This doesn’t look right. Global temperatures have been a lot higher than what’s depicted here (Paleocene–Eocene Thermal Maximum) and the Earth didn’t turn into an uninhabitable desert. That link is to a time when temperatures were approximately 14 degrees Celsius higher than now!
CORRECTON: I originally wrote “25 degrees Celsius” but that is wrong. The correct value is 25 degrees Fahrenheit, which corresponds to about 14 degrees Celsius.
Edit: https://en.wikipedia.org/wiki/Cretaceous_Thermal_Maximum#/media/File:All_palaeotemps.png. An increase of 4 degrees Celsius would match the climate at the peaks between the cycles of ice ages (last such peak: about 100,000 years ago). The Earth would actually still be colder than it has been most of the time since the origin of life.
This higher-resolution plot on Wikipedia does seem to show an Eemian peak temperature of approximately +4 degrees C. The dataset is the same (EPICA Dome C) so I think that the much longer timescale of the first plot I linked to simply averages out relatively short-term peaks like the Eemian.
With that said, I agree that the modern pace of climate change is much faster than these historical cases, and I share your concern that changing the climate so quickly might trigger something that slow changes didn’t. I’m just saying that most of the Earth isn’t going to become a desert.
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