date: Thu Oct 15 14:41:39 2009
from: Tim Osborn <t.osborn@uea.ac.uk>
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
