The Paleoclimate Implications for Human-Made Climate Change, a draft of a new paper by James E. Hansen and Makiko Sato is available [PDF].
The paper’s abstract:
Milankovic climate oscillations help define climate sensitivity and assess potential human-made climate effects. We conclude that Earth in the warmest interglacial periods was less than 1°C warmer than in the Holocene and that goals of limiting human-made warming to 2°C and CO2 to 450 ppm are prescriptions for disaster. Polar warmth in prior interglacials and the Pliocene does not imply that a significant cushion remains between today’s climate and dangerous warming, rather that Earth today is poised to experience strong amplifying polar feedbacks in response to moderate additional warming. Deglaciation, disintegration of ice sheets, is nonlinear, spurred by amplifying feedbacks. If warming reaches a level that forces deglaciation, the rate of sea level rise will depend on the doubling time for ice sheet mass loss. Gravity satellite data, although too brief to be conclusive, are consistent with a doubling time of 10 years or less, implying the possibility of multi-meter sea level rise this century. The emerging shift to accelerating ice sheet mass loss supports our conclusion that Earth’s temperature has returned to at least the Holocene maximum. Rapid reduction of fossil fuel emissions is required for humanity to succeed in preserving a planet resembling the one on which civilization developed.
After pondering that abstract for a few moments and then skimming the paper, I have to ask: When will humanity learn to see the difference between “alarmism” and “wicked smart people who connect the dots before you do”? This is something I’ve been thinking about quite a bit recently, as I’ve become more convinced than ever that our collective perception of the urgency of our two greatest global challenges — climate change and peak oil — is the biggest single factor controlling the scope and nature of our responses to them.
Some basic facts of these two situations have a remarkable tendency to focus the mind and greatly accelerate the learning process of newcomers to these topics. In peak oil, tell people how much the US, the EU, Japan, etc. depend on oil imports, and not just for transportation, and then show them the statistics on the number of oil producing countries that are well past their peak of production (roughly 70 countries, last time I looked) and point out that we’re doing insane things like drilling 5 miles below the ocean’s surface for oil, or cooking it out of the ground in Canada. The show stopper in climate change, I’ve found, is a toss-up between the “hockey stick graph”, showing temperatures over the last 1,000 years, and explaining how long CO2 stays in the atmosphere. It’s truly amazing to me how many people assume that if we cut all CO2 emissions tomorrow that we’d see atmospheric CO2 levels drop back to pre-industrial levels in a few months to a year. Once they understand the “CO2 ratchet”, and you tell them we’re pouring roughly 30 billion more tons of CO2 into the air every year, at least half of which we’ll have to live with for centuries, they look like a trapped animal.
The longer you study either of our great challenges, particularly climate change, the more dots you connect and the more trouble you realize we’re in. Whether that knowledge sends you fleeing into the open arms of denial or turns you into a climate change crusader is probably more a question of an individual’s personality than anything else. But one thing that’s very clear is how hard it is to talk openly and plainly about these topics with newcomers or even those somewhat less engaged on the topic than your friendly neighborhood energy and climate geek. No matter how you approach the subject you quickly run into a metaphorical fork in the road, with one path marked “don’t sound like a crazy person, hold back on the really scary details, and when someone looks nervous ask if there’s more salsa for the chips”, and the other labeled “give ‘em the unvarnished truth, tell it as plainly and calmly as possible, and trust the listener”. I’m ashamed to say that I’ve often taken the first, easy road in social settings. Since we’re lucky enough to have experts around like Hansen and Sato who apparently see only the second road, I suggest you grab a copy of their paper and read it.
 This is akin to an old joke among computer journalists: When someone calls something a “paradigm shift” it usually means the speaker didn’t see the change coming before it became obvious.
 This is eerily reminiscent of the smoker who assumes that his cancer risk goes to near-zero as soon as he stops smoking, and that mistaken knowledge then leads him to never quite find the willpower to quit.