Remember this? These were some of the impacts expected for various degrees of global warming as described in the Climate Change Committee's report.
;)
Click for full sizeThe source for this table is IPCC WG2 - it's a direct lift from one report to the other. The IPCC report then provides citations for each impact described.
The one near the top - semi-arid/arid areas increase by 5-8% - struck me as interesting. After all, we have heard about the greening of the Sahel, so I was expecting exactly the opposite impact in Africa.
The table in the IPCC report is sourced from this page, which says:
Furthermore, for the same projections, for the same time horizon the area of arid and semi-arid land in Africa could increase by 5-8% (60-90 million hectares). The study shows that wheat production is likely to disappear from Africa by the 2080s.
The citation is not entirely clear, but appears to be Fischer et al 2005, a paper in Phil Trans B, where a similar claim is made:
Under the climate change scenarios considered, and by 2080s, AEZ estimates of arid and dry semi-arid areas in Africa increase by about 5–8%, or 60–90 million hectares.
This in turn cites a paper by the same authors - but unfortunately for the Climate Change Committee it's a non-peer-reviewed article. The title is "Climate Change and Agricultural Vulnerability" and it was written by the International Institute for Applied Systems Analysis. This is a familiar name, but I can't quite recall where I've come across them before.
Here the claim is as follows:
Climate changes, as projected by GCMs for the SRES B2 and A2 emission scenarios in the 2080s, would result in another 580,000 km2 (scenario B2, with a range of 360,000–760,000 km2) and 920,000 km2 (scenario A2, with a range of 850,000–1,025,000km2) of arid and dry semi-arid lands, an increase of 5.4% and 8.5% over current conditions respectively.
Unfortunately that is as far as the trail runs - there is no citation given for the claim. What we can tell, however, is that the claim is based on climate models, and we know already that no climate models have been shown to have any skill at a regional level. I put this to Lord Turner at the RSE and he fully agreed, but said that the uncertainty made action more important not less so.
Wouldn't you love to be the betting shop owner when he walked through the door?
What seems clear to me is that this bit of science is decidedly iffy - certainly it is not fit to inform UK policymaking. I wonder if any of the other impacts in the IPCC table are any more rigorous?