We can measure the degassing of Mt. Etna extremely well, and find that it adds about 16,000 tons of CO2 to the atmosphere each day, or 5.8 million tons per year. This might not sound impressive, but it's only one volcano. Interestingly, it's not just smoking, actively erupting volcanoes that emit CO2, but seemingly inactive volcanoes around arcs and rift zones. Persistent degassing still occurs around a great number of volcanoes worldwide, on a continuous basis.

The CO2 which formed the Carboniferous coal deposits came from the atmosphere. That's the only place it could have come from. Wood rotting organisms were in existence at the time, but the various vegetable matter which formed coal, mainly wood, formed a kind of peat which preserved it in anoxic and slightly acidic conditions. This is why you get well preserved human bodies thousands of years old in European peat bogs. Tollund Man, from Denmark, and Pete Marsh, from England, are well known examples.

This peat layer from dead trees built up over many centuries to form a peat marsh many metres thick. This was then buried and compressed by sediments and under great pressure over millions of years became coal. Coal and hydrocarbons were not the only things that devoured CO2 in vast quantities. The carbonate rocks, mainly calcium carbonate (limestone) did so too. So yes, there was enough CO2 in the atmosphere to support peat deposition over millions of years, with plenty to spare for limestone deposition as well.


What place on Earth is closest to the Sun? What is the location on Earth that is closest to the Sun?

I've seen this question asked many times, and answered in varied and contradictory ways:

The most common answer is “the summit of Chimborazo volcano in Ecuador”. This volcano is the point on Earth's surface that is furthest from the center of Earth, and that is then equated to being the closest to the Sun.
This is very commonly spoken of around the Chimborazo volcano area and among the people involved with tourism there (here is an example of this answer)
Others argue that it is Cayambe volcano in Ecuador, it being the highest point along the equatorial line (answer example).
Others say Mount Everest in Nepal/China because it is the highest point on Earth (example).
And others argue it is Sairecabur volcano in Chile/Bolivia, because it is the highest point at the latitude which is closest to the Sun on January 5th, when the perihelion happens (i.e. the point in Earth's orbit that is closest to the sun) (example).
A fifth answer, with the same logic as the previous, is Licancabur volcano in Chile/Bolivia, which quite as close to the latitude of the perihelion but is significantly higher than Sairecabur.

What is the correct answer and why?

What place on Earth is closest to the Sun?

This is an interesting question, but it lacks a key factor that is crucial to the answer: TIME.

The point on Earth closest to the Sun varies through time, so the question can be asked about any moment in time, or over periods of time. Let's analyze the factors involved.

At any given moment in time, the point on Earth's surface that is closest to the Sun is what is called the “subsolar point”. This point corresponds to the point on the surface that intersects the imaginary line that connects the center of the Earth to the center of the Sun. In other words, the subsolar point correspond to the point on Earth surface where the sunlight hits the Earth perpendicular to the ground, therefore, a vertical object would project no shadow.

(image from Wikipedia: subsolar point)

The longitude of the subsolar point corresponds to that of the meridian experiencing solar noon. Over Greenwich (longitude 0°) that happens at the actual noon, and as the Earth rotates 15° every hour, that will happen one our later (at 13:00 h UTC) at longitude 15° W, two hours later (at 14:00 h UTC) at longitude 30° W, and so on. In general terms, you can use the following formula for the subsolar point longitude ($\text{SSP}_{\text{long}}$).

$\text{SSP}_{\text{long}} = \left(\text{UTC} -12\right)*15°$

This is a simplified formula, but accurate enough for our purpose. Let's take as an example the following date

July 20, 1969, at 20:17 UTC

In that moment, the longitude of the subsolar point was 124° 15' West:

$(20+(17/60)-12)*15°=124.25°=124°15'$

Finding the latitude of the subsolar point is a bit more complicated, we need to know the declination of the Sun. Declination is the equivalent of latitude for celestial coordinates. For that, use a formula, a table, or a online calculator like the NOAA Solar Position Calculator.

Just enter the date, and even that the location doesn't matter here, we need to select “Enter Lat/Long -->” to be allowed to enter the offset to UTC as 0, otherwise the time won't be interpreted as UTC time.

From there we can find that the solar declination for our example date is 20.58° (20° 34') which corresponds to the latitude of the subsolar point: 20° 34' North.

Therefore, on July 20, 1969, at 20:17 UTC, the subsolar point was at 20° 34' N, 124° 15' W, which is somewhere between Mexico and Hawaii. That was the point on Earth closest to the Sun at that moment.

Now, what would happen if there were a very tall mountain close to the subsolar point? Would that mountain be closer to the Sun?

The answer is: probably. It depends on how far and how much higher it is relative to the subsolar point.

We can do a quick calculation based on the following diagram (in this approximation we assume that Earth is spherical, that the sun is infinitely far away and other simplifications)

From there we have

$r-r'=\Delta H$

$D = r ~ \theta$ ($\theta$ in radians)

$\frac{r'}{r}=\cos(\theta)$

After some algebra you can write that the extra height $\Delta H$ needed to be as close to the Sun as the subsolar point is

$\Delta H = r \left(1-\cos\left(\frac{D}{r}\right)\right)$

Where $D$ is the distance and $r$ is Earth's radius (in this case makes sense to use the equatorial radius of 6378.1 km)

If we plot this equation we get the following

(the vertical axis is logarithmic)

We can see that around 10 km away from the subsolar point, ~10 meters are enough to be closer than it to the Sun. ~30 meters at 20 km, ~800 meters at 100 km, ~3,000 m at 200 km, and if you go further than 340 km, not even Mount Everest will get you closer to the Sun.

So, the closest point to the Sun will be whatever geographical feature that maximizes the value $\text{Altitude}-\Delta H$, where $\text{Altitude}$ is the altitude of the geographical feature. Let's call that point “proxisolar” point. I just made up that name, but it will be handy for the following discussion.

Now that we understand the basis to establish what is the closest point to the Sun at a given moment, we can tackle the question that probably most people meant when asking this question:

What is the point on Earth that gets closest to the Sun over a year?

The most important fact to keep in mind, is that the variations of the distance between the Earth and the Sun over the year dwarf any topographical feature and even the diameter of the Earth itself. Earth’s distance from the Sun (center-to-center) varies from 147,098,074 km at perihelion (closest) to 152,097,701 km at aphelion (most distant). Therefore, the difference is 5 million kilometers!.

The perihelion happens around January 4th, when the solar declination is about -23°, therefore, the latitude of the subsolar point is around 23° South. That rules out Chimborazo, Cayambe and Everest, because they are too far to be the “proxisolar” point. In contrast, Sairecabur (5,971 m at 22.72° S) and Licancabur (5,916m at 22.83° S) are reasonable contestants.

The problem is that the perihelion happens on different days of the year and at different times of the day every year, so the point that gets closest to the Sun on a given year is just the one that happen to be the “proxisolar point” at the time of the Perihelion.

People who argues that Sairecabur or Licancabur are the points that get closer to the Sun, are implicitly assuming that the distance Earth-Sun doesn't vary much during the day of the perihelion. Therefore, the extra elevation of these mountains allows them to get closer to the Sun during that day. Unfortunately, that assumption is completely wrong. Let's see why:

An approximation of the distance Earth-Sun can be obtained from the following formula

$d = \frac{a(1-e^2)}{1+e \cos\left(\text{days}\frac{360}{365.25}\right)}$

Where $a$ is the semi-major axis of Earth's orbit, $e$ is the eccentricity, and $\text{days}$ is the number of days elapsed since the perihelion. To see the simplifications behind this equation look here (note that the conversion factor 360/365.25 is erroneously inverted in that link, thanks @PM2Ring for spotting that).

If you solve the above equation for the perihelion and for one day before/after it, you will get that the difference is 358 km, and for half a day you get 89 km. Therefore, if the subsolar point happens to be on the opposite side of the Earth than, let's say, Licancabur volcano, this volcano would need to be 89 km higher that the subsolar point to get closer than it to the Sun that year. 89 kilometers!

Therefore, we can discard the idea that a given mountain could be the point that gets closer to the Sun on EVERY year.

If we plot the above equation with distances relative to the perihelion we get the following (using $a$ and $e$ from here)

Here we can see, that if the perihelion happens a bit more than 3 hours before or after the solar noon at Licancabur, the ~6,000 m of elevation advantage would not be enough to get closer to the Sun than the subsolar point at the perihelion, even if such point is at sea level.

Note that three hours corresponds to 45° in Longitude, which at that approximate latitude corresponds to approximately 4,600 km.

Therefore, it can be argued that Licancabur is the point on Earth that has more chances to be the closest to the Sun in an arbitrary year. But in a given year, it might or might not be the closest depending on where the subsolar point is at the moment of the perihelion.

Finally, it is important to note that the distance Earth-Sun at the perihelion varies widely from year to year. If you look at this table of perihelions between years 2001 and 2100, you will see that perihelions often vary by several thousand of kilometers.

Therefore, for example between years 2001 and 2100, the closest perihelion by far is the perihelion of next year (2020), and it will happen when the subsolar point is in the middle of the Indian ocean, about 12,700 km away from Licancabur and Sairecabur volcanoes. Therefore, the point that will be closest to the Sun this century will be one in the middle of the Indian ocean about 320 km south of Rodrigues Island.

Said this, the question of which point on Earth will get closest to the Sun depends on the period of time on which it is considered. For each year, each century and any other arbitrary period of time, the answer will be different.

At any one specific moment the subsolar point is the point on Earth that is closest to the Sun at that specific moment.

The subsolar point on a planet is the point at which its sun is perceived to be directly overhead (at the zenith);[1] that is, where the sun's rays strike the planet exactly perpendicular to its surface. It can also mean the point closest to the sun on an astronomical object, even though the sun might not be visible.
To an observer on a planet with an orientation and rotation similar to those of Earth, the subsolar point will appear to move westward, completing one circuit around the globe each day, approximately moving along the equator. However, it will also move north and south between the tropics over the course of a year, so it is spiraling like a helix.
The subsolar point contacts the Tropic of Cancer on the June solstice and the Tropic of Capricorn on the December solstice. The subsolar point crosses the Equator on the March and September equinoxes.
When the point passes through Hawaii, the only U.S. state in which this happens, it is known as Lahaina Noon.[2]

There is a minor exception to this rule.
The subsolar point can be defined as a mathematical point, so that someone could theoretically be standing with their body over the exact mathematical subsolar point and with their two legs and feet on either side of the exact mathematical subsolar point.
Thus a place that is close to the the exact mathematical subsolar point and at a higher altitude than it might be closer to the Sun than the exact mathematical subsolar point.  The farther away from the exact mathematical subsolar point a place is the higher its altitude must be in order to be closer to the Sun than the exact mathematical subsolar point.
Earth has an polar radius of 6,356.8 kilometers and an equatorial radius of 6,378.1 kilometers, so a place at the equator is 21.3 kilometers farther from the center of the Earth than a place at one of the poles, not allowing for minor variations in the figure of the Earth and not allowing for altitude differences.
The subsolar point of earth is never farther north than the Tropic of Cancer and never farther south than the Tropic of Captricorn, and so in recent times is never North of about 23 degrees 26 minutes North Latitude or south of about 23 degrees 26 minutes South Latitude.
Of the points mentioned in the question Chimborazo and Cayambe Volcanoes in Ecuador, and Sairecabur and Licancabur Volcanoes in Chile, are within the tropics and thus can sometimes be the subsolar points, while Mount Everest is north of the Tropic of cancer and can never be the subsolar point.
If Earth as a radius of 6,356.8 to 6,378.1 kilometers, it must have diameter of 12,713.6 to 12,756.2 kilometers, and thus at any one moment the subsolar point, wherever it is at that moment,  will be about 12,713.6 to 12,756.2 kilometers closer to the Sun than the point that is farthest from the Sun, wherever it is at that moment.
The semi-major axis of the orbit of the Earth is 149,598,023 kilometers, which can be taken as the average distance between the Earth and the Sun. Whenever the Earth is exactly 149,598,023 kilometers, the subsolar point will be about 12,713.6 to 12,756.2 kilometers closer to the Sun than the point that is farthest from the Sun.
So at any moment when Earth was exactly 149,598,023 kilometers from the Sun, and the subsolar point happens to be 12,756.2 kilometers closer to the Sun than the point on Earth farthest from the Sun, the difference will be 1 in 11,727.475, or 0.0000852 of the distance between the Earth and the Sun.
The perihelion distance between Earth and the Sun is 147,095,000 kilometers while the aphelion distance between Earth and the Sun is 152,100,000 kilometers, a difference of 5,005,000 kilometers. Since it takes earth about half a year, or about 182.625 days, to go from Aphelion to perihelion, the distance between Earth and the Sun changes by an average of about 27,405.886 kilometers per day.
Thus any point on Earth, even the point on Earth that is farthest from the Sun, at the exact moment of perihelion should still be closer to the Sun than any point on Earth, even the subsolar point, on any other day of the year.
What about astronauts in orbit, bound by gravity to the Earth?  Do their capsules and space stations count?  Whether or not space capsules and space stations count as part of Earth, some astronaut in Earth orbit might have been closer to the Sun and another astronaut might in earth orbit have been farther from the Sun than any human in history.
And what about Apollo astronauts who traveled to the Moon and orbited or passed beyond it?  Does the Moon count as a place on Earth since it is bound to Earth by gravity?  And even if not, some Apollo astronaut or astronauts must have been farther from Earth than any other humans.
The Apollo missions all lasted for at least a quarter of a lunar orbit around the Earth.  The landings on the Moon were all on the near side of the Moon that faces the Earth, and all during the Lunar day, which means that the near side of the Moon must have been facing the Sun and thus farther from the Sun than Earth during the missions.
Earth is at perihelion, closest to the Sun around January 4, and at aphelion, farthest from the Sun, around July 4.
So of the manned missions that reached Lunar orbit, Apollo 11, July 1624, 1969, and Apollo 15, July 26-August 7, 1971, were closest to aphelion about July 4, and so their astronauts might have traveled farther from the Sun than any other humans, depending on where the Moon was during its orbit.
And Apollo 8, December 21-27 1968, Apollo 17, December 7-19 1972, and Apollo 14, January 31-February 9, 1971, were closed to perihelion about January 4.  And so the astronauts in one of those missions might have come closest to the Sun of all humans.  But I doubt that.  Probably some astronaut(s) who orbited the Earth several times on a January 4 passed close to a point above the subsolar point at a time very close to perihelion and came closed to the Sun - or least far from it - of all humans so far.


When will glaciation resume? Has global warming delayed return to global cooling? As far as I understand, we are currently living in the Holocene, an interglacial period of the Quaternary glaciation, i.e. the current ice age that has so far lasted 2.6 million years. The Holocene began about 12,000 years ago. While humans emerged about 200,000 years ago, human civilization is almost entirely coterminous with the Holocene.

Questions:

(A) Are there any generally accepted estimates for how long the Holocene will last?

(B) Is anthropogenic global warming delaying the return to glaciation?

First, great question, though answers are likely to be non specific and speculative.

  As far as I understand, we are currently living in the Holocene, an
  interglacial period of the Quaternary glaciation, i.e. the current ice
  age that has so far lasted 2.6 million years. The Holocene began about
  12,000 years ago. While humans emerged about 200,000 years ago, human
  civilization is almost entirely coterminous with the Holocene.

As others have said, defining our current period as the Holocene is iffy.   Human influence is pretty huge, and perhaps, even as many as 6,000-7,000 years ago the growth of the agricultural revolution, some farm animal domestication and early, though much smaller, deforestation may have played a role in climate, at least, I remember reading that, though a quick google didn't provide a good source, but I've read that.   It's probably not consensus though, just some people's opinion.

  (A) Are there any generally accepted estimates for how long the
  Holocene will last?

So, how long?   There's 2 very different answers to this.

First one, if we take out the human effect, or, lets say, in the relatively near future we "fix" our CO2 and other human effects on the planet and return the Earth mostly to how it was.   Then the answer is kind of simple, we just Look at past warm periods and make an estimate from those.

Without human activity the Holocene would very likely be just another inter-glacial warm period between ice ages in the continuation of the Quaternary with a similar length of time.  See chart:, If the average length of inter-glacial warm period is about about 20,000 to 40,000 years we can just subtract 11,000 from that and reach a rough estimate.

Or, if you want more accuracy, you can look closely at the 3 orbital cycles and calculate based on that - but I'm not going to do that as it would get more complicated.  More on that here.

It's also likely that there would be a cooling period within that time-frame.  We can see cooling, like the little ice age, without it being an actual ice age.

  When will glaciation resume? Has global warming delayed return to
  global cooling?

  (B) Is anthropogenic global warming delaying the return to glaciation?

First, it's worth pointing out that returning to global cooling and a return to glaciation aren't entirely the same thing.   If, lets say, we continue our CO2 footprint/production and reach 450 PPM before we cut back enough to level off for a few decades, then, cut back enough to see the oceans gradually take in CO2 and reduce the levels in the air, we could see a gradual global cooling within 100 years or so - maybe, provided the higher ocean temperatures and Albedo drop due to loss of ice cover didn't created a new equilibrium.   But in general, the earth can go through cooling periods without glaciation, so those 2 questions are similar but not entirely the same.

But in general, calculating glaciation with the human factor, it's a much harder question, especially since we can't see the future and how high CO2 levels will get.

Modern ice ages are defined as an advancing glaciation across a significant range of the Northern land, which, as pointed out above, coincides well with Milankovich cycles, but to actually have that happen, you need a few things in place.   Milankovich cycles don't cause ice ages all by themselves, cause they were there during non ice ages too.

The modern ice age cycle only started about 2.6 million years ago and it is thought to have been brought about by the formation of Isthmus of Panama about 5 million years ago, which separated a current between the Atlantic and Pacific Oceans which helped the arctic ocean cool and freeze over.  Shortly after that Isthmus formed, the Earth began to cool.   See here (chart from Milankovich link above).

Modern ice ages also coincide with falling CO2 levels, and while the CO2 drop follows the temperature drop, there's a reason for that.  Colder oceans hold more CO2, so the Atmospheric CO2 drops when temperature drops.  This serves as a feedback loop where cooling leads to more cooling and that's part of why ice ages are as big as they are.   Albedo is another feedback loop, so the trigger to get an ice age started is actually pretty small.   The Orbital cycles of the Earth are thought to only contribute about 1 degree of cooling in and of themselves and the other 9 or so degrees of global cooling between peak ice age and average Holocene is thought to be caused by these feedback mechanisms, primarily albedo and drops in atmospheric CO2.

So, there's 2 questions to ask as to whether man made global warming will prevent the next ice age and perhaps future ice ages.   We know that the Milankovich cycles will continue, but will CO2 be low enough for the cycle to lead to glaciation, and, how fast will CO2 levels drop, so, over the next 10,000 - 30,000 years.    Nobody knows the answer to those questions.

Looking at the last 800,000 years or so, based on ice-core samples, warm periods between ice ages you usually have about 260-280 PPM and peak ice age periods, about 180-200 PPM CO2 with the ranges in between, mostly during transitional periods.  When these changes occur, most of the CO2 is believed to be absorbed into or released from the oceans, though I see no reason why a smaller portion of the change couldn't be driven by changes in living bio-mass corresponding to the changes in temperature, ocean size and grow-able land area.

By burning fossil fuels, we've added carbon that was effectively removed from the Carbon cycle. For a rough calculation for how much, every year we add a bit over 30 billion tons of CO2 by burning fossil fuels every year.

The Atmosphere, at 270 PPM with a mass of the Atmosphere, about 5.148 x 1018 KG is about 2,320 billion tons.   Since the industrial revolution, CO2 PPM has increased to about 400 PPM, which is an increase of about 1,030 billion tons (atmosphere only) with roughly about 400 billion tons (rough estimate), having been absorbed into the oceans.

Oceans are estimated to store about 50 times the CO2 than the Atmosphere, Source, so assuming that's accurate, Oceans currently store over 110,000 billion tons of CO2 and since the industrial revolution, we've added (ballpark) 1,400 billion tons from burning fossil fuels - about a 1.2 - 1.3% increase to the total CO2 in the Oceans, Air and Land-biosphere.   That's the crux of the question, what effect will that have.

Over enough time, like, 10,000-30,000 years when the next ice age might be due, the oceans could absorb most of the atmospheric CO2 and the effects could be fairly small.   But as the Earth warms and Oceans warm and warming oceans increases the Atmospheric CO2 cause oceanic absorption drops.  With warmer oceans there will be a new equilibrium and with that in mind, it's entirely possible that the new atmospheric CO2 equilibrium, if left to it's own devices, might already be sufficient to prevent ice ages for a long time, perhaps a few hundred thousand years.

Predicting atmospheric CO2 levels 10,000 to 30,000 years from now, for all practical purposes, impossible, and that's what we'd need to know to estimate if we've stopped the next ice age or not.   What we have done is increased the amount of CO2 in the biosphere of earth by about 1.2–1.3% and since we continue to burn fossil fuels, we're likely to have created an increase of 2% before alternatives are in place, perhaps a bit more than that.

All of this, however, is probably irrelevant, cause we have some ability to trap CO2.   It's not easy, but we can do it and if, as our technology improves and we begin a gradual CO2 trapping program, we could re-start the next ice age in 10,000 years or so, assuming that's what we want to do.   Now, I don't mean to make light of the CO2 problem cause we appear to be facing very big and real issues over the next 20-50-100 years and that's much harder to avoid at this point, but over 10,000 years, we could probably fix our CO2 situation and bring the Earth back into the ice age cycle, or, we could use CO2 to avoid future ice ages if that's preferred.  Collecting and trapping 1–2 trillion tons of fossil fuel generated CO2 isn't easy and we don't have nearly the technology to do that today, but over 10,000 years I feel pretty confident that we could be able to do it, provided we keep progressing technologically.

A) Some would argue that the Holocene is over, and we are now entering the 'Anthropocene', a new era hugely impacted by human activities. Another view is that the Holocene will be over when the polar (including Greenland) ice reaches a new equilibrium state - which is not in the foreseeable future.  Technically there is no way to predict the 'official' end of the Holocene.

B) Major glaciations are somewhat infrequent in the history of planet Earth. There have only been about 7 +/-1 glaciations, depending upon how you define 'major'. The current glaciation is about over, and human induced global warming will see to it that we are not just entering a mere inter-glacial interlude. On top of human induced global warming there is another very long-term global warming caused by the sun's changing radiance. Since the mid pre-Cambrian the sun's composition has changed from less hydrogen to more helium, which has increased the sun's energy output by about 20 to 25%. This change will continue at a slow but accelerating rate, such that the the planet is getting progressively warmer, and we will never again see another major glaciation on planet Earth.


Are there any differences between the subalkali and alkali rock occuring tectonic environments? Here question ends. Beyond details exist

Do they occur on the same tectonic regime?
For a start to distinguish Subalkali rocks froms Alkali rocks,
my knowledge says that mantle is the source of Alkali rocks. Ocean Island Basalts are Hawaii, Reunion etc are all Alkali rocks. Large ignous provinces are also sourced from mantle by the mantle plumes. Such as Deccan, Siberian traps.

But in Robil Gill's ((Gill, R. (2010). Igneous rocks and processes: a practical guide. John Wiley & Sons.)) book on page 291, (chapter 9-Alkali rocks) says that Most of the large igneous provinces are subalkaline and they are much bigger and more frequent than the Alkaline Large igneous province. From this i derive that LIP's can be subalkaline.

So are there any difference between subalkali and alkali rock occuring tectonic environments ?

Yes, there are many differences and subdifferences and nuances.

I will try to keep it in simple terms which will satisfy your question.

Alkaline magmas form by low degree partial melting of the deep mantle. This is why you see them in hotspots. It's very hot down there, but you do not form a lot of melt. For example, the amounts of melts in Hawaii are negligible compared to what you have in large igneous provinces (think Deccan Traps) or mid ocean ridges. Another tectonic setting with common alkaline magmas are rift zones. The best example is the east African Rift (Ethiopia, Kenya, etc). Again - deep melting of the mantle leads to alkaline magmatism.

Subalkaline magmas form in shallower melting. For example, the voluminous mid ocean ridge basalts are not alkaline, and the melt forms within a few kilometres of the surface. Arc magmas (andesites etc) are also not too alkaline because they form by fluid-assisted melting of not too deep mantle above subduction zones.

Even though large igneous provinces form by mantle plumes, the melting so extensive that the melts are not alkaline any more. To get alkaline melts, it has to be low-degree partial melt.

I can't put it as a comment so it'll have to be an answer this time around.

Either way, I remember doing chemical analysis and my professor at the time was very adamant that yes, there is a difference depending on tectonic setting. Alkaline magma series tend to be present in convergent configurations, however, it's not exclusively found in these. To be honest, the question is a bit too broad to be summed up here but use it as a rule of thumb, according to my professor. However, subalkaline series are present in most plate settings.

There is a lot of interaction going on with magma from the mantle reservoir during its ascent through the crust which could be a source of contamination after all.


Could burning all fossil fuels (available on earth) render the atmosphere unbreathable? What if humanity burns all fossil fuels it can find? Putting the negative effects of climate change aside, would the enormous amount of $\small\mathsf{CO_2}$ in the atmosphere eventually make it unbreathable?

Not directly.  What possibly could happen is that rising temperatures turn the parts of the ocean anoxic, which leads to large releases of hydrogen sulfide, which is toxic: https://www.chemistryworld.com/news/ocean-chemistry-changes-triggered-earths-greatest-extinction-event/2500368.article

No. For a start, humanity will not burn all the fossil fuels it can find. But let's suppose for the sake of argument that humanity recognises no restrictions and fulfils all its energy needs by burning fossil fuels. Only a limited amount of fossil fuels are recoverable; the vast majority will have to stay in the ground.

Oil, for example, won't suddenly run out. What would happen is that it would gradually become scarcer, and increasingly expensive to recover. Eventually it would become too expensive to burn, so humans would have to turn to other fossil fuels, coal being the obvious one. Some would be used to make synthetic oil, and some burned in its natural state. The world has very large recoverable reserves of coal There could be enough to last humanity for a thousand years, but eventually recoverable reserves would become so scarce that it too would become too expensive to burn and, like oil, would be used as a source of chemicals and plastics.

All these fuels together, oil, gas and coal, might conceivably be burned for 2,000 years before becoming too scarce and expensive to be used as fuels. During that time,plants,especially in the oceans, would not be idle. Much of the CO2 generated would be sequestered by natural means, and although there would be a big rise in atmospheric CO2 with consequent climate warming, it wouldn't be nearly enough to make the atmosphere unbreathable.


Thermal expansion of Earth Matter tends to change its volume in response to changes in temperature--or, hot things tend to be expanded. Is the thermal expansion of Earth significant?

That is, is it significant when compared against a cooler or perhaps internally-inert Earth?

Here's a take on calculating earth's thermal expansion and shrinking, under certain assumptions mentioned in the text. It seems to me, from a short overview, that the core is assumed to be constant over the time. It focuses on the mantle part of the earth, its mineral phases and convetion. Take it with a grain of salt:

https://www.sciencedirect.com/science/article/pii/S167498711200148X

tl,dr: after consolidation, earth's radius was 120km larger than today. It shrank by 110km in a few million years, then expanded a bit (11km), then contracted by 8km, and subsequently contracted by around 12km to the present day.

If they say so :-)

There is no thermal expansion of the Earth. On the contrary, the Earth is very gradually cooling, and therefore shrinking, but so gradually that the effects are imperceptible and perhaps in the short term unmeasurable. You can see the process at work on Mars, which has over the course of 4.5 billion years lost much of its internal heat owing to its smaller size and greater distance from the sun. The result is that volcanism has ceased and the planet has a much thicker crust, but the core is still molten. Therefore Mars must have shrunk a little, but we don't know exactly how much because we have no precise measurements from four billion years ago.

Gravitational flexion ie. tides in the Earths outer regions caused by the moon, as well as decay of radioactive elements in the core and mantle, generate heat which reduces the rate at which the Earth cools. The Earth's loss of heat is so gradual that its interior still won't be completely inert when the sun expands to become a red giant in 5 billion years time. The Earth will then stop cooling and the surface will be scorched and probably melted, but it's nothing to worry about because 5 billion years is an almost unimaginably long time. Humans will have gone to join the dinosaurs billions of years earlier.


Is the maximum human population carrying capacity of Earth higher or lower than the current total human population? Not sure if this is the right stack for this but:
I have been arguing with friends on overpopulation, several are convinced that Earth cannot sustain the current population.  Without getting into all of the ways that we are destroying various ecosystems and polluting, I believe that if we were actively working to optimize the environment and how we use resources, Earth could easily handle many, many more humans.
Such as renewable energy, reducing waste, committing to reversing desertification, and so much more.  But regardless of the behaviors we specifically change, looking at the raw chemistry of the planet, i.e. how much water, oxygen, carbon, plant life, and so on, there is some maximum amount of humans that can live healthy lives.

The FAO estimate that we use 11% of the Earth's surface area for agriculture,  and that that represents approximately a third of the land that 'could' be used (http://www.fao.org/3/y4252e/y4252e06.htm). If we accept that current agricultural production is at a level that allows the current population to live healthy lives that implies that we could triple our population and not starve.
In this very simplistic view I am ignoring the very real questions of inequity in distribution, what constitutes 'healthy' and the potential of changing efficiency in agriculture or transitioning populations away from expensive meat based diets.
However, and it's a really big however, you couldn't make that sort of increase in the area of globe used for agriculture without destroying natural ecosystems, and it's arguable that already much of global agriculture is unsustainable in it's present form, as aquifers are overexploited and soil quality degrades.

The population is degradatively and unsustainably overconsuming
Everyone truthful agrees the above statement.
The keywords are degradatively and destructively for people and crowds. Few people deny that.
The seas are already being overfished with many species collapsed to low volume stocks, the land is intensely overfarmed with cocktails of chemicals and pesticides, the rivers near industrial farms also absorb nitrogen and pesticides, the sky is destabilized, deforestation is impissible to control. Dolphins tigers rhinos birds insects etc are now extinct, and 80 percent of the world population want to increase resource consumption to 500% of current levels, i.e. young Africans want playstations, SUVs... in a reasonable compromise we cant responsibly manage current overpopulation, its very poor on average, so from a responsible point of view, having children are being born in poor megacities, uneducated and thirsty to have a house garden and car. Its destructively overpopulated without and end to the degradation predicted.


If water is a renewable resource, why is there water scarcity? Water is a renewable resource, renewed by the water cycle.

If we use water too quickly, water should get evaporated and come down again as precipitation.

So, Why is there water scarcity if water is a renewable resource?

What I miss in the other answers is water quality.

Even is there is sufficient water available it is often of insufficient quality  for the purpose you want it for:

We often don't drink straight out of rivers
We don't irrigate with salt water

etc.

So you need to spend effort to prepare it for use. This adds to the experience of shortage.

1)You have to consider the source of water for each location. Groundwater, for example, is a fairly abundant but non-renewable water source in some locations. It can take a centuries to replenish.
2)River water fed by mountain glaciers depends on the size of the glacier, as the glaciers shrink, meltwater decreases.
3)Regions that depend on rainwater or snowmelt can experience water shortages when there's a low-snow winter or drought.
Even is there is sufficient water available it is often of insufficient quality for the purpose you want it for
We often don't drink straight out of rivers
We don't irrigate with salt water
This adds to the experience of shortage.


Mega-tsunami, what is the greatest possible height of a tsunami? The notion of a taller-than-skyscraper, so called "megatsunami" is not new - with the often-reported 524m (1720 feet) high Lituya Bay tsunami of 1958 is sometimes referred as such (despite the wave not reaching that high). In many movies (and some documentaries), there are massive tsunami depicted. Some of these movies depict tsunami taller than skyscrapers (such as in Deep Impact and Haeundae). There is also evidence of massive tsunami occurring in different places around the world in the past.

We have seen the reality of devastating tsunami in and around the Indian Ocean in 2004 and Japan in 2011 for example.  These, while not being 100's metres high, are still catastrophic.

How a tsunami forms and how it travels is well documented (thus is not the subject of this question), nor is this asking about the inland reach of such a disaster, they are answered in the related questions Is a mega tsunami that will destroy America inevitable?, Is Atlanta too far inland and too far above sea level to be affected by the comet in “Deep Impact”? and Why does every tsunami travel differently?. But rather, the maximum height possible for a tsunami from any cause.

Is there a theoretical upper limit for the maximum height of a tsunami?

Your question seems to lump at least three different phenomena together: tsunami waves(seismic sea waves), the effects of landslides near the coast, and the effects of asteroid impact into the ocean.  You might have also included rogue waves. Each of these are complex phenomena when you start considering 'realistic' boundary and initial conditions - so you should not expect a highly accurate answer from a simple model.

Seismic sea waves, or waves initiated by land slide, can travel great distances across the ocean. These waves have a long wavelength and therefore may be modeled as shallow water waves. Although the height of classical shallow water wave may be limited (in theory) by the wave steepness (1:7) where the wave 'breaks' and collapses, Computer models of tsunami are likely to be much more accurate.

If you are primarily interested in what happens near a coastline or in a bay, then the most accurate solution will likely be a computer model that also include realistic boundary conditions. See these computer models of a dam break and waves in an irregular water body.

The possible initial conditions for an asteroid impact could be so large that planetary material is ejected into orbit. The Martian meteorites found on Earth are believed to have originated from a impact on Mars. In a large impact, the height of the rim wall might not be an accurate estimate of the maximum altitude material was actually thrown.

the water would reach a rim, from there it is inevitable to curve, therefore the max would be 3 kilometres due to the mass for it to be not a sheet of water, if it were to be a metre thick the water could reach 9km, if a chixclub event would occur in the pacific, even worse, a larger asteroid. maybe even reaching 10 km as it would reach the atmosphere or evaporate.


Can we really travel through earth's core? Inspired by the movie, "The Core".

Can we really travel through earth's core? I will provide 2 sub questions:

Is there any substance that can resist the heat of earth's core?
Between the crust and mantle, and the mantle and outer core is there any "wall" between them? And how hard is the wall (can we go through it)?

As Chris Mueller said, in short: it isn't, or at least highly infeasible. Projects to drill into the mantle, such as the Kola Superdeep Borehole, have all failed because drilling equipment can't withstand the heat at only ~15km deep. Even if we were to come up with some sort of cooling system that's able to cool to 6400km or 12800km deep (depending on whether you would drill from one side only or from both sides at the same time), pressure is the second barrier that holds us from traveling through the earth's core.

According to Lide (2006) the pressure in the inner core is 330 to 360 GPa, at which iron becomes a solid even at the high temperatures in the core. If you could drill as far as the core you would have to build a device that's able to withstand that pressure, because if you can't, the material surrounding your well would immediately become liquid and fill the hole, if not shoot up your well towards the surface.

There are no physical walls between the layers of the Earth, only transition zones where temperature and pressure combinations lead to different behaviour of the materials. An example is the Mohorovičić discontinuity, or Moho, which is the boundary between crust and mantle, below which temperatures are high enough and at the same time the pressure is low enough so that rock becomes either liquid or at least a "flowing" solid. Similarly, at the boundary between the inner and outer core the pressure is so high that even at those temperatures the iron becomes a solid.

Lide, D.R., ed. (2006-2007). CRC Handbook of Chemistry and Physics (87th ed.). pp. j14–13.

Nuclear reactions would be required to create a shaft. High melting point solids under the extreme pressures would be required to reinforce it.  If gamma rays can tunnel, the theory is not implausible but requires an engineering feet to put physics into practice. This should be the focus of exploration besides space exploration.


Extent of desert area influence in local climate With reference to this image...:

...from this recent tweet, I was wondering to what extent would Mediterranean regions be affected by the large desert areas to its South?

"Affected", here meaning that there would be higher correlation between temperature measurements between the Sahara and Malta (for example), than Malta and Iceland.

I suppose that measurements are correlated but that this correlation reduces with distance to some lower value (but not zero). The question here is, how quickly does this correlation tend to its lower value and is the distance between the "centroid" (?) of the Sahara desert to points in the Mediterranean short enough so that it can be considered an "influence"?

The mediterranian do in a way create its own climate and is partly protected from the north saharan desert by the dominating wind direction in the area.

The dominating wind direction is from west and northwest,The wind blows into the saharan desert in the direction of the equator in the winter,This creates the mild winters the mediterranian is known for.

In the summer more warm and dry air moves from the north saharan desert and into the mediterranian area,this creates the dry summer climate the mediterranan is known for.

So the north saharan desert have the strongest influence on the mediterranian climate in the summer.

you can read about it here https://en.wikipedia.org/wiki/Hadley_cell if you click on the animation you can see how the precipitation changes over the year and thereby also the temparature.

and here https://en.wikipedia.org/wiki/Mediterranean_climate

The proximity of the Sahara certainly does influence the Mediterranean climate, but how much varies according to which way the wind is blowing. The presence of the Sahara has a warming effect and a desiccating effect. Winds also carry large quantities of dust to the Med and to much more distant places like Latin America. Not often, but it does happen. It isn't all that rare for southerly winds from the Sahara to bring unusually warm temperatures to Britain, and to deposit dust on our motorcars. I live here, so I should know.


Water on Mars and Earth If water on Earth came from meteorites, why doesn't Mars have substantial water? What made it more highly probable on Earth than on Mars?

If water on Earth came from meteorites, why doesn't Mars have substantial water?

First off, that's a conjecture regarding the origin of the Earth's water rather than a known fact. A few times a year or so, a new journal article will appear that argues that the Earth's water is primordial, then another arguing that it came from comets, then yet another arguing that it came from asteroids.

If the Earth's water is mostly primordial, most of it is over 4.5 billion years old. If it came from asteroids or comets that collided with the Earth after the Earth had formed, it's still very, very old. Regardless of the source, almost all of the Earth's water has been here for at least 3.8 billion years old, since the end of the late heavy bombardment.

The same would apply to Mars. It has had almost four billion years to lose its water. So has the Earth; some argue that the Earth, too, has lost a lot of water to space in those four billion years.

The key causes of the disparity is that the Earth is significantly more massive and has a magnetic field. Mars's essentially non-existent magnetic field means that water molecules in the atmosphere are more readily split into hydrogen and oxygen than are water molecules in the Earth's atmosphere. Mars's smaller gravitational field means the hydrogen produced by these events has a much greater chance of escaping before it re-forms water than on the Earth.

A very recent conjecture poses another possibility, which is that Mar's mantle is slightly different in composition than the Earth's, and this different composition enabled Mars's mantle rocks to absorb significantly more water than did the Earth's.

The loss of liquid water on Mars was also due to the planet losing its magnetosphere. During the Hesperian period (about 3500 mya) the iron core stopped rotating fast enough to create a planet-wide magnetic field of the type Earth has. Because of this, the Martian atmosphere was no longer protected from solar wind, which caused it to erode away to its current (very low) density. Without enough gases in the atmosphere to generate a greenhouse effect, Mars became much colder and drier. This is why there's no liquid water on its surface at present.


Do flights affect tides? Can artificial satellite positions affect tides? on Space Exploration.SE asks if artificial satellites can affect tides, because they are a lot closer than our natural satellite, even though they are much smaller in mass.  The top answer to that question is basically "no."

A commenter estimates that Pluto might have a larger effect, but Pluto is such a distant object I didn't think most people could easily relate to that, so I tried running the numbers with something people might be more familiar with, closer to our surface: airplanes.

Let's start by considering a big plane in relatively common use.  The Boeing 747 is well known as a popular aircraft type, and it seems that the version of it they're producing now is the Boeing 747-8.  This page says it has a maximum takeoff weight of 4.48*105 kg and a maximum landing weight of 3.12*105 kg, with a service ceiling of 1.3*104 m.  I'll round that to a weight of 3.5*105 kg mass and 1*104 m height above the surface of the ocean.

Now, the moon.  Wikipedia says the moon has a mass of around 7*1022 kg and a distance from the center of the earth on the order of 4*106 km, which is 4*109 m.  Earth's radius, about 6.3*103 km, is about a tenth of a percent of that distance and lost in the rounding/simplification of the Moon's orbit to be circular instead of its actual eccentricity.

This means that the moon's mass is (7*1022 kg / 3.5*105 kg =) 2*1017 times that of the 747.
The moon's distance from the surface of the ocean is (4*109 m / 1*104m =) 4*105 times that of the 747.

Comments on this answer note that "the amplitude of tides is proportional not to the strength of the gravity force, which is proportional to r2, but to its gradient, which is proportional to r3...a factor of 103 in distance means a factor of 109 in tidal effect."  Therefore, the effect that the distance has on the amplitude would be ((4*105)3 =) 6.4*1016.

Thus the overall effect of the 747 on tides should be (6.4*1016 / 2*1017 =) about a third of the effect of the moon.  It's a back-of-the-envelope order-of-magnitude calculation, but a much larger result than I expected.

Did I mess up somewhere in the math or facts above?  (If not, I'm willing to cut & paste that content into an Answer, but for now it's just showing the work I've done in arriving at this question and attempting to solve it myself.)

Now, there are many flights in the sky at any given moment, all around the world, and to a certain extent any tidal effects of one flight would be cancelled out by the effects of one or more others.   However, the flight map is not completely balanced or evenly distributed north-south or east-west.

Do flights affect tides?

Both airborne planes and the Moon affect the tides, but the effect of airborne planes is so small as to be negligible.

From your sources the mass of a Boeing 747 ($m_{747}$) is $447.696$
$(10)^3$ $kg$.
Likewise, from your sources, the mass of the Moon ($m_{Moon}$ is
$7.347$ $(10)^{22}$ $kg$.
Typically a 747 would fly at an altitude ($r_{747}$) of around $30$
$000$ $ft$. This is close to $10$ $000$ $m$ ($10^4$ $m$).
The distance the Moon is from the Earth ($r_{Moon}$) is $384$
$400$  $km$, which is $384.4$ $(10)^6$ $m$.

Now, Newton's Law of Universal Gravitation states, $F$ $=$ ${G.m_1.m_2}/{r^2}$

Where:
$G$ is the gravitational constant, being $6.6743$ $10^{-11}$ $m^3.kg^{-1}.s^{-2}$,
$m_1$ and $m_2$ are the masses of the two objects being considered & $r$ is the distance between them.

Because tides are being considered only the mass of water is to be considered, not the mass of the Earth. To simplify things I am assuming the area of water affect by each is the same and hence the mass of water will be the same in each case.

For the Earth and Moon system, the force of gravity will be:

$F_{E-M}$ $=$ $6.6743(10)^{-11}$ $.$ $7.347(10)^{22}$ $.$ $m_{ocean}$ $/$ $[{384.4(10)^6}]^2$ $=$ $3.3186(10)^{-5}$ $.$ $m_{ocean}$

For the Earth Boeing 747 system, the force of gravity will be:

$F_{E-747}$ $=$ $6.6743(10)^{-11}$ $.$ $447.696(10)^{3}$ $.$ $m_{ocean}$ $/$ $[{(10)^4}]^2$ $=$ $2.9881(10)^{-13}$ $.$ $m_{ocean}$

Dividing $F_{E-M}$ by $F_{E-747}$ the gravitational force of the Moon is $111$ $060$ greater than that of the plane.

If the tides produced by the Moon are up to $10$ $m$, then the maximum height of a tide produced by a 747 would be around $0.099$ $mm$.

I think you should calculate the distance between the plane and the oceanic floor (instead the surface), or at least some depth. Unlike plane, the moon has almost the same gravitational influence on the surface of the oceans as in the deepest ocean trenches.

Plus, planes flies very fast and are very small objects. Oceans moves too slow, a wave can't follow each plane. No temporary effect is measurable because instantly dissipated by the waves (think about wind). The gravitational influence of the moon affects a vast part of the ocean, giving it time to react.

Oil platforms have certainly more influences, they are just above the surface, heavier, can be far in the ocean and do not move!

Planes have surely more influence on weather (due to reactors / fuel) than waves.


Is global warming being moderated by latent heat of melting polar ice? I've only had a secondary education in physics, so bear with me, but with the greenhouse effect and all, wouldn't we be much hotter already if the ice melt-rate wasn't increasing, since more (heat) energy goes toward changing state, rather than changing temperature? My understanding of latent heat is that it is the applied heat that does not result in a dramatic temperature increase, rather it is used to change state (i.e. solid ice to liquid water).

The obvious issue would be that once the ice is all melted, or it doesn't melt quick enough, we'll have proper heat problems (not just the 2 or 4 or 6 deg changes being discussed now).

Are there numbers available on this? Or is this effect nonsense? Or am I looking towards a time a few orders of magnitude beyond my years?

Latent heat is a factor, but is completely eclipsed by the rate of global warming.

For example, since 1978 the April (maximum) Arctic sea ice has decreased in volume by about $11,000$ cubic km. The latent heat absorbed by the ice to achieve this is about $3.7(10)^{18}$ Joules. Compare this to the amount of excess heat, which has been absorbed by the oceans, which is about $2.0(10)^{23}$ Joules per decade. That is, some three to four orders of magnitude more heat than the decadal heat required to melt the Arctic ice.

Of course there are complications of the heat absorbed by land (much less than in the oceans), melting of Greenland and Antarctic ice sheets, and uncertainty over the depth of oceanic warming, due to sparsity of measurements, especially in the southern hemisphere.

But however you cut the statistics, the latent heat is minuscule compared to the planetary heat imbalance.

The melting polar ice definitely absorbs a significant amount of energy,
maybe not as much as the oceans do, but critical here is that the energy
absorbed is latent energy HIDDEN heat, and does not show up on the big
thermometer, and also exhibits positive feedback, i.e., less reflection and
more absorption, Therefore the melting ice is very important and scary.

Another less talked about topic, increasing atmospheric water
vapor, another source of latent HEAT, with positive feedback, $H_2O$ is
a powerful greenhouse gas, very scary, VERY SCARY indeed.


During the "Ice Ages" or "Snowball Earth" times, where was all the energy? We often seem to accept the idea that there were periods of time in which the entire surface of Earth was frozen, for the most part. This implies that there were periods of time in which the entire surface was NOT frozen over. Thus, there must have been heat and energy present on the surface. How did all that energy move to cause an ice age? It seems absurd for all that energy to just radiate into space or move deep into the Earth.

I'm not quite sure if the question is asking about glacial, ice ages, or snowball Earth, and whether it's about the onset or end of a glacial period. I'll try to hit all three.
Ice Ages and Milankovitch Cycles
Ice ages are long spans of time that marked by periods of time during which ice reaches far from the poles, interspersed by periods during which the ice retreats (but never quite goes away). The periods of time during which ice covers a good sized fraction of the Earth are called glacials; the periods during which ice retreats to only cover areas in the far north and far south are called interglacials. We are living in ice age conditions, right now. There's still ice on Antarctica and Greenland. We are also in an interglacial period within that larger ice age. The current ice age began about 33 million years ago while the current interglacial began about 11,700 years ago.
The Milankovitch cycles determine whether the Earth is in a glacial or interglacial period. Conditions are right for ice to form and spread when precession puts northern hemisphere summer near aphelion and winter near perihelion and when both obliquity and eccentricity are low. The Earth currently satisfies the first of those conditions, but obliquity and eccentricity are a bit too high. That makes our northern hemisphere summers are a bit too warm, our winters a bit too cold.
The Milankovitch cycles] provides several answers to the question "where does the energy go?" Those times when conditions are ripe for glaciation have energy in the northern hemisphere spread more uniformly across the year than times not conducive to glaciation. Summers are milder, which means accumulated snow doesn't melt as much. Winters are milder, which means more snow falls.
Once ice does become ubiquitous, another answer to the "where does the energy go" question is into space. Ice and snow are white. Their presence reduces the amount of sunlight absorbed by the Earth.
The first paper listed below by Hays et al. is the seminal paper that brought the concept of Milankovitch cycles to the forefront. The second paper by Abe-Ouchi et al. dicusses a recent climate simulation that successfully recovers many salient features of the most recent glaciations. Most importantly, this paper appears to have solved the 100,000 year mystery and shows why deglaciation operates so quickly.

Hays, J. D., Imbrie, J., & Shackleton, N. J. (1976, December). "Variations in the Earth's orbit: Pacemaker of the ice ages." American Association for the Advancement of Science.
Abe-Ouchi, A., Saito, F., Kawamura, K., Raymo, M. E., Okuno, J. I., Takahashi, K., & Blatter, H. (2013). "Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume." Nature, 500(7461), 190-193.
Icehouse Earth vs Greenhouse Earth
The Earth's climate appears to have been toggling between two climate extremes for much of the Earth's existence, one where things are cold and ice is likely to form and the other where ice is absent worldwide except maybe right at the poles. Dinosaurs roamed the arctic and Antarctica when the Earth was in one of its greenhouse phases. The Earth has been in a greenhouse phase for most of the Earth's existence.
Milankovitch cycles don't cause glaciation during greenhouse Earth periods. Ice ages happen when the Earth is in an icehouse phase. What appears to distinguish greenhouse and icehouse phases are the positions and orientations of the continents. Having a continent located over a pole helps cool the climate. Having continents oriented so they channel ocean circulation in a way that keeps the ocean cool also helps cool the climate.
The Earth transitioned from its hothouse mode to its icehouse mode 33 million years ago or so. That's right about when two key events happened in the ocean. Up until then, Antarctica was still connected to both Australia and South America. The separation from Tasmania formed the Tasmanian Gateway, while the separation from South America formed the Drake Passage. This marked the birth of the very cold Southern Ocean, it marked the buildup of ice on Antarctica, and it marked the end of the Eocene.

Bijl, P. K., Bendle, J. A., Bohaty, S. M., Pross, J., Schouten, S., Tauxe, L., ... & Yamane, M. (2013). "Eocene cooling linked to early flow across the Tasmanian Gateway." Proceedings of the National Academy of Sciences, 110(24), 9645-9650.
Exon, N., Kennett, J., & Malone, M. Leg 189 Shipboard Scientific Party (2000). "The opening of the Tasmanian gateway drove global Cenozoic paleoclimatic and paleoceanographic changes: Results of Leg 189." JOIDES J, 26(2), 11-18.
Snowball Earth and the Faint Young Sun Paradox
Snowball Earth episodes were not your average ice age. Ice typically doesn't come near the tropics, even in the worst of ice ages. Snowball Earth means just that; the snow and ice encroached well into the tropics, possibly extending all the way to the equator.
The problem with snowball Earth isn't explaining where all the energy went. The real problem is explaining why the ancient Earth wasn't in a permanent snowball Earth condition, starting from shortly after the Earth radiated away the initial heat from the formation of the Earth.
The solar constant is not quite constant. While it doesn't change much at all from year to year, or even century to century, it changes a lot over the course of billions of years. Young G class stars produce considerably less energy than do middle aged G class stars, which in turn produce considerably less energy than do older G class stars. When our Sun was young, it produced only 75% or so as much energy than it does now.

Image source: http://en.wikipedia.org/wiki/File:Solar_evolution_(English).svg.
By all rights, the Earth should have been completely covered with ice. The young Sun did not produce enough energy to support open oceans. This obviously was not the case. There is plenty of geological evidence that the Earth had open oceans even when the Earth was quite young.
This 40 year old conundrum, first raised by Carl Sagan and George Mullen, is the faint young Sun paradox. There have been a number of proposed ways out of the paradox, but none of them quite line up with the geological evidence.
One obvious way out is that the Earth's early atmosphere was very different from our nitrogen-oxygen atmosphere and contained significantly more greenhouse gases. The amount of greenhouse gases needed to avert a permanent snowball Earth is highly debated, ranging from not much at all to extreme amounts. Another way out is a reduced albedo due to the significantly smaller early continents and lack of life. The young Earth would have been mostly ocean, and ocean water is rather dark (unless it's covered with ice). Lack of life means no biogenic cloud condensation nuclei, which means fewer clouds.

Goldblatt, C., & Zahnle, K. J. (2011). "Faint young Sun paradox remains." Nature, 474(7349), E1-E1.
Kienert, H., Feulner, G., & Petoukhov, V. (2012). "Faint young Sun problem more severe due to ice‐albedo feedback and higher rotation rate of the early Earth." Geophysical Research Letters, 39(23).
Rosing, M. T., Bird, D. K., Sleep, N. H., & Bjerrum, C. J. (2010). "No climate paradox under the faint early Sun." Nature, 464(7289), 744-747.

,
          I propose that the “snow ball Earth” was brought to a close by the dust from a huge meteorite (the largest known on Earth) impacting Australia (see http://charles_w.tripod.com/antipode.html ) settling onto the ice and melting it by a bare soil warming affect (see http://charles_w.tripod.com/climate.html ) and thus initiating the Cambrian. The dust fertilizing the ocean probably contributed considerably to the explosion of life then. That initiation was probably considerably assisted by the subsequent release of methane gas from methane ice under the ocean floor and by dust from volcanic eruptions from the Bahamas Islands, which are located at the antipode (opposite side of a sphere) of the above impact. The close correlation of volcanoes on Mars with meteorite impacts at their antipodes gives supporting evidence for such a phenomenon.

.
                    Sincerely,  Charles Weber


How important is understanding linear algebra in groundwater modeling? I am considering taking a course in linear algebra and wanted to get a survey to see how important it is. My goal is not just to understand how to push the buttons in some software (e.g. GW Vistas, Aquiferwin32), but to really understand how groundwater modeling works.

Relatively important, depending on the basic principles of the modeling you are interested in, and to what extent you want to get yourself involved in it.

In many areas of computational geophysics, e.g. atmospheric, oceanic, hydrological modeling etc., there are modelers, modelers, and modelers. First group of modelers get model output from somebody else, do some analysis, make some plots, and write about what they found. Then, there are modelers who design their own experiments, play with tunable parameters, maybe even change a few lines in the code and run the model. Finally, there are modelers - these spend most of their time on building and improving models, both in terms of numerical methods and software design. They could go for few years without publishing a single paper, but boy did they work hard.

If you are interested in computational science aspects of modeling, i.e. the inner workings of the model and how to improve it, understanding linear algebra as well as numerical methods will prove to be very valuable. While it is likely that you will never end up having to implement that matrix inversion or sparse matrix multiply yourself, and instead use one of many well documented production libraries, it is important to understand how they do it and why they do it in a particular way. From my own experience, I can say that most of the time it won't matter, but sooner or later there comes a situation where having knowledge about how low-level operations work will save you from pulling your hair out for weeks.

And this does not go only for linear algebra - I would extend this advice and urge you to strive at also understanding differential equations, discretization, computer architecture, floating-point arithmetic.

These days, not so much.

Even people who write their own sophisticated mesh based groundwater modeling codes usually make extensive use of sparse/dense numerical libraries/solvers that are written by linear algebra experts (e.g., UMFPACK/MUMPS/PETSc etc.). The author of these libraries really know their stuff.

So if you are writing your own groundwater modeling code you simply call the above libraries to solve your equations.

Off course 20 years ago when there were no such libraries people had no choice. That is why codes written in 80s and early 90s typically have their own (often poor performing) solver.

Edit: If you're just using a code then don't bother with linear algebra at all. The only thing you need to know is that for large problems you need to use an 'iterative' solver.


Has Earth's atmosphere lost mass throughout the geological ages due to biological $\small\sf{CO_2}$ fixation? Stromatolites and other organisms have been storing $\small\sf{CO_2}$ in the form of $\small\sf{CaCO_3}$ throughout the geological ages, forming extensive limestone deposits scattered across Earth's crust.

Has this $\small\sf{CO_2}$ fixation process reduced significantly atmosphere mass?

Or, as part of a biological cycle, it hasn't changed the quantity of molecules of Earth's atmosphere and has only changed atmosphere composition?

Yes, the Earth's atmosphere has thinned in the past few billion years, and biological fixation of CO2 was one of the main causes. It also gave us our present abundance of oxygen (21%). Enormous quantities of CO2 were used in the form of CaCO3 by foraminifera, corals etc to make their hard skeletons, and the resulting sediments formed limestone. Other elements formed compounds with carbonic acid (CO2 + H2O) to create other carbonate rocks.

In addition there is the more obvious sequestration of CO2 which was taken from the atmosphere by photosynthetic organisms and buried underground in the form of fossil hydrocarbons (oil, coal, gas, lignite etc). It was this which gave us our all-important oxygen. So the answer to your question is that biological activity has done both. It has hugely reduced the mass of the Earth's atmosphere, and at the same time greatly altered its composition.

It is also worth noting that the Earth loses substantial quantities of atmospheric gases into space, mostly hydrogen, but other gases as well. The bombardment of the outer atmosphere by ultraviolet rays, cosmic rays and the solar wind plays a part in this.


How to reduce the atmospheric temperature artificially? Is there any gas/substance which absorbs/reduces atmospheric temperature?

Ozone filters UV rays from the sun light and allows in infrared rays. In my knowledge these infrared rays are the cause of the heat. Do we have any provision to block these infrared rays at least for a targeted area? Does any gas or any other substance, natural or human-made, work in this way?

Ozone does not "filter" UV, it absorbs UV radiation (and undergoes some photo-chemistry reactions in the process).  By absorbing those wavelengths it prevents them from reaching us at the surface, but cause a temperature rise in the stratosphere.

We have plenty of gasses that behave this way for terrestrial radiation (however without the photo-chemical reactions).  Some of these gases are $\mathrm{CH_4}$, $\mathrm{CO_2}$ and $\mathrm{H_2 O}$, which we term greenhouse gases for their ability to readily absorb and radiate at terrestrial (infrared) wavelengths.  If concentrations are high enough, they would reduce some of the infrared spectrum from the sun reaching the surface, but they would also reduce terrestrial emissions into space.  Wherever these gases are doing the absorption one would also experience warming.

If you really want to reduce the global temperature solely through radiative forcing, the answer isn't to find and use a gas to absorb infrared radiation.  The answer is to reduce the concentrations of greenhouse gases in the region you are concerned with.  This will not greatly effect the incoming solar radiation, but it will allow greater radiative losses from the earth and atmosphere (lost to space), resulting in cooling.

You mention that "In my knowledge these infrared rays are the cause the heat".  While infrared radiation will make you hot (e.g. when the sun shines on your skin), the peak emission from the sun is in the visible spectrum and the primary energy source is in wavelengths shorter than infrared.  This shortwave radiation heats the surface of the Earth which in turn conducts heat to the atmosphere and radiates in the infrared.  Without the presence of greenhouse gases, our planet as is (current albedo, etc) would have a global mean temperature around 255 K, which is quite a bit colder than what we experience with greenhouse gases.  If you want to reduce temperatures, regionally or globally with a gas, your answer is to remove some of them, not add to them.

Add a heat sink. A heat sink is an absorber of heat. So add co2, or dry ice as we usually call it. It is an excellent heat sink.


Are atmospheric halogen oxides "supposed to be" in the atmosphere? Where do they come from? I like to naively think of Earth's natural atmosphere as nitrogen, oxygen, argon, water, carbon dioxide and okay, some nitrogen and sulfur oxides, and again okay, a little hydrogen and methane from microorganisms. Everything else is pollution and shouldn't be there.

Just because I like to naively think that way doesn't meant it's so.

The excellent answers to Why are atmospheric BrO and ClO important to measure by satellite? talk about halogen oxides.

Are they a natural component of Earth's atmosphere, purely pollution, or a mixed bag?

Classifying the presence of halogen oxides in the atmosphere as either natural, pollution or mixed bag, would result in mixed bag.

Natural sources of halogen oxides include the ocean and volcanoes. In 1963, Duce et al,

  showed that bromine, like chlorine, was lost from the sea salt particles

Volcanoes are another source of halogen oxides,

  Halogens are emitted from volcanoes primarily as hydrogen halides (HCl, HF, HBr, and HI). Upon mixing with the atmosphere, chlorine and bromine species are partially converted to the halogen oxides OClO and BrO.

and

  Traditionally, emissions of volcanoes were regarded to be mainly of importance for the atmospheric sulfur cycle, acid deposition, and stratospheric effects from explosive eruptions. This view changed recently, mainly because of the observation of very high concentrations of bromine oxide, BrO, in the tropospheric, nonexplosive plume of Soufrière Hills, Montserrat.

The Sun is a requirement for the ocean source of halogen oxides.

Salt lakes, such as the Great Salt Lake in Utah are also sources of halogen oxides.

Forest fires can be a source of fluorine.

Pollution sources of halogen oxides includes: steel production, phosphate fertilizer production, burning coal, the manufacture of glass and ceramics.

Bromine and chlorine are used in cleaning products which are another source. Fire fighting chemicals such as PFAS (PolyFluoroAlkyl Substances) are another source.

Bromine and chlorine are very reactive, so are always found as compounds. They are fairly common elements, mainly in the oceans but also in the Earth's crust. Both have industrial uses, and both damage the Earth's ozone layer. They are evaporated from the ocean by strong sunlight in the form of oxides (BrO and ClO), and in trace amounts are natural constituents of the atmosphere. Very small amounts of these atmospheric halogens are anthropogenic.

As strong sunlight is the motive force for evaporating these halogens from the sea (and also from salt evaporite deposits on land), most of the troublesome halogens come from tropical or subtropical seas, and a lesser amount from temperate seas. Measures have already been taken to reduce the anthropogenic component, but there seems to be nothing we can do about naturally produced halogen oxides.

As the Earth has managed quite well for billions of years despite this problem, which is responsible for the so-called ozone hole over Antarctica, which waxes and wanes, it doesn't seem like something we should worry about unduly, though of course our efforts to reduce the anthropogenic component should continue.


Why are mornings cooler than nights? In the morning, Google shows the temperature from four or five hours ago (around 2:00 a.m.). But then I update the report, and I get the temperature slightly lower than before.
Why is the temperature at 2:00 a.m. higher than the temperature at 7:00 a.m.?

The Earth is always radiating heat to the space. But in the day the Sun delivers some heat. The net heat flux is then defined as the sum of those two factors. If the energy delivered by the Sun is bigger than the cooling rate, the Earth is net warming (positive net flux – we can imagine it like heat is travelling "to us"), as opposed to the opposite case (cooling; negative net flux – heat is travelling "away").
In the day, the Sun warms the ground until the evening. The Sun's heating rate is higher than the cooling rate, so the temperature is rising until it gets to a point where the heating rate is same as cooling rate. This happens in the evening, so the temperature is steady at that point. But the Sun goes even lower, so the net flux becomes negative. In the night there is only cooling of Earth, so the temperature is falling steadily until the Sun is high enough that it balances the cooling. This happens at a point of a minimum temperature.
Of course, this is valid for most of the days, but we can have some other effects that can change the time of the minimum temperature (clouds, fronts or advection, for example).
On graph:

So, the temperature is falling over night after the sunset, but rises again after the sunrise. Thus, the temperature is at its lowest point in the morning.

Appendix for all you loving calculations:
Note: Simplified to toy model, no atmosphere
The cooling rate of the Earth is approximatelly given by the Stefan-Boltzmann equation:
$$j_E=\sigma\cdot T^4=5.670  \cdot 10^{-8} \frac{W}{m^2 K^4} \cdot (288.15 K)^4 = 390 \frac{W}{m^2}$$
The maximum heating rate of Sun in the zenith is $j_{\text{S max}}=1361 \frac{W}{m^2}$. So, the heating rate of Sun at altitude $\alpha$ is:
$$j_S=j_{\text{S max}}\cdot \sin{\alpha}=1361 \frac{W}{m^2}\cdot \sin{\alpha}$$
When is the heating rate equal to zero?
$$0=j_S-j_E=1361 \frac{W}{m^2}\cdot \sin{\alpha} - 390 \frac{W}{m^2}$$
$$1361 \frac{W}{m^2}\cdot \sin{\alpha} = 390 \frac{W}{m^2}$$
$$\alpha = 17 °$$
So, with our calculations, the minimum temperature is at the time when the altitude is equal to 17°.

Your question is a bit ill-formed. There are more precise statements that we might take you as asking, for instance you might be claiming that the low takes place after sunrise, and be asking why that is. A very basic model of the temperature is that it is a sinusoidal function of time, and it is driven by the intensity of solar energy, also modelled as a sinusoidal function of time (that is, the net power, when the heat radiating from the Earth is subtracted from the heat coming from the Sun, is modelled as a sin function). If we had that the solar power is $P(t) = -\cos(t)$ where midnight is considered to be both $0$ and $2\pi$, and temperature is $T(t)$ where $T'(t) = P(t)$, then we would actually have $T$ and $P$ being $\pi/2$ (that is, six hours) out of phase with each other. That is, solving for $T(t)$ gives us $\sin$, and $\sin(t)$ is the same as $P(t-\pi/2)$.
The actual equation will be much more complicated: solar power isn't a sine wave, there are heat reservoir effects, radiative cooling depends on the current temperature, etc. The actual displacement between the minima will depend on all of those factors, but the general principle that the forcing function and the response function tend to be out of phase holds.


What is the loudest thunder ever recorded (dB) at ground level and where did it occur? Sound travels fastest through warm air and conditions such as temperature inversions can help to amplify the sound of thunder (source).  Conversely, during a thundersnow event the falling, and accumulated, snow can act as an acoustic suppressor (source). Originally I was thinking that the loudest thunder at ground levels would simply be at higher elevations, however the atmospheric conditions mentioned above, and others that I'm not aware of, have me wondering where the loudest thunder would actually occur.

Thunder 1 mile away-117 dB
Thunder 1/2 mile away-121 dB
Lightning strike just meters away from you-125 dB


What factors influence cloud height and type? For example, why do altocumulus clouds fail to form at 6400m in high latitude locations, but will form at this height at a lower latitude? Is it simply an issue of temperature?

It depends on the height of the troposphere. On the equator troposphere has at least 12 km height, but in the polar latitudes it might be even less than 8 km. That difference in troposphere altitude allows clouds to form differently depending on the latitude. The second reason is that higher parts of the troposphere closer to the equator are warmer and contain more moisture than in the polar region.