Brad deLong just pointed to an article about an interview with Marty Weitzman, an economist who apparently continues to peddle the notion that climate-change-related effects are very uncertain and catastrophic effects very unlikely, but we should do something because the costs of such an unlikely event are very large.
Here's what I said:
With regard to Weitzman: This might have been a valid point 10 years ago. Instead, the science has moved on far beyond the 2002 assessment codified as "conservative conclusions" in the 2007 IPCC report. So let's summarize:
1. IPCC was not the most likely scenario, merely the minimum scenario of which they could be scientifically certain. Better assessments have shown that 400 ppm corresponds to an increase of 1 degree F beyond what has happened now globally and 14 degrees in the Arctic, causing a cascade of effects which 3 million years ago resulted in a 100-foot rise in sea level. This would wipe out at least 1/2 the Earth's arable land (in deltas).
2. It will effectively not be possible to return to a 350 ppm (similar to 1990) climate within the next 1000 years.
3. The follow-on effects of Arctic melting (e.g., more albedo-related absorption of the sun's heat) will lead to an additional 1 degree F heating due to permafrost melt within the next 70 years, with an additional 1 degree possible from methane release.
4. Increased water vapor absorption in the atmosphere leads to an increase of perhaps 10 feet higher storm surge and double the wind power of storms per 1 degree Celsius, as already reflected in Hurricane Sandy and to some extent in recent tornadoes. Movement of the "temperate zone" north in the next 40 years leads to catastrophic drought over almost all of the area from Canada/Soviet Union south to about Argentina/South Africa. As in the Dust Bowl, periodic torrential rains merely bounce off the hard dirt. Loss of snow cover removes much of the runoff for agriculture, with aquifers now in danger from over-use. Present projections are that this will occur by between 2050 and 2070.
5. Following on to the September melting of the Arctic ice cap on or before 2016, accelerated Greenland and West Antarctic melting leads to a rise in sea level of 1 foot by 2050 and 15 feet by 2100. The 100-foot rise in sea level would therefore occur by about 2200.
6. Failure to cut carbon emissions in absolute terms compared to today (that includes the 4.2 reduction by the US -- pathetically inadequate -- over 2008-2011 and the more-than-offsetting increase by China) will lead to 1000 ppm by 2100. Reaching 550 ppm would lead to an additional 2 degrees C of warming and reaching 1000 ppm would add almost 2.8 degrees beyond that. We are thus talking about perhaps 13 degrees Fahrenheit rise by 2100, the way we are going. Sea level would therefore be on a track for a total 220-foot rise, while acidification of the oceans would kill off most sea species and foster iron blooms that might periodically release toxic sulfur fumes on sea-bordering land.
7. "Adaptation" is not a solution by itself, and especially because we are consistently finding solutions that are outdated by the time they are implemented. Cf., again, Sandy and the proposed fixes. Extremely rapid "mitigation" -- reduction in absolute terms of carbon emissions -- is the only thing that will avoid a situation worse than the one described in 1-4, and somewhere around 2035 the "business as usual" scenario cited in 5 and 6 above becomes the most likely outcome, if we continue as we are.
8. Natural gas (due to methods of production) yields very little mitigation. Nuclear power is not feasible on a large scale in the next 20 years, and will have difficulties with sea rise and water temperature rise. Use of all tar sands and oil shale will not only create a worse picture than the one I have painted for 2100, but will put us in serious danger of a "runaway greenhouse gas" effect that would end all life on Earth forever (cf. Venus).
9. Under "business as usual", today's 0.1% decrease in world GNP growth per year due to climate change would reach the 2-3% level by about 2060, due especially to loss of food supply, but also to governmental coping with disaster. From then on, the world's economy (including in developed countries) would decrease and the ability of the world to take action about climate change will also decrease.
10. There is one possible "magic bullet" (injection of sulfur in the air) via geoengineering, but it would have serious health side-effects and would need to be calibrated and escalated for the next 1000 years, at best.
I repeat, 1-4 is the minimum scenario and 5-10 the presently most likely scenario. And by misrepresenting the science by casting things in terms of "very low risk of anything bad happening", Weitzman makes his economic analysis wrong and useless.
If you want a reasonable summary of the science, Joe Romm at www.climateprogress.com is probably as close as you're going to get. Rather than quoting Weitzman as if he offered any useful economic analysis, I suggest that you think carefully about what Joe is saying and develop your own economic analysis.
I suppose I have to repeat yet again the obvious: this is the opposite of an excuse to throw up your hands and say it's all hopeless. The longer we delay doing something, the worse it gets, faster and faster.