Vegetation can have
a strong impact on water scarcity.
Because when you have vegetation, it tends to mine the groundwater
and drive it to evaporate, and then recycle to perpetuate rainfall.
And then when the vegetation is gone, the
the water from rainfall just runs off, instead of re-evaporating.
And so vegetation
can provide a kind of tipping point...
where things can hang on, under water stress,
then the vegetation dies,
and it takes even more water to get
back out of the drought than you had originally.
Some examples of rainforests that
are vulnerable include Queensland, Australia,
where the high altitude rainforest
is expected to get chased off the surface of the Earth as the climate zones
warm, because you can't go any higher up
in the mountains to get to a cooler climate.
That's vulnerable under fairly modest amounts of warming.
The big rainforests, the Amazon, and Indonesia,
are in the three degree chapter in
Lynus's book.
it's very speculative and model dependent whether
these rainforests could actually collapse or not.
But it's certainly a possibility.
We know that because the Sahara used to be a rainforest during a time
in the early interglacial time called
the African humid period, about 8,000 years ago.
And it abruptly collapsed,
as diagnosed from pollen records in sediment cores of Africa.
Nebraska used to be sand dunes; it looked like the Sahara.
It's a place now called The Sand Hills.
And these date from medieval time when it was so
dry in the other parts of the American west.
These things are definitely open to change.
One scary possibility is that the end game
for some jungle like the Amazon would probably involve fire.
If the conditions are just wrong and the plants
are not thriving and everything dries out, you could have
big fires that could suddenly release CO2 to the atmosphere
as well as carbon monoxide, and soot,
announcing, and punctuating the demise of such a rainforest.