date: Wed Apr  1 13:14:41 2009
from: Phil Jones <p.jones@uea.ac.uk>
subject: RE: Effect of human activity upon global warming
to: "Lucy and Dom" <lucydom@optusnet.com.au>

    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
   ----------------------------------------------------------------------------

