An analytical post on The Blackboard has raised again the concern I have with climate analysis based on short-term observations. Climate models tied to long-term historical records are all we really have to go on for understanding the relationship between atmospheric carbon and global temperatures. The models still have lots of limitations, but they are improving constantly as new studies lead to better understanding of the many processes that influence climate.
Two points in response to Lucia's blog post, which assesses temperature trend over the most recent nine-year period.
First, climate scientists contributing to the IPCC reports are well aware of weather cycles and short-term trends. A nine-year trend analysis is simply an interesting short-term observation that contributes little to the veracity of long-term forecasts.
Second, as a throw-away at the end she briefly mentions longer term historic trends as being low and suggests that this, together with her analysis of the nine-year trend, means that future trends will be positive but low. While her analysis of the short term may be rigorous (though I can’t vouch for that), this concluding comment is not presented with any analysis to back it up.
Her final line, "Other than models, there is no evidence the climate trend has increased from historic levels to reach a rate of 2C/century," is curious. This seems to suggest that "evidence" means "observations", since any other form of evidence must be from some kind of model. The very concept of an average global temperature is a model - we cannot simply go out with thermometers and calculate an average over the globe and over a year, without making assumptions about weather systems and the circulation of air.
I am not trying to trash Lucia's analysis, but voicing a cautionary note that whatever we want to believe about climate change, we need to recognize the limitations of analysis. We just need to take the best we have, and go from there.
If you are interested in the implications of climate change for Africa, I highly recommend that you have a look at the new report from the Grantham Institute for Climate Change (Imperial College London), “The science of climate change in Africa: impacts and adaptation”. It provides, I believe, a very rational summary of the current state of understanding of the likely climate impacts for Africa.
The report points out that many of the likely effects of climate change are things that are experienced regularly as a result of normal cyclical variations, and that African communities therefore have much to contribute to the development of adaptation strategies that are essential even if there is no climate change at all. In that respect, one could argue that – at least in Africa – to some extent the whole debate about climate change is a diversion from work that needs to be done to improve lives and livelihoods. We don't only have inter-generational equity to worry about (as in the Brundtland Commission definition of sustainability, which talks of leaving a healthy earth for future generations), but also intra-generational challenges.
An interesting point from the report is that we can already forecast with 70% accuracy whether Zimbabwean maize harvests will fail or not each season. Those farmers, and their markets, need strategies to improve resilience to such shocks. A related point is that “Many crops in Africa are grown close to their limits of thermal tolerance.” (page 11) Which means that even small variations in temperature, even if they are short-term changes caused by El Nino or other factors, can devastate agriculture and food security.
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