Invitation On Assessing Three Climate Hypotheses

I presented the post

My Further Response To Real Climate’s Gavin Schmidt and Eric Steig

where Gavin Schmidt responded with respect to my placement of him as accepting the CO2-dominated human climate forcing perspective in the following exchange on Real Climate

Gavin – You accept Hypothesis 2b. Thank you for answering clearly. Our EOS paper concluded otherwise, and it is informative to have a discussion by your readers of the three hypotheses on Real Climate. I look forward to reading them.

[Response: Please do not put words into my mouth. First of all, I do not recognise your statements as hypotheses in any useful sense. Secondly, I see no contradiction in accepting that there are multiple sources of anthropogenic influences on climate (I think we will have over a dozen independent effects in the AR5 simulations we are doing), and acknowledging that because of the rate of the rise and the perturbation lifetime of CO2 emissions that they are the dominant issue moving forward. However that does not imply that only CO2 emission cuts are useful, and if you look at any of our recent policy-related work (Shindell et al, 2009; Unger et al, 2009), you will see a portfolio approach to calculating the impact of specific policies and sectors. See also this piece in Physics World. Thus neither 2a nor 2b properly encompass my views. Other forcings are neither negligible nor is CO2 just one issue among the rest. – gavin]

The three hypotheses that we presented in

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R.
Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W.
Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,
J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate
change: The need to consider human forcings besides greenhouse gases
Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American
Geophysical Union


Hypothesis 1: Human influence on climate variability and change is of minimal importance, and natural causes dominate climate variations and changes on all time scales. In coming decades, the human influence will continue to be minimal.

Hypothesis 2a: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern  during the coming decades.

Hypothesis 2b: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2. The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades.

Here is my invitation to readers of my weblog.  What different distinct hypotheses could be written that would be an improvement, if possible, on what we presented in our paper? The 19 co-authors of our EOS paper discussed the three hypotheses above and concluded they are well posed, but what are your conclusions on this issue?

Please send to me at, with your name and affliation, and I will post after obtaining a selection. If you conclude our existing hypotheses are appropriate, however, please e-mail me to report this also.

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