date: Wed Apr 1 13:14:41 2009 from: Phil Jones subject: RE: Effect of human activity upon global warming to: "Lucy and Dom" There are lots of issues that relate to this 90% probability statement. I'd suggest you read Ch 9 of the IPCC Report and/or the Technical Summary. [1]http://ipcc-wg1.ucar.edu/wg1/wg1-report.html You can download the pdfs from the above. One simple way of thinking about this. Climate scientists are 100% confident that they can detect an anthropogenic signal in surface temperature data. Climate models also predict changes in precipitation, but these are much harder to detect in the observations. Another way of thinking about this is - if climate scientists were 100% certain, then we'd know what the climate sensitivity is and we'd know exactly how much temperatures would increase this century (if the greenhouse gas projections were correct). Phil At 13:03 01/04/2009, you wrote: Thanks Phil From this I see that the IPCC report implies there is a 90% probability that human activity has contributed to observed global warming. I find that rather odd though. If the IPCC is not 100% certain that human activity contributes to global warming how can the IPCC know there is a 90% probability that it does have this effect? Any ideas? I agree with your second point observed temperature has warmed unequivocally over the past few decades relative to the 1961-90 mean. Regards Dom ___________________________________________________________________________________ From: Phil Jones [[2]mailto:p.jones@uea.ac.uk] Sent: Wednesday, 1 April 2009 9:52 PM To: Lucy and Dom Subject: Re: Effect of human activity upon global warming Dom, IPCC's likelihood language is defined in the attached. Table 4 is the key to where the CRU use of likely and very likely come from. We used the IPCC statements from Chapter 9 of the 2007 AR4 Report. Unequivocal was used with respect to the observed warming. In the context here this means beyond doubt. Cheers Phil At 12:34 01/04/2009, you wrote: Hi Phil Another question for you if I may. Beneath the graph at [3]http://www.cru.uea.ac.uk/cru/info/warming/ is the following notation: The Inter-governmental Panel on Climate Change in its most recent report in 2007 stated: 'Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.' 'Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations12. This is an advance since the TAR's conclusion that "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations". Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns' I am interested in the use of the words very likelyby the IPCC. Does this mean it has not been proven beyond a doubt that human activity is contributing to global warming? From my reading of the popular media I thought it had been proven that human activity contributes to global warming. Thanks Dominic Mether ___________________________________________________________________________________ From: Phil Jones [ [4]mailto:p.jones@uea.ac.uk] Sent: Thursday, 14 February 2008 2:42 AM To: lucydom@bigpond.com Cc: Sheppard Sylv Miss (SCI) Subject: FW: Global cooling? Dominic, The anthropogenic component of global warming is currently raising temperatures at about 0.2 deg per decade (rounded to one decimal place). Estimate comes from the trend of temperatures over the period from the 1970s in the real world and more importantly from climate models. This change per year is 0.02 deg C per year. This change is quite small given the size of year-to-year variability evident in the historic record of global temperatures. Some of this variability stems from El Nino's and La Nina's, some from the effects of explosive volcanic eruptions, and some from other factors related to internal variability of the climate system (changes in ocean currents and the winds). Whatever the exact reasons, we expect similar rates of year-to-year variability in the future. So there is absolutely no difficulty with the annual global mean temperature values not increasing year on year. 0.02 deg C per year is also small compared to the error of the global temperature estimates. This is about +/- 0.10 at 95% confidence level. As the anthropogenic component is small on the year to year basis, you'd expect to see it more easily on decadal timescales. 2001-2007 is 0.21 deg C warmer than the 1991-2000 period. Cheers Phil -----Original Message----- From: lucydom [ [5]mailto:lucydom@bigpond.com] Sent: Wednesday, February 13, 2008 10:53 AM To: Sheppard Sylv Miss (SCI) Subject: Global cooling? Hi The graph at [6]http://www.cru.uea.ac.uk/cru/info/warming/ seems to suggest the planet has been cooling since 1998. What can explain this obvious downward trend, and how can this recent global cooling be explained within the broader context of global warming? Regards, Dominic Mether Brisbane, Australia Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ----------------------------------------------------------------------------