It doesn’t take much of an increase in global temperatures in order to have dramatic effects on the local scale. The extreme weather events that have dominated the headlines in recent years are being influenced by just slightly more than 1°C (2°F) of warming over the entire globe since 1880. By the end of this century, on the more realistic side, it is hoped future warming will be kept to around 2-2.4°C (3.6-4.3°F). Earth has been significantly warmer in the distant past, though, than even these projected values for 2100. How would the climate behave in such a “hothouse Earth” regime? According to researchers from Harvard University, it would be dominated by intermittent dry periods followed by massive rain events.
In order to investigate this very different climate, the researchers used an atmospheric computer model, not unlike the ones used to forecast the weather currently. However, into this model they input some scorching sea surface temperatures of 32-57°C (89-134°F) and also increased the Sun’s brightness by 10%.
At first, the model showed relatively quiet, stable conditions. After several days passed within the model, though, massive rainstorms erupted that were hundreds of miles long and that could dump a foot of rain in just a few hours. Then it would be dry again for a few days, before the cycle repeated.
The reason for this intermittent extreme rainfall is that when the air right near the surface becomes very warm and moist, the water vapor in this layer absorbs sunlight very efficiently. All of the heat and moisture gets trapped by a layer, called the inhibition layer, a little further up from the surface, which works to prevent any convective storms from forming. Meanwhile, radiative cooling in the upper atmosphere causes clouds and light rain to form which eventually erodes the inhibition layer allowing all of the surface energy and moisture to release.
Thankfully, such an extremely warm environment is not expected on Earth anytime soon, but understanding such a scenario enables scientists to understand how Earth’s atmosphere worked in the distant past, and also how the climate may function on planets waiting to be discovered.