It seems we are all going to die. Or not? However, recent research suggests that this can be done quickly only if we put in some effort …
A long time ago - say, before 2013 - it was believed that the inner boundary of the habitable zone in the solar system was quite far from the Earth, about 0.1 AU. That is, not closer than 0.9 a. e. from the star. Thus, a planet like ours will overheat so that it will begin to lose water from the atmosphere, only after a billion years, but before life nothing threatens.
Recent work by Ravi Kumar Kopparapu's group, using refined data on the absorption of sunlight by carbon dioxide and water vapor, provided very different data. So, it turned out that the inner border of the habitable zone is 0.99 AU. That is, from the Sun, that is, life on the Zemkub walks on very thin ice, which, moreover, will soon melt.
It turned out that in about a hundred million years, the luminosity of the Sun would increase by 1% due to the inevitable features of the local thermonuclear reactions, and the Earth's biosphere would order to live for a long time, most likely without having had time to pass into the noospheric stage.
Still, our ecological frenzy will not bring the planet to 900 ° C: right now, efforts will be required even to bring it to the state of the Mojave Desert. (Here and below illustrations by Ravi Kumar Kopparapu et al., Wikimedia Commons.)
Having received this data, Ravi Kumara Copparapu and his colleagues decided to check the hitherto considered unshakable conclusions of Casting and Ackerman, who in 1986 simulated the consequences of the greenhouse effect on the Earth's climate and came to the conclusion that no increase in the concentration of CO2 in the air would lead to its loss of the hydrosphere. It is really difficult to predict what will happen in 100 million years, because there is still a possibility of a change in the Earth's orbit, but carbon dioxide, as the history of the Anthropocene shows, is already producing well now.
As it turned out using a one-dimensional model of the Earth's climate, in principle, putting an end to life on it by burning fossil fuels, as they say, is achievable. Although not as easy as you thought. Basically, warm-up scenarios fall into two large groups: fast water loss and slow water loss. In the first case, the planet will lose its oceans in about a billion years.
It sounds as if we still have time, but in reality the oceans are very deep, but the water on land can almost disappear much before the seas completely dry out, which is why significant problems such as desertification will begin almost immediately after the beginning of the stage of such a moist greenhouse (wet greenhouse effect).
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Less optimistic is the scenario of a slow farewell to H2O. In this case, ocean water will not be lost so quickly, so the seas will evaporate completely even before the disappearance of water vapor from the gas envelope. And although it seems that it is better with water than without it, in practice such a component in the atmosphere will contribute to enhanced absorption of infrared rays and will lead to an increase in temperature not to some miserable 40-60 ° C, as in the previous version, but immediately up to full 900 ° C!
As you understand, under such a combination of circumstances, the presence of water vapor on the planet can hardly be called happiness, therefore the end will come much faster. This is called inferno runaway greenhouse (rapid greenhouse effect).
The authors of the work believe that, in general, the modeling gave optimistic results - a rapid greenhouse effect is excluded with any increase in the concentration of carbon dioxide.
So, metals on the Earth's surface in the next billion years, most likely, will not begin to melt. But the wet greenhouse effect is available with only an eleven-fold increase in CO2 concentration. Recall that over the entire period from the beginning of the industrial revolution to the present day, the amount of this component in the atmosphere has grown by only 31%, so if you plan to bring the planet to the loss of the hydrosphere, then you cannot do without overindustrialization. Given the weakness of industrial policy in the world today, breathe a sigh of relief.
But it's not that simple. Life, of course, will survive, the authors of the work are doing a favor for life, but the person will be in big trouble. Already at a wet bulb temperature of ~ 35 ° C, we begin to experience hyperthermia, which rarely has a happy ending, especially if you are prone to cardiovascular diseases, because the skin must be two degrees colder than the body in order to effectively transfer heat to environment. If this condition is not met, cooling does not work, and you can forget about, say, running or physical effort. The problem is that even when the amount of carbon dioxide quadruples, such a temperature will seasonally arise in the summer in temperate latitudes, and with an increase of eight it will move even to high ones.
Now it would be good to ask the question, can we, such talented and thoughtless humanoids, burn enough fossil fuels to achieve hyperthermia in mid to high latitudes? It is estimated that, at current fuel prices, economically viable fuel combustion cannot affect all available reserves at all. Some of them are simply too expensive to mine.
Therefore, in today's situation, the maximum increase in the concentration of carbon dioxide will not exceed threefold. That is, if you turn off common sense and turn on coal burning, it will be hot, but not until a history of hyperthermia. True, with a sharp rise in energy prices or the inclusion of methane hydrates in the calculations, which are currently being extracted by Japan, it is in principle possible to achieve a 4–8-fold increase in concentration.
Well, you can still kill yourself if you try very hard. But scientists have found less dubious reasons for joy. In particular, when the cloud cover and incomplete mixing of the Earth's troposphere are taken into account, the inner boundary of the habitable zone in the solar system can be shifted from 0.99 to 0.97 AU. e. And under a relatively favorable scenario for the development of cloud cover in the future, the majority of plants on the planet will be able to engage in photosynthesis for another 350 million years, some - for almost a billion years, although among the most resistant there will be no trees and ferns - only plants with photosynthesis C4, in the bulk is herbs. That is, in the next hundred million years, humanity is not threatened with extinction, although it will not be possible to smoke the sky for too long. Apparently, we are not talking about a billion years before the end of the world:The earth - get ready - will be an unsuitable home for us much earlier.
A is our world today; In … E - he is, but at different moments of the Cretaceous period. As you can see, in some places constant temperature stress for humans existed even then. If the average annual surface temperature exceeds 300 K, hyperthermia geographically sweeps across the planet.
Undoubtedly, the considered work still does not take into account many factors. The researchers themselves say that it would be good to build a more complex three-dimensional model of climate development. And it’s impossible to foresee everything: for example, the disappearance of forests in the next 300–350 million years, obviously, will decently change the albedo of the Earth, which means that it will also affect the climate. The same trees generate clouds over the planet most intensively, so it will clearly be difficult to confidently predict cloudiness after they disappear.
But the presented model for the modern level of knowledge is fully worked out, so that, in principle, it can serve as a guide to action - or, more precisely, a guide to which actions should be avoided.