Hi Raoul

For a while I've wondered about how the Earth will end up over the next billion years - ever since I read Lovelock's first paper on the end of the biosphere in the next 0.1 billion years. Then Kasting & Caldeira modifed that claim somewhat - the CO2 crisis would begin about 0.5 Ga from now when C3 photosynthesis begins failing as the partial pressure of CO2 drops to just 100 ppm.

Date Set for Desert Earth

Both models assumed cloudless atmospheres, but it's hard to model what clouds will do as the Earth warms up. A best guess is they may extend the biosphere's lifespan by 0.5 Ga to 2.0 Ga, but we can only guess.

Then there's geophysical changes to 'worry' about. A few years back some Japanese researches came up with this scenario...

Leaking Earth Will Run Dry

...over a billion tons of water, net, is subducted into the mantle each year never to return. Thus Pangaea II might be a LOT bigger than Scotese's little maps show because the sea level might have dropped 500 metres or so.