Nature news runs some very readable articles on climate science, but is unfortunately behind a paywall. Which is a shame because they really should be widely read. Here’s a couple of recent beauties:
The Real Holes in Climate Science, (published 21 Jan 2010) points out that climate change denialists keep repeating long debunked myths about things they believe undermine the science. Meanwhile, in the serious scientific literature, there are some important open questions over real uncertainties in the science (h/t to AH). These are discussed openly in the IPCC reports (see for example, the 59 robust findings and 55 uncertainties listed in section 6 of the Technical Summary for WG1). None of these uncertainties pose a serious challenge to our basic understanding of climate change, but they do prevent absolute certainty about any particular projection. Not only that, many of these uncertainties suggest a strong application of the precautionary principle, because many of them suggest the potential for the IPCC to be underestimating the seriousness of climate change. The Nature News article identifies the following as particularly relevant:
- Regional predictions. While the global models do a good job of simulating global trends in temperature, they often do poorly on fine-grained regional projections. Geographic features, such as mountain ridges, which mark the boundary of different climatic zones, occur at scales much smaller than the typical grids in GCMs, which means the GCMs get these zonal boundaries wrong, especially when coarse-grain predictions are downscaled.
- Precipitation. As the IPCC report made clear, many of the models disagree even on the sign of the change in rainfall over much of the globe, especially for winter projections. The differences are due to uncertainties over convection processes. Worryingly, studies of recent trends (published after the IPCC report was compiled) indicate the models are underestimating precipitation changes, such as the drying of the subtropics.
- Aerosols. Estimates of the effect on climate from airborne particles (mainly from industrial pollution) vary by an order of magnitude. Some aerosols (e.g. suphates) induce a cooling effect by reflecting sunlight, while others (e.g. black carbon) produce a warming effect by absorbing sunlight. The extent to which these aerosols are masking the warming we’re already ‘owed’ from increased greenhouse gases is hard to determine.
- Temperature reconstructions prior to the 20th century. The Nature News article discusses at length the issues in the tree ring data used as one of the proxies for reconstructing past temperature records, prior to the instrumental data from the last 150 years. The question of what causes the tree ring data to diverge from instrumental records in recent decades is obviously an interesting question, but to me it seems to be of marginal importance to climate science.
The Climate Machine, (published 24 Feb 2010) describes the Hadley Centre’s HadGEM-2 as an example of the current generation of earth system models, and discusses the challenges of capturing more and more earth systems into the models (h/t to JH). The article quotes many of the modelers I’ve been interviewing about their software development processes. Of particular interest is the discussion about the growing complexity of these models, once other earth systems processes are added: clouds, trees, tundra, land ice, and … pandas (the inclusion of pandas in the models is an in-joke in the modeling community) . There is likely to be a limit to the growth of this complexity, simply because the task of managing the contributions of a growing (and diversifying) group of experts gets harder and harder. The article also points out that one interesting result is likely to be an increase in some uncertainty ranges from these models in the next IPCC report, due to the additional variability introduced from these additional earth system processes.
I would post copies of the full articles, but I’m bound to get takedown emails from Macmillan publishing. But I guess they’re unlikely to object if I respond to emails requesting copies from me for research and education purposes…