date: Thu Oct 15 14:41:39 2009 from: Tim Osborn subject: guidance for weather extremes to: b.rastgi@uea, p.sanderson@uea, j.lockhart@uea Hi Bharat, Paul and James, as requested, here's a little more guidance about the topic of "Extreme weather events have become more frequent as a result of greenhouse gas induced climate change", specifically about evidence *against* this statement. First, don't get too hung up about trying to find articles that explicitly conclude that there are no changes in extreme weather events driven by GHG-induced climate change. The statement you are debating is very firm; it says "have" rather than "may have". So, to argue against the statement you don't have to prove that weather events have not changed in frequency, you can simply argue that the proof that they have changed in frequency due to GHGs is inconclusive. This may be because observed changes in frequency are too small to be statistically significant, or that causes other than GHGs have not been ruled out. For the latter, some European extremes changes may be linked to changes in the NAO (which is not strongly linked to GHGs) and thus that natural atmospheric fluctuation may explain many of the changes instead of a trend due to GHGs. See: Scaife et al., 2008: Scaife A.A., Folland, C.K., Alexander, L., Moberg, A. and Knight, J.R., 2008: European climate extremes and the North Atlantic Oscillation. J Clim, 21(1), 72-83. doi: 10.1175/2007JCLI1631.1 A couple of studies that showed some extremes are not changing in frequency or show unexpected mixes of increases and decreases and hence no clear/simple link to GHG-induced climate change: AU: G. M. Griffiths AU: M. J. Salinger AU: I. Leleu TI: Trends in extreme daily rainfall across the South Pacific and relationship to the South Pacific Convergence Zone SO: International Journal of Climatology VL: 23 NO: 8 PG: 847-869 YR: 2003 Robson, 2002; Alice J. Robson, Evidence for trends in UK flooding, Phil. Trans. R. Soc. Lond. A July 15, 2002 360:1327-1343; doi:10.1098/rsta.2002.1003 Author(s) Fowler, Hayley Jane Kilsby, Christopher Gerard Journal title International Journal of Climatology Year 2003 Volume 23 Issue 11 Pages 1313-1334 Hope that helps, Tim