[rakoo]

If you read the headline carefully, it's the global warming that needs to be reversed before 2000; the disappearance of nations can (and will) happen after.

The reason this is true is that CO2 emissions can't really be reversed; accounting for all forms of "capture" (biomass, sea exchange, calcification) CO2 disappears in a reverse power law way, such that after 10 000 years 10% of it is still there (https://www.yaleclimatemediaforum.org/pics/1210_ZHfig5.jpg)