From
Jeff Wells' terrific
Rigorous Intuition, I was tipped to this
Climate Ark article.
For those of you disinclined to click through and read the short article, I'll provide the gist.
In a nutshell, it is that the Amazon can withstand 2 years of drought before it begins baking to desert. The tallest trees, which provide shade for all of the growth below, can withstand one year of drought. After that, their roots grow deeper to seek out more water. If they don't find any in the second year, they die.
When they die and topple, all of the undergrowth is suddenly exposed to the withering equatorial sun. These are "shade" plants and they quickly die. Finally, the soil bakes.
At every step of this process, some of the CO2 sequestered in the forest is released into the atmosphere. If we lost the carbon sink that is the Amazon, the rate of global warming would increase by 50%.
The Amazon is currently beginning its second year of drought.
Feelin' a little warm?