date: Tue Aug 31 13:06:22 2004 from: Mike Hulme subject: Re: Message for Madeleen Helmer re: the January 2004 nature article to: , Emma and Madeleen, I've read the brief exchange below and Emma has asked me to comment. There are different answers depending on the Qs: "Was the 2003 European heatwave proof that humans are altering climate?" No, although it partly depends on how your audience view "proof". If you are asking this Q a much better place to look for evidence ("proof") is with the global scale surface air temperature trend over 100+ years. Trying to pin evidence for human influence on global climate on *any* discrete weather evident is a pretty poor way to proceed. Much better is focusing on trends (e.g. long-term) and paramaters (e.g. global temperature) where it is easier to define and detect the human fingerprint in a statistical sense. But remember, this will still be "statistical proof" with odds - even if small - on being wrong. Hence IPCC's use of the words likely and v.likely etc. But compare with the standard of evidence in a judicial system. "Was the 2003 European heatwave caused by human-induced climate change?" Sorry, but this again is asking the wrong Q. We are not living with a climate system where one can nicely separate out human-induced weather from natural weather, or at best one again might only do so in a purely statistical sense. I still hold by my original view stated after the 2000 Mozambique floods when I was publicly quoted as saying that there "is no longer any such thing as a natural weather event". The global climate system is already semi-artificial through our perturbation of the atmosphere and so every weather event - extreme or not - is influenced by human actions (just as the floods in Bocastle were exacerbated by human intervention with the river catchment; they weren't "natural"). Of course, one can use clever statistical techniques to talk about likelihoods etc., but the reality is that the climate system is too complex for simple cause-effect relationships, or again at best one needs to recognise that causal explanations can co-exist at multiple levels and depending on which level you invoke the human influence will be more or less evident. In any case, why do people ask this Q? Sure, it is good for headline grabbing and perhaps for public communication activities, but serious strategic planning and investment does not need a definitive answer to it. For these latter applications all we need to know is the general direction of future trends of any given weather/climate parameter - for some applications this information may be needed in formal probabilisitic terms; for other applications much more generalised statements about increased heatwaves and more intense hurricanes may be sufficient. Is this at all useful, or can you narrow down your Q to something that needs a different response? Mike At 19:57 02/08/2004 +0100, you wrote: Hi Mike Could you possibly help me? I was discussing with Madeleen Helmer (Director of the Netherlands Red Cross) whether or not there was yet conclusive proof that the heat wave last summer could be conclusively attributed to human-induced climate change or not (see discussion below). I said that my understanding of the science is that it cannot as we need to have a long term trend before we can make such statements. Madeleen has responded below and I would very much appreciate your comments on this. Many thanks Emma PS If you think this could be a useful email discussion we could copy it to those who might be interested e.g. tyn.building as well as Madeleen and Maarten? -----Original Message----- From: Helmer, Madeleen [[1]mailto:MHelmer@redcross.nl] Sent: 25 July 2004 14:16 To: e.tompkins@uea.ac.uk Cc: Maarten van Aalst (E-mail) Subject: RE: Message for Madeleen Helmer re: the January 2004 nature article Dear Emma, I´m not a scientist but I read articles like these like I read the IPCC reports and alike which are also full of likelies and very likelies. However, a ´likely´ is very different from an ´unlikely´. Both have a margin of uncertainty which is inherent to the subject and the margins of scientific evidence. I understand that from scientists, but when ´likelies´ are communicated by scientists with too much caution, the general public might interpret a ´likely´ as an ´unlikely´, which too my view has happened in the climate change debate in the 1990-ies. This research and article has, to my knowledge not been challenged as being ´unlikely´. For instance the Netherlands Met office gave recently a presentation that confirmed these findings. I look forward to hear what Mike Hulme will say. See also a few more popular articles that came after the Nature publication. (source www.climateark.org Discussing the translation of scientific uncertainties to the general public is one of my favourite debates. So I´m looking forward to the continuation of this debate (and staying in touch with you in general...) best wishes, Madeleen Helmer Head Red Cross/Red Crescent Climate Centre Netherlands Red Cross PO Box 28120 2502 KC The Hague The Netherlands Phone: +31 (0)70 44 55 703 Fax: +31 (0)70 44 55 712 Cell: +31 (0)6 13 55 86 88 E-mail: mhelmer@redcross.nl [2]www.climatecentre.org -----Oorspronkelijk bericht----- Van: Emma L. Tompkins [[3]mailto:e.tompkins@uea.ac.uk] Verzonden: woensdag 21 juli 2004 20:09 Aan: Climatecentre Onderwerp: Message for Madeleen Helmer re: the January 2004 nature article Dear Madeleen Hello, I hope you are well and had a good trip back. After our conversation I returned to the January 2004 Nature article to check my facts - and I thought I would paste the confusing paragraph (for me) and the concluding one below: 1) the confusing one: "A conclusive analysis such as that in Fig. 2 is not feasible for summer 2003, as there is only one data point so far off the mean. To quantitatively assess the situation, we have estimated its return period. The return period is an estimate of the frequency of a particular event (or its exceedance) based on a stochastic concept. Here we employ a gaussian distribution fitted to JJA temperatures to estimate with respect to a selected reference period (see Methods section for details). With respect to the reference period 1864-2000, a return period of several million years is obtained, but such an excessive estimate based on a short series is dubious. To account for the warming in the last decades, we use a more recent reference period 1990-2002 (with T = 1.25 °C warmer mean temperature, but assuming an unchanged standard deviation). With respect to this climatology, the resulting return period for summer 2003 still amounts to = 46,000 yr. The uncertainty of this estimate is considerable, however, and the lower bound of the 90% confidence interval is = 9,000 yr." 2) the concluding one: "Our results demonstrate that the European summer climate might experience a pronounced increase in year-to-year variability in response to greenhouse-gas forcing. Such an increase in variability might be able to explain the unusual European summer 2003, and would strongly affect the incidence of heatwaves and droughts in the future. It would represent a serious challenge to adaptive response strategies designed to cope with climate change." I think (not being a climate scientist) that there are still too many 'might' and 'maybe' words in this article for me to say confidently that the summer of 2003 can be referred to as an indicator that climate change is happening. I am going to speak to Mike Hulme about it and will get back to you when I have. Emma Reference Nature \ 427, 332 - 336 (22 January 2004); doi:10.1038/nature02300 Nature AOP, published online 11 January 2004 The role of increasing temperature variability in European summer heatwaves CHRISTOPH SCHÄR1, PIER LUIGI VIDALE1, DANIEL LÜTHI1, CHRISTOPH FREI1, CHRISTIAN HÄBERLI2, MARK A. LINIGER2 & CHRISTOF APPENZELLER2 [4]http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v427/n69 72/full/nature02300_fs.html --**----**----**----**----**----**----**-- Dr Emma L. Tompkins Senior Research Fellow Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, U.K. Tel: +44 (0)1603 593910 Fax: +44 (0)1603 593901 Email: e.tompkins@uea.ac.uk Web: [5]http://www.tyndall.ac.uk/research/theme3/theme3_flagship.shtml and [6]http://www.tyndall.ac.uk/research/theme4/summary_t2_42.shtml --**----**----**----**----**----**----**--