I’m reading loads of papers again in preparation for writing my master thesis (which will happen, erm, any day now) and just stumbled on the following in John Weyant’s “A Critique of the Stern Review’s Mitigation Cost Analyses and Integrated Assessment” (emphasis mine):
In the  IPCC report, we see that a large amount of increasingly valuable [greenhouse gas] emissions reductions could be achieved at very modest cost according to almost all top-down economic models and all bottom-up engineering models.[T]hat report indicates that emissions reductions of perhaps 10–15 billion tons of CO2 equivalents (3–4 billion tons of carbon equivalents) per year seem to be available at a cost of less than $20 per ton of carbon ($73 per ton of CO2 ) by 2030. Presumably, about half this potential would be achievable for half the cost. Thus, under most baseline emissions projections, we will not completely stabilize atmospheric concentrations of [greenhouse gasses] by capturing all of these low-cost mitigation options by 2030 or 2050, but we will be well on our way. Why not go after these easy targets here and now and at the same time prepare to do the heavy mitigation that will be required later in the century? Obviously, there is uncertainty about what the relatively low-cost mitigation potential actually is, but there is much less uncertainty about this than the total cost of achieving a particular stabilization target. Why frame the policy debate as an all-or-nothing choice where mitigation costs are either so low that we commit immediately to rapid achievement of a stringent climate policy target for the whole century or they are so high that we do almost nothing? It is ironic that those who criticize beneﬁt-cost analyses that suggest a more gradual phasing in of emissions reductions than recommended by the Review seem not to appreciate that we are, in fact, not yet doing nearly as much as those analyses have suggested for several decades.
That, all in all, is the most sensible paragraph I’ve read so far about how much to do in the immediate future (say, after the commitment period of the failure that is the Kyoto protocol runs out in 2012). Sure, the uncertainties are still orders of magnitude large in some cases and it would be foolish to go all out immediately and of course equally foolish to just ignore what we already know, however shaky that understanding may still be, and do nothing. There are plenty of low-hanging fruit to be picked (see the graphic below).