Tuesday, April 10, 2012


date: Thu Oct 15 14:41:39 2009
from: Tim Osborn <t.osbornatXYZxyz.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,

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