The floods will return to Earth


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In our planet’s distant past, there were times when the poles ceased to exist and the average temperature was even tens of degrees higher than today. Conditions that, in several hundred million years, will repeat themselves as the Sun shines with increasing intensity.

However, little is known about how the atmosphere and climate behaved during those long periods of extreme heat. For this reason, a team of researchers from Harvard University has carried out a series of simulations, and in them they found that the Earth could then have experienced intense periods of drought followed by huge storms thousands of km wide and capable of throwing , in just a few hours, up to half a meter of rain. The study has been published in the journal
‘Nature’
.

“If you look at it, somewhere in today’s tropics it is always raining,” explains Jacob Seeley, from Harvard’s Department of Earth and Planetary Sciences and first author of the paper. “But we discovered that in extremely hot climates, there could be several days without rain nowhere over a large percentage of the ocean. And then all of a sudden a massive storm would break out over most of the domain, dumping an enormous amount of rain. Then everything would calm down for a couple of days and the cycle would repeat itself. “

“This episodic cycle of floods,” says Robin Wordsworth, lead author of the study, “is a completely new and unexpected atmospheric state.” The research not only sheds light on the distant past and distant future of the Earth, but also it can also help to understand the climates of exoplanets orbiting distant stars.

This is how the flood occurs

In their atmospheric model, Seeley and Wordsworth raised the ocean surface temperature to 54.4 degrees, either by adding more CO2, (64 times the current amount in the atmosphere), or by increasing the Sun’s brightness by about 10 percent. hundred. And they found that amazing things start to happen in the atmosphere at those temperatures.

When the air near the surface becomes extremely warm, the absorption of sunlight by atmospheric water vapor heats it up low and forms what is known as an ‘inhibition layer’, a barrier that prevents convective clouds. rise into the upper atmosphere to form rain clouds. So all that evaporation gets ‘stuck’ in the layers of the atmosphere closest to the surface.

At the same time, clouds form in the upper atmosphere, above the inhibition layer, as heat is lost to space. The rain produced in those high clouds evaporates before reaching land, returning all that water to the system.

“It’s like charging a huge battery,” says Seeley. “We have a lot of cooling in the upper atmosphere and a lot of evaporation and heating near the surface, separated by this barrier. heat and moisture from the surface entering the cold upper atmosphere will cause a huge storm. “

Which, according to the study, is exactly what happens. After several days, evaporative cooling from upper atmosphere rain storms erodes the barrier, causing a deluge of several hours. In their simulation, the researchers observed more rainfall in six hours than some tropical cyclones do in the US over several days.

After the storm, the clouds dissipate and the precipitation stops for several days while the atmospheric battery recharges to start a new cycle.

“Our research,” Seeley continues, “shows that there are still many surprises in the climate system. Although a 30-degree rise in sea surface temperature is much more than is predicted for human-caused climate change, push atmospheric modeling into unfamiliar territory can provide clues as to what the Earth is capable of. “

“This study – concludes Wordsworth – has revealed a new physics rich in a climate that, from a planetary perspective, is only a little different from the present Earth. It raises big new questions about the climatic evolution of the Earth and other planets, questions in which we will work for many years. “

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