On the opposite end of the spectrum from climate deniers are voices predicting that abrupt and irreversible climate change will cause collapse or even human extinction in the relatively near future:

First, James Lovelock, who is best known for the Gaia Hypothesis:

Lovelock believes global warming is now irreversible, and that nothing can prevent large parts of the planet becoming too hot to inhabit, or sinking underwater, resulting in mass migration, famine and epidemics. Britain is going to become a lifeboat for refugees from mainland Europe, so instead of wasting our time on wind turbines we need to start planning how to survive. To Lovelock, the logic is clear. The sustainability brigade are insane to think we can save ourselves by going back to nature; our only chance of survival will come not from less technology, but more.

Nuclear power, he argues, can solve our energy problem – the bigger challenge will be food. “Maybe they’ll synthesise food. I don’t know. Synthesising food is not some mad visionary idea; you can buy it in Tesco’s, in the form of Quorn. It’s not that good, but people buy it. You can live on it.” But he fears we won’t invent the necessary technologies in time, and expects “about 80%” of the world’s population to be wiped out by 2100.

Second, former University of Arizona ecology professor Guy McPherson. This is part of a long, rambling article that cites a lot of evidence, although most of it is newspaper and magazine articles, lecture notes and videos, rather than published peer reviewed articles:

On a planet 4 C hotter than baseline, all we can prepare for is human extinction (from Oliver Tickell’s 2008 synthesis in the Guardian). Tickell is taking a conservative approach, considering humans have not been present at 3.5 C above baseline (i.e., the beginning of the Industrial Revolution, commonly accepted as 1750). I cannot imagine a scenario involving a rapid rise in global-average temperature and also habitat for humans. Neither can Australian climate scientist Clive Hamilton, based on his 17 June 2014 response to Andrew Revkin’s fantasy-based hopium. According to the World Bank’s 2012 report, “Turn down the heat: why a 4°C warmer world must be avoided” and an informed assessment of “BP Energy Outlook 2030” put together by Barry Saxifrage for the Vancouver Observer, our path leads directly to the 4 C mark. The conservative International Energy Agency throws in the towel on avoiding 4 C in this video from June 2014 (check the 25-minute mark). The 19th Conference of the Parties of the UN Framework Convention on Climate Change (COP 19), held in November 2013 in Warsaw, Poland, was warned by professor of climatology Mark Maslin: “We are already planning for a 4°C world because that is where we are heading. I do not know of any scientists who do not believe that.” Among well-regarded climate scientists who think a 4 C world is unavoidable, based solely on atmospheric carbon dioxide, is Cambridge University’s Professor of Ocean Physics and Head of the Polar Ocean Physics Group in the Department of Applied Mathematics, Dr. Peter Wadhams (check the 51-second mark in this 8 August 2014 video), who says: “…the carbon dioxide that we put into the atmosphere, which now exceeded 400 parts per million, is sufficient, if you don’t add any more, to actually raise global temperatures in the end by about four degrees.” Adding to planetary misery is a paper in the 16 December 2013 issue of the Proceedings of the National Academy of Sciences concluding that 4 C terminates the ability of Earth’s vegetation to sequester atmospheric carbon dioxide.

I’m not sure what it means to plan for 4 C (aka extinction). I’m not impressed that civilized scientists claim to be planning for it, either. But I know we’re human animals, and I know animals require habitat to survive. When there is no ability to grow food or secure water, humans will exit the planetary stage.