Politicians in Paris will try, if that’s not too kind a word, to find an agreement that will hold down temperature increases to 2 degrees C above pre-industrial levels [+2C].

Still too much, says James Hansen, of NASA (retired) and Columbia University, who has been warning us about this since 1981 or so:

• The last time Earth was +2C, 120,000 years ago, sea levels were 6-8 meters higher than today. 2 degrees would lock that in, the only question being how fast we would get there.

• It could well be quite fast: satellite data show that ice sheets keep shrinking faster than glaciologists had predicted, and this is consistent with paleoclimate evidence. If the acceleration continues, we can see sea level rise of “several meters” (those younger than me can place bets on more precise numbers, and hope to colect), and coastal cities becoming unusable, within 40-50 years.

• Keeping below 2 degrees is technically feasible and the economic costs would be low – the problem is a political one of getting a simple, revenue-neutral carbon tax.

• Oh, and, yay nuclear power.

For more detail:
[Hansen in Australian radio interview]
[Transcript of interview, and discussion, on Eli Rabett’s blog]

(And, yes, the Statue of Liberty graphic at the top does imply a sea level rise of far greater than 8 meters, since the tip of the torch is 96 meters above mean sea level. Lady Liberty is a cheap and simple emoticon, standing in for messy facts like the problems of keeping subways and sewage treatment working. Below: a New York subway station during tropical storm Sandy in 2012. Now picture the storm surge if the starting mean sea level is a few meters higher than today.)