Two degrees of warming is the point at which up to 4 billion people could suffer water shortages, crop yields could fall in many regions of the poor world, mountain glaciers disappear worldwide and the irreversible melting of the Greenland ice sheet, which could eventually raise global sea levels by 7 metres, is expected to begin. It is also the point at which several important positive feedbacks could be triggered. ... A two-degree rise in temperatures could cause the runaway warming of permafrost throughout the Arctic Circle [which would release methane, leading to more warming, and so on].That seems right: Last month, NASA's James Hansen and 46 other climate scientists published a new paper (PDF) arguing that once carbon concentrations in the atmosphere reach around 450 parts per million (we're currently at 384), the earth will hit a tipping point. And while scientists don't know exactly how high sea levels could then rise, climate records show that, during previous eras in which CO2 was between 350 and 450 ppm, the earth was ice-free and sea levels were 81 feet higher than present. It's a big fucking deal.
For this and other reasons—including the die-back of tropical forest, the accelerating metabolism of soil bacteria, a reduction of the earth’s reflectivity as ice melts—two degrees of manmade warming could cause a total impact of three degrees; and three degrees could lead inexorably to four. In other words, if two degrees of warming takes place, the problem is snatched from our hands. The biosphere becomes a major source of greenhouse gases, and there will be little we can do to prevent further climate change. Two degrees is the only target worth setting. ...
A paper published recently in the journal Climatic Change shows that in order to obtain a 50 per cent chance of preventing the global average temperature from rising by 2° above its pre-industrial level, we require a global cut of 80 per cent by 2050.
The first day [in office], I would get us of Iraq with diplomacy. The second day, I would plan a huge initiative on making America energy independent with an Apollo-like program to become more reliant on renewable fuels. I'd ask the American people to sacrifice in so doing. Third, I would have a major initiative on climate change. Ninety percent .. .. reduce emissions by 2050. The fourth day I would take off.Whether he truly means it or not, I do wish every Democratic candidate would take this tack. Monbiot's right, I think—all other concerns can wait. Is that too "alarmist"? It should be.