James Lovelock, father of the Gaia Hypothesis and foremost representative of the OMFG we're all totally f*cked!!1! school of green thinking:
In Lovelock's view, the scale of the catastrophe that awaits us will soon become obvious. By 2020, droughts and other extreme weather will be commonplace. By 2040, the Sahara will be moving into Europe, and Berlin will be as hot as Baghdad. Atlanta will end up a kudzu jungle. Phoenix will become uninhabitable, as will parts of Beijing (desert), Miami (rising seas) and London (floods). Food shortages will drive millions of people north, raising political tensions. "The Chinese have nowhere to go but up into Siberia," Lovelock says. "How will the Russians feel about that? I fear that war between Russia and China is probably inevitable." With hardship and mass migrations will come epidemics, which are likely to kill millions. By 2100, Lovelock believes, the Earth's population will be culled from today's 6.6 billion to as few as 500 million, with most of the survivors living in the far latitudes -- Canada, Iceland, Scandinavia, the Arctic Basin. Read more from David at the Grist