1. Romm’s faith in model results is not warranted, as noted in my previous post.
2. Romm’s argument is that in recent years annual emissions have been higher than assumed in the IPCC’s worst case (A1FI) scenario, and that we are on track to get to 1,000 ppm in 2100. However, instead of looking at emissions it might make more sense to look at real measurements of atmospheric CO2 concentrations for two reasons. First, CO2 concentrations are more directly related to the greenhouse effect. Second, using measured atmospheric CO2 concentrations short circuits two layers of modeling which themselves are major sources of uncertainty, namely, estimating global emissions and, then, estimating the atmospheric CO2 concentrations (based on complex models of the global carbon cycle).
3. What do recent CO2 measurements tell us? If we assume that CO2 concentration (not emissions) will grow (compounded) from 2007 to 2100 at the same annual rate as it did between 2000 and 2007, then CO2 will increase to 636 ppm in 2100 (calculated using data from NOAA). Also, assuming that the other greenhouse gases effectively increase equivalent CO2 by 20 percent (per the ratio calculated for 2005 in the IPCC’s Fourth Assessment Report; see p. 204 [pdf]), we get a CO2 equivalent concentration of 763 ppm in 2100. So, empirical information suggests a much lower future CO2 concentration than Romm fears.
4. In any case, the impact estimates that I presented in my previous post were based on the worst case (A1FI) scenario which, according to the HadCM3 model, would increase CO2 concentrations to 810 ppm in 2085 and 970 ppm in 2100, and cause a 4°C increase in average global temperatures between 1990 and 2085. Despite that, and despite the fact that the impacts were themselves overestimated [pdf], the impacts analyses did not indicate the world would come to an end because of a 4°C increase in global temperature by 2085. Not only that, but the impacts of climate change were overshadowed by other factors (e.g., hunger, malaria, unsafe water, and other poverty-related problems). If climate change terrifies Romm, why is he not petrified by these other problems?
5. Romm is so focused on climate change that he overlooks other problems that are not only much worse, and whose existence is indisputable, but which are also more amenable to solution. This, of course, is a very human failing: Lots of people believe that the problems they work on are more important than others.
6. Romm assumes that a stabilization level of 450 ppm for CO2 is the correct target. What is the basis for this claim? What precise impacts would be avoided if we hit 450 vs. 1,000 ppm? How does he know that the costs of getting to this level would be justified?
7. An earlier fast-track assessment (FTA) sponsored by the UK Government and undertaken by essentially the same group of scientists that produced the analysis that I reported on in my previous post compared the impacts of climate change for three cases: unconstrained (business as usual, BAU) emission case, CO2 stabilization at 750, and stabilization at 550 ppm. Surprisingly, for several categories of impacts (e.g., hunger, malaria, water stress, forested area), stabilization at 550 ppm made matters worse compared to stabilization at 750 ppm! For example, stabilization at 750 ppm reduced the total population at risk (PAR) for malaria in 2085 by a greater amount (1.3% below the BAU case) than stabilization at 550 ppm (0.4% below BAU). (See Goklany, IM (2005), “A Climate Policy for the Short and Medium Term: Stabilization or Adaptation?” [pdf] Energy & Environment 16: 667-680). Hence, there is no guarantee that stabilizing CO2 at 450 ppm would optimize human or environmental well-being. For all we know, stabilizing at 750 may be more optimal. Before advocating policies to get us to 450 ppm, at a minimum it ought to be shown that’s a goal worth pursuing, even absent consideration of opportunity costs. Unfortunately, Romm doesn’t do either.