Global warming on our planet has become, it seems, a well-known fact. And experts warn that this global warming, which occurs due to the greenhouse effect in the atmosphere, could have the most serious consequences. Therefore, it is planned to conduct research into the effects of the greenhouse effect not only on Earth, but also on Venus, Mars and Titan (satellite of Saturn), so that humanity can more clearly imagine what climate vicissitudes can await it in the future.

While humanity was small in number and not burdened with technical achievements, its activities had little influence on the Earth’s climate. But now people are actively interfering with the process of heat exchange on our planet, often without thinking about the consequences.

Energy from the Sun heats the surface of the Earth, which in turn radiates this energy back into space. But some atmospheric gases prevent this energy from leaving the atmosphere. This is the greenhouse effect. Without it, the average temperature on Earth, which is now 15 o C, would be 30 o lower. By burning fuel and cutting down forests, humans emit a lot of greenhouse gases into the atmosphere, thereby increasing the greenhouse effect. As a result, over the last century, global temperatures on Earth have increased by more than half a degree.

An example of what can happen when the greenhouse effect becomes too strong can be seen on Venus. This planet is only slightly inferior in size and mass to Earth. But the temperature on its surface is about 460 o C. Now the atmosphere of Venus consists almost entirely of carbon dioxide, which is a greenhouse gas. In the earth's atmosphere, the share of carbon dioxide is still about 0.03%. This seems to be very little, but since the beginning of industrial development, the share of carbon dioxide in the atmosphere has increased by 30%.

Why is the composition of the atmosphere on Venus so different from that on Earth? Perhaps the fate of Venus also awaits the Earth? This question may be answered by the European probe Venus Express, which will set off to explore Venus in 2005.

Our other neighboring planet, Mars, is not at all like Venus. There are no signs of a greenhouse effect yet on Mars. There is carbon dioxide in its atmosphere, but the atmosphere itself is so thin and rarefied that its pressure on the surface is only a hundredth of the “earthly” 760 mm Hg. Art. Therefore, it does not retain any energy from the Sun, and there are sharp temperature contrasts between day and night, as well as light and shadow. Many experts believe that in the past Mars was much warmer, and that there were even oceans there, and therefore the atmosphere was completely different. However, about 3.6 billion years ago something happened on Mars, and over time it came to its current state. What could be the impetus for such climate change? Scientists plan to answer this question with the help of the European probe Mars Express, which will go to Mars in May this year.

There is a greenhouse effect of intermediate intensity on Saturn’s largest moon, Titan. True, in its atmosphere it is explained by high concentrations of methane, which is also a greenhouse gas. But on Titan it is still much colder than on Earth - about -180 o C. Now the Cassini probe with the Huygens miniprobe is flying towards Saturn. The latter is intended specifically for Titan research. To do this, it will be dropped into the atmosphere by parachute. Perhaps these studies will allow earthlings to learn something useful for understanding the processes on their planet.

With a CO2 pressure of over 90 bar at the surface and a temperature of 733 Kelvin, rather than the effective temperature for Venus of about 240 K (Pollack 1979). Unlike Venus, the greenhouse effect is currently around 33 K overheating, which also plays an important role in supporting life. The greenhouse effect is small at 5 K, although research suggests it was significantly larger in the past (Carr and Head, 2010). Interestingly, the greenhouse effect has much in common with that on Earth, including comparable surface pressure there (1.5 times that of Earth, unlike Venus and Mars, which have pressures about 100 times greater, and 100 times less, respectively), and also condensable greenhouse gases are present on Titan, despite the low temperatures (Koustenis, 2005).

Comparative planetology can be used to look at these planets collectively and outline the underlying laws and significance of the greenhouse effect. Such a comparative analysis can provide insight into possible atmospheric envelopes and conditions on Earth-like surfaces. This work looks at more than just four sets of data about the current state, because it can also rely on the possible atmospheric conditions that existed on them in the past, taking into account geological, geochemical and isotopic evidence and other fundamental physical reasons.

The structure of this work is as follows: first, we consider the physical basis of the greenhouse effect and gases that absorb radiation. Second, let's briefly look at each of the four cosmic bodies listed above, the main absorber gases, the structure of the atmosphere, and the prevailing surface conditions of the various bodies. We will also consider possible patterns of past conditions, taking into account how they relate to data on various atmospheric conditions in the past and the paradox of the weak young. And finally, let’s tie all these threads together and find out the basic physical processes associated with each planet and draw analogies between them. Please note that this article focuses primarily on quality characteristics.

GREENHOUSE GASES BASICS

Greenhouse gases transmit visible light, allowing most sunlight to escape the atmosphere and reach the surface, but they are opaque in the infrared, affecting radiation in such a way that the surface temperature increases and the planet is in thermal equilibrium with the incoming solar radiation.

The physical process by which atoms and molecules absorb radiation is complex, and involves many laws of quantum mechanics to describe the full picture. However, it is possible to qualitatively describe the process. Each atom or molecule has a set of states corresponding to different quantized energy levels. A molecule can go from a lower energy state to a higher energy state either by absorbing a photon or from a high energy collision with another particle (it is worth noting that it is not a fact that all possible higher energy states can be reached directly from a given lower one and vice versa ). After entering an excited state, a molecule can be excited to a lower energy state or even to the ground state (lowest energy state) by emitting a photon or transferring some of its energy to another particle after colliding with it. There are three types of transitions for absorber gases in the Earth's atmosphere. In order of decreasing energy, they are: electronic transitions, vibrational transitions and rotational transitions. Electronic transitions occur with energies in the ultraviolet range, vibrational and rotational transitions occur in the near and mid-infrared region of the spectrum. Ozone is an example of oxygen absorbing ultraviolet rays, while water vapor has noticeable vibrational and rotational energies in the infrared. Because infrared radiation dominates the Earth's radiation, rotational and vibrational transitions are most important when discussing the Earth's thermal balance.

This is not the whole story, because each absorption line depends on particle speed (temperature) and pressure. Changing these quantities can cause changes in the spectral lines and thus change the absorption of radiation provided by the gas. In addition, another mode of absorption related to very dense or very cold atmospheres, collision-induced absorption (known as COI), remains to be discussed. Its meaning is that ICP allows non-polar molecules (i.e., symmetrical molecules without a strong dipole moment) to absorb radiation. This works in one of two ways: first, the collision causes a temporary dipole moment on the molecule, allowing the photon to be absorbed, or second, two molecules, such as H2-N2, briefly bond into one supermolecule with their own quantized rotational states. These transient molecules are called dimers (Hunt et al. 1983; Wordsworth et al. 2010). The direct proportionality of density is quite easy to understand intuitively: the denser the gas, the greater the likelihood of a collision. The negative relationship with temperature can be understood as an effect of residence time - if a molecule has a lot of translational energy, it will spend less time in close proximity to another molecule, thus dimer formation is less likely.

Knowing the numerical values ​​of the radiation forcing characteristics, temperatures can be easily calculated in the absence of any feedback effects. If the surface temperature is adjusted, more energy will be emitted into space (Hansen, Sato and Rudy 1997). In general, understanding climate feedback is critical, since negative feedback stabilizes temperature, while positive feedback increases disturbances and creates runaway processes. The significantly different timing of feedback effects is also very important. It is often necessary to refer to a general circulation model (GCM) incorporating all important feedback effects at appropriate time scales to make accurate predictions (Taylor 2010). Examples of feedback effects are: temperature-dependent cloud formation (negative feedback, short time scales), melting or formation of significant ice cover (positive feedback, short/medium time scales), carbonate-silicate cycle (negative feedback, long time frames) and biological processes (various).

GREENHOUSE EFFECT IN THE SOLAR SYSTEM

Earth

The average annual surface temperature of the Earth is 288 K and the effective temperature is 255 K. The effective temperature is determined by the ratio of the heat balance to the incoming solar radiation flux according to the equation below

where S is the solar constant (on earth ~ 1366 W / m2), A is the geometric albedo of the Earth, σ is the Stefan-Boltzmann constant, f is the geometric factor, equal to 4 for rapidly rotating planets, i.e. planets with rotation periods on the order of days (Catling and Kasting 2013). Therefore, the greenhouse effect is responsible for the increase in this temperature on Earth by 33 K (Pollack 1979). The entire Earth should radiate as a black body, heated to 255 K, but absorption by greenhouse gases, primarily CO2 and H2O, returns heat back to the surface, creating a cold upper atmosphere. These layers radiate at temperatures well below 255 K and therefore, in order to radiate like a black body at 255 K, the surface must be warmer and radiate more. Most of the flow leaves through the 8-12 micron window (a wavelength region relatively transparent to the atmosphere).

It is important to emphasize that the cold upper atmosphere is positively correlated with a warm surface - the more the upper atmosphere is able to radiate, the lower the flux that must come from the surface (Kasting 1984). Therefore, it should be expected that the greater the difference between the temperature minimums of the surface and the upper layers of the planet’s atmosphere, the greater the greenhouse effect. Hansen, Sato and Rudy (1997) showed that a doubling of CO2 concentration is equivalent to a 2% increase in solar radiation flux, ignoring feedback effects.

The main greenhouse gases on Earth are water vapor and carbon dioxide. Much lower concentration gases such as ozone, methane and nitrogen oxides also contribute (De Pater and Lisauer 2007). Notably, while steam is the largest contributor to greenhouse heating, it condenses and “synchronizes” with non-condensable greenhouse gases, most notably CO2 (De Pater and Lisauer, 2007). Water vapor can release latent heat to the atmosphere by condensing, shifting the temperature gradient in the troposphere to moist adiabatic rather than dry. Water cannot enter the stratosphere and undergo photolysis due to the tropospheric cold trap, which condenses water vapor at a temperature minimum (at the tropopause).

Evolution of the atmosphere

The presence of sedimentary rocks and the apparent absence of glacial deposits on the Earth around 4 billion years ago suggests that the early Earth was warm, perhaps warmer than today (De Pater and Lisauer 2007). This is especially problematic since solar radiation flux is believed to have been around 25% lower at the time. This problem is known as the “Weak Young Sun Paradox” (Goldblatt and Zahnle 2011). A possible explanation could be a much larger greenhouse effect than today. Concentrations of CH4, CO2 and H2O and possibly NH3 are believed to have been greater at that time (De Pater). Many hypotheses have been put forward to explain this discrepancy, including much greater partial pressure of CO2, a significant greenhouse effect due to methane (Pavlov, Kasting, and Brown, 2000), an organic fog layer, increased cloudiness, broadening of spectral lines due to pressure from -due to significantly higher partial pressures of nitrogen and total atmospheric pressure (Goldblatt et al. 2009).

Venus

While Venus is often described as Earth's sister due to its similar mass and size, its surface and atmospheric conditions have nothing in common with Earth. The surface temperature and pressure are 733 K and 95 bar, respectively (De Pater and Lisauer 2007, Krasnopolsky 2011). Thanks to the high albedo and 100% cloudiness, the equilibrium temperature is about 232 K. Therefore, the greenhouse effect on Venus is simply monstrous and equal to about 500 K. This is not surprising with a partial pressure of CO2 of 92 bar. Line broadening by pressure is significant at these densities and contributes significantly to warming. CO2-CO2 ICP may also contribute, but there is no literature yet on this. Water vapor content is limited to 0.00003% by volume (Meadows and Crisp 1996).

Evolution of the atmosphere

It is often believed that Venus began with a volatile set similar to that of Earth and a similar initial isotopic composition. If this is true, then the measured Deuterium/Protium ratio of more than 150 for Earth (Donahue et al. 1982) indicates large losses of hydrogen in the past, presumably due to photodissociation of water (Chassefier et al. 2011), although Grinspoon Lewis (1988) suggested that water delivery could explain this isotopic signature. In any case, Venus could have had oceans before its current state if it had contained as much water as Earth does (Kasting 1987). Her condition could not have been caused by increased concentrations of CO2 (or any other greenhouse gas) alone, but is generally thought to be caused by increased influx of solar energy (Kippenhahn 1994), although the internal heat flow causing the runaway greenhouse effect on tidally locked planets is also possible (Barnes et al. 2012).

Kasting (1987) examined both runaway and persistent greenhouse effects on Venus. If Venus had an ocean early in its history, the solar energy flux in its current orbit would be such that a greenhouse scenario would begin almost immediately. There are two scenarios for ocean water loss due to increased solar radiation flux (Kasting 1987, Goldblatt et al. 2011, Catling and Kasting 2013). The first uncontrolled scenario: the ocean begins to evaporate into the troposphere, increasing the heating, but the pressure also increases, so the oceans do not boil. Water accumulates in the troposphere much faster than photodissociation and hydrogen escape into space. Weather events can still occur and slow down the release of CO2. The temperature and pressure of the water vapor increases and the ocean persists until the water reaches the critical point of 647 K, at which it is impossible to turn the vapor into water under any pressure, at which point all the still liquid water evaporates and creates a dense fog of water vapor, completely opaque to outgoing long-wave radiation. The surface temperature then increases until it begins to radiate in the near-infrared and visible regions, where the transparency of water vapor is much higher and more stable. This corresponds to a temperature of 1400 K, high enough to melt near-surface rocks and release carbon from them. In addition, without weathering, CO2 can be released from the rock and not removed anywhere. In the second scenario, the release of water vapor into the atmosphere makes the temperature distribution more isothermal, raising the tropopause and destroying the cold trap. Water vapor can therefore move into the stratosphere and undergo photolysis. Unlike the first scenario, water is lost at a rate commensurate with the rate of evaporation from the ocean, and evaporation will not stop until all the water is gone. When the water runs out, the carbonate-silicate cycle turns off. If CO2 continues to be released from the mantle, there is no available way to remove it.

Mars is in some ways the opposite of Venus in terms of temperature and pressure. The surface pressure is approximately 6 millibars and the average temperature is 215 K (Carr and Head 2010). The equilibrium temperature can be shown to be 210 K, so the greenhouse effect is about 5 K and is negligible. Temperatures can vary between 180 K and 300 K depending on latitude, time of year and time of day (Carr and Head 2010). Theoretically, there are short periods of time when liquid water could exist on the Martian surface according to the phase diagram for H2O. In general, if we want to see a wet Mars, we must look to the past.

Evolution of the atmosphere

Mariner 9 sent back photographs for the first time showing obvious traces of river flows. The most common interpretation is that early Mars was warm and wet (Pollack 1979, Carr and Head 2010). Some mechanism, presumably the greenhouse effect (though clouds have also been considered), which must have been caused by sufficient radiative forcing, made Mars warmer during its early history. The problem is even worse than it first appears, given that the Sun was 25% dimmer 3.8 billion years ago, when Mars had a mild climate (Kasting 1991). Early Mars may have had surface pressures on the order of 1 bar and temperatures close to 300 K (De Pater and Lisauer 2007).

Kasting (1984, 1991) showed that CO2 alone could not have warmed the early surface of Mars to 273 K. Condensation of CO2 into clathrates changes the atmospheric temperature gradient and forces the upper atmosphere to radiate more heat, and if the planet is in radiative equilibrium, then the surface emits less so that the planet has the same outgoing flux of long-wave infrared radiation, and the surface begins to cool. Thus, at pressures above 5 bar, CO2 cools the planet rather than warms it. And this is not enough to heat the Martian surface above the freezing point of water, given the solar flux at that time. In this case, CO2 will condense into clathrates. Wordsworth, Foget, and Amit (2010) presented a more rigorous treatment of the physics of CO2 absorption in a dense, clean CO2 atmosphere (including ICP), showing that Kasting in 1984 actually overestimated surface temperatures at high pressures, thereby exacerbating the problem of warm, wet early Mars. Other greenhouse gases in addition to CO2 could solve this problem, or perhaps dust if it reduced the albedo.

The possible role of CH4, NH3 and H2S has been previously discussed (Sagan and Mullen, 1972). Later, SO2 was also proposed as a greenhouse gas (Jung et al., 1997).

Titan's surface temperature and pressure are 93 K and 1.46 bar, respectively (Koustenis). The atmosphere consists mainly of N2 with a few percent CH4 and about 0.3% H2 (McKay, 1991). Titan's tropopause with a temperature of 71 K at an altitude of 40 km.

Titan's greenhouse effect is primarily caused by pressure-induced absorption of long-wave radiation by N2, CH4 and H2 molecules (McKay, Pollack and Cortin 1991). H2 strongly absorbs the radiation typical of Titan (16.7-25 microns). CH4 is similar to water vapor on Earth, as it condenses in Titan's atmosphere. The greenhouse effect on Titan is mainly due to collision-induced absorption by N2-N2, CH4-N2 and H2-N2 dimers (Hunt et al. 1983; Wordsworth et al. 2010). This is strikingly different from the atmosphere of Earth, Mars and Venus, where absorption through vibrational and rotational transitions predominates.

Titanium also has a significant anti-greenhouse effect (McKay et al., 1991). The anti-greenhouse effect is caused by the presence at high altitudes of a layer of haze that absorbs visible light, but is transparent to infrared radiation. The anti-greenhouse effect reduces surface temperature by 9 K, while the greenhouse effect increases it by 21 K. Thus, the net greenhouse effect is 12 K (82 K effective temperature compared to 94 K observed surface temperature). Titan without the haze layer will be 20 K warmer due to the lack of anti-greenhouse effect and the enhanced greenhouse effect (McKay et al. 1991).

Surface cooling is mainly due to radiation in the 17-25 micron region of the spectrum. This is Titan's infrared window. H2 is important because it absorbs in this region, just as CO2 is very important on Earth because it absorbs infrared radiation from the Earth's surface. Both gases are also not constrained by the saturation of their vapors in the conditions of their atmosphere.

Methane is close to its vapor pressure, similar to H2O on Earth.

Evolution of the atmosphere

Due to increased solar luminosity, Titan's surface temperature is likely 20 K warmer than it was 4 billion years ago (McKay et al. 1993). In this case, the N2 in the atmosphere would be cooled to ice. The formation and lifetime of Titan's atmosphere is an interesting problem without any solid solutions (Koustenis 2004). One problem is that at this rate of CH4 photolysis and ethane production, the current supply of CH4 in Titan's atmosphere would be depleted in much less time than the age of the solar system. In addition, liquid ethane would accumulate on the surface several hundred meters below at today's production rates (Lunine et al., 1989). Either this is an uncharacteristic period in Titan's history, or there are unknown sources of methane and sinks for ethane (Catling and Kasting, 2013).

CONCLUSIONS AND DISCUSSION

Earth, Mars, and Venus are similar in that each planet has a noticeable atmosphere, weather, past or current volcanism, and a chemically heterogeneous composition. Titan also has a significant atmosphere, weather, possibly cryovolcanism, and potentially partially heterogeneous composition (De Pater and Lisauer 2007).

Mars, Earth and Venus have a greenhouse effect with a noticeable influence of CO2, although the magnitude of the warming and partial pressure of CO2 differs by several orders of magnitude. It is quite obvious that the Earth and Mars must have had additional heating earlier in the history of the solar system, when the Sun shone weaker. It is unclear what the source(s) of warming were for these two planets, although many solutions have been proposed and many explanations are possible. Interestingly, Mars allows for comparisons with Earth's past, since both planets have plenty of geological evidence that they were warmer, having more than the greenhouse effect created by CO2 gas. At the same time, the runaway greenhouse effect on Venus provides insight into the future of Earth if solar activity continues to increase. By comparing models for all three planets, knowing the fundamental physical laws that are the same for all planets, we can obtain things that would be impossible to obtain if the Sun did not influence the terrestrial planets.

Titan is an exciting material for study, according to the author, especially since, unlike other described worlds, its greenhouse effect is dominated by collision-induced absorption. Heating due to ICP has many possible applications to describe the conditions and possible habitability of exoplanets (Pierrehumbert). Like Earth's atmosphere, Titan's atmosphere contains enough material close to the triple point that can condense in the atmosphere and is therefore capable of influencing temperature distribution.

The main types of gases in the Earth's atmosphere are, of course, influenced by living organisms (Taylor 2010). Obviously, this is not true for other planets in the solar system. However, we can use comparisons between Earth and lifeless worlds in our system to better understand possible other biospheres.

The greenhouse effect is an increase in the temperature of the lower layers of the planet's atmosphere compared to the effective temperature, that is, the temperature of the planet's thermal radiation observed from space.

Gardeners are very familiar with this physical phenomenon. The inside of the greenhouse is always warmer than the outside, and this helps to grow plants, especially in the cold season. You may feel a similar effect when you are in a car. The reason for this is that the Sun, with a surface temperature of about 5000°C, emits mainly visible light - the part of the electromagnetic spectrum to which our eyes are sensitive. Because the atmosphere is largely transparent to visible light, solar radiation easily penetrates the Earth's surface. Glass is also transparent to visible light, so the sun's rays pass through the greenhouse and their energy is absorbed by the plants and all objects inside. Further, according to the Stefan-Boltzmann law, every object emits energy in some part of the electromagnetic spectrum. Objects with a temperature of about 15°C - the average temperature at the Earth's surface - emit energy in the infrared range. Thus, objects in a greenhouse emit infrared radiation. However, infrared radiation cannot easily pass through glass, so the temperature inside the greenhouse rises.

A planet with a stable atmosphere, such as Earth, experiences much the same effect -- on a global scale. To maintain a constant temperature, the Earth itself needs to emit as much energy as it absorbs from the visible light emitted towards us by the Sun. The atmosphere serves as glass in a greenhouse - it is not as transparent to infrared radiation as it is to sunlight. Molecules of various substances in the atmosphere (the most important of them are carbon dioxide and water) absorb infrared radiation, acting as greenhouse gases. Thus, infrared photons emitted by the earth's surface do not always go directly into space. Some of them are absorbed by greenhouse gas molecules in the atmosphere. When these molecules re-radiate the energy they have absorbed, they can radiate it both outward into space and inward, back toward the Earth's surface. The presence of such gases in the atmosphere creates the effect of covering the Earth with a blanket. They cannot stop heat from escaping outward, but they allow heat to remain near the surface for a longer time, so the Earth's surface is much warmer than it would be in the absence of gases. Without the atmosphere, the average surface temperature would be -20°C, well below the freezing point of water.

It is important to understand that the greenhouse effect has always existed on Earth. Without the greenhouse effect caused by the presence of carbon dioxide in the atmosphere, the oceans would have frozen long ago and higher forms of life would not have appeared. Currently, the scientific debate about the greenhouse effect is on the issue of global warming: are we, humans, disturbing the energy balance of the planet too much as a result of burning fossil fuels and other economic activities, while adding excessive amounts of carbon dioxide to the atmosphere? Today, scientists agree that we are responsible for increasing the natural greenhouse effect by several degrees.

The greenhouse effect does not only occur on Earth. In fact, the strongest greenhouse effect we know of is on our neighboring planet, Venus. The atmosphere of Venus consists almost entirely of carbon dioxide, and as a result the surface of the planet is heated to 475 ° C. Climatologists believe that we have avoided such a fate thanks to the presence of oceans on Earth. The oceans absorb atmospheric carbon and it accumulates in rocks such as limestone - thereby removing carbon dioxide from the atmosphere. There are no oceans on Venus, and all the carbon dioxide that volcanoes emit into the atmosphere remains there. As a result, we observe an uncontrollable greenhouse effect on Venus.

The amount of water vapor in the atmosphere is directly related to the “greenhouse effect,” the essence of which is as follows. Although clouds reflect most of the sunlight back, some of it still passes through the atmosphere, hits the planet's surface and is absorbed by it. Since the planet is in thermal equilibrium (that is, not getting hotter over time), all the absorbed energy must be re-radiated into space. If the atmosphere did not interfere, the surface of the planet would cope with this task, heating up to about 230 K (averaged over the two hemispheres; of course, the daytime would be a little hotter, and the nighttime would be colder). In this case, the surface radiation would lie in the infrared range with a maximum between 10 and 15 μm. But it is precisely in this range that the atmosphere is less transparent. It intercepts a significant portion of the surface radiation and returns it back. This causes the surface to heat up even more, to a temperature at which the heat flow escaping into space still balances its influx from the Sun. Thus, equilibrium is restored, but with an increased surface temperature (735 K).

This effect is called “greenhouse”, since glass or film in a garden greenhouse plays the same role as the atmosphere of the planet: the roof of the greenhouse, transparent to light, transmits solar rays directed towards the ground, but blocks infrared radiation coming from the ground and rising currents of warm air.

Calculations show that the surface temperature of Venus exactly corresponds to the water vapor concentration of about 3?10 -5; if there were more of it, the opacity to infrared rays would increase significantly and the surface temperature would become even higher. Apparently, the initial temperature of Venus, due to its relative proximity to the Sun, was relatively high. This contributed to the release of water and carbon dioxide from the surface, which stimulated the greenhouse effect and a further increase in temperature.

Unlike other terrestrial planets, whose surfaces could be observed from Earth through a telescope, the surface of Venus cannot be seen even from orbit, since this planet is shrouded in a thick cloudy atmosphere. The temperature at its surface exceeds 460°C, the pressure is almost one hundred atmospheres, and most of all Venus resembles a desert. Lead melts on its surface, dense clouds of sulfur dioxide float across the sky, from which sulfuric acid rains from time to time and lightning strikes with a frequency 30 times higher than on Earth. The sun is never visible there due to a continuous layer of clouds and strong scattering of light by the dense atmosphere.

Estimated view of the surface of Venus in the area of ​​the Ishtar mountain range. On the horizon is Maat Peak (11 thousand m).

All this is the consequences of a catastrophic greenhouse effect, due to which the surface of Venus cannot cool effectively. The atmosphere's thick blanket of carbon dioxide traps heat coming from the Sun. As a result, such an amount of thermal energy accumulates that the temperature of the atmosphere is much higher than in the oven. On Earth, where the amount of carbon dioxide in the atmosphere is small, the natural greenhouse effect increases global temperatures by 30°C. And on Venus, the greenhouse effect raises the temperature by another 400°.

Venus is closer to the Sun and receives more thermal energy from it, however, if the atmospheric parameters of our planets were the same, then the average temperature on Venus would be only 60°C higher than on Earth. And in the region of the poles there would be a quite comfortable, from our point of view, temperature for living - about 20°C. But a small, at first glance, difference in temperature played a fatal role - at some point a positive feedback arose on Venus: the more the planet warmed up, the more the water there evaporated, the more water vapor, which is a greenhouse gas, accumulated in the atmosphere ... The temperature increased to such an extent that carbonate-containing rocks began to decompose there, and additional carbon dioxide entered the atmosphere - this created the very temperature of 500°C that we observe today.

Like modern Earth, Venus was once covered in oceans, but now contains water only in the atmosphere and in the thick clouds of sulfuric acid that envelop the planet - the once Venusian oceans boiled away due to the greenhouse effect. For the first two billion years, the planet's heating was controlled by intense cloud formation. Then the surface of Venus had a moderate temperature, and oceans of liquid water could well exist on it. High humidity and heat are the right combination for the emergence of life...

4.5 billion years ago, when the Earth first formed, it also had a very dense atmosphere of carbon dioxide - just like Venus. This gas, however, dissolves in water. Earth was not as hot as Venus because it is further from the Sun; As a result, the rains washed carbon dioxide out of the atmosphere and sent it into the oceans. Rocks such as chalk and limestone, which contain carbon and oxygen, arose from the shells and bones of sea animals. In addition, carbon dioxide was extracted from the atmosphere of our planet during the formation of coal and oil.

The Earth and Venus are very similar: in size, density, and the magnitude of the acceleration due to gravity. And the total amount of CO 2 on the planets is also approximately the same. Only on Venus has it already been released and is in the atmosphere, while on Earth most of it is still in a bound state, in the form of limestone, chalk, and marble. This is our main supply of CO 2.

Rocks on Earth can also begin to release carbon dioxide if they are heated properly. In the later stages of a greenhouse catastrophe, if we have one, they will make their contribution. But in the initial stages, other “natural storehouses” of carbon dioxide pose a much greater danger. Huge volumes of CO 2 are dissolved in the World Ocean. There is 60 times more carbon dioxide here than there is now in the atmosphere. And as the temperature rises, the solubility of CO 2 in the liquid decreases. This phenomenon is known to everyone as the “champagne effect”. If the champagne is cold, everything is fine. And if you heat it up...
So, if this law works, and most of the World Ocean manages to warm up to certain values, climate change will enter an irreversible stage - the more CO 2 is released, the more the temperature will rise. And its growth will contribute to the further release of carbon dioxide from the ocean.
There is another dangerous source of CO 2 - methane hydrates. This is a bound state of methane and water, methane ice. Today its deposits exist in a relatively stable state at low temperatures at great depths. With warming, these complexes become unstable and begin to decompose into methane and water. And methane is an even more active greenhouse gas than CO 2 . If the deep layers of the ocean begin to warm up, methane hydrates will be the most dangerous of all “useful” minerals.
Everything is like on Venus, like an avalanche. Only on Venus this most likely had a natural cause, unless, of course, we assume that there was once a civilization there that mined and burned Venusian coal and oil and ultimately did to its planet what we are doing now to the Earth.

PS The lifespan of research robots on the surface of Venus is calculated in minutes, so I had to make a landscape with lightning myself in Photoshop, based on a radar image (1) taken from Magellan orbit, and a color panorama in optical mode (2), which I managed to photograph and transmit “Venera-10” before dying in terrible agony.

P.P.S. If we stopped driving cars and closed factories right tomorrow, the amount of CO2 that is already in the atmosphere would give us a warming limit of about 10 degrees. Greenhouse gas has already been “pumped” into the atmosphere; it’s just that the thermal inertia of the World Ocean and glaciers is still playing its stabilizing role. They are a powerful buffer and delay the catastrophic rise in temperature for two hundred years. We've had enough...