Comment On Andy Revkin’s Post “More On The ‘Sensitive’ Climate Question” Specifially With Respect To His Interview With Andreas Schmittner

Andy Revkin has an interesting interview with Andreas Schmittner of Oregon State University in an informative post on Dot Earth titled

More on the ‘Sensitive’ Climate Question

I agree with Andreas that

Earth was much different during the last glacial maximum (LGM). Imagine huge ice sheets covering North America and northern Europe, glaciers in the Alps and other mountain regions descending much further down the valleys into the low lands, Europe was essentially without forests and tundra covered much of the northern Hemisphere land masses. Sea level was 120 meters lower than today since more water was locked up as ice on land.

The atmosphere had only 185 ppm [parts per million] CO2 and other greenhouse gases such as methane and nitrous oxide were also lower. There was lots of dust in the air.

He does, not however, emphasize another really major distinction between today’s climate system and that 18000 years ago. The presence of high continental ice sheets in the Northern Hemisphere would substantially alter the wind circulations, including ancient versions of ENSO, the PDO, the NAO ect. Any comparison with a “climate sensitivity” based on a surface global average temperature anomaly tells us little of scientific use in terms of how added CO2 and other greenhouse gases would alter our climate in the coming decades.

Moreover, running global climate models with such a landscape configuration, including a more extended coastline due to the lower sea level, is not a satisfactory comparison with climate change predictions for the current climate system.  Not only is the surface landscape so different, but the LGA time period can not be used to show skillful climate change predictions even IF they were able to accurately simulate the LGA climate system.

My e-mail to Andy with further comments  is reproduced below,

Hi Andy

Thank you for sending. The surface temperature trend is a very poor metric to diagnose global warming and cooling, much less the much broader topic of climate variability and longer term change.

Over land, there are a variety of issues. For example, its value (its anomaly) is a function of the height at which a temperature anomaly is calculated, with the minimum temperature anomaly (which is used to construct the mean temperature anomaly) being a particularly inadequate metric to diagnose global average global warming and cooling.

See my further discussions, for example, in

https://pielkeclimatesci.wordpress.com/2011/09/20/torpedoing-of-the-use-of-the-global-average-surface-temperature-trend-as-the-diagnostic-for-global-warming/

https://pielkeclimatesci.wordpress.com/2011/04/26/repost-of-weblog-climatequotes-com-climate-scientists-answer-question-should-climate-sensitivity-be-measured-by-global-average-surface-temperature-anomaly/

https://pielkeclimatesci.wordpress.com/2011/04/14/climate-science-myths-and-misconceptions-%e2%80%93-post-2-on-the-metric-of-global-warming/

https://pielkeclimatesci.wordpress.com/2011/04/11/climate-science-myths-and-misconceptions-post-1-on-the-global-annual-average-surface-temperature-trend/

as well as in our papers

Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229.

Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2009: Reply to comment by David E. Parker, Phil Jones, Thomas C. Peterson, and John Kennedy on “Unresolved issues with the assessment of multi-decadal global land surface temperature trends” J. Geophys. Res., 114, D05105,  doi:10.1029/2008JD010938.

Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., 114, D21102, doi:10.1029/2009JD011841.

Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2010: Correction to: “An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., 114, D21102, doi:10.1029/2009JD011841″, J. Geophys. Res., 115, D1, doi:10.1029/2009JD013655.

Even with respect to a surface global-annual average temperature change, as Schmittner writes, the “Earth was much different during the last glacial maximum (LGM)”. Thus any scientifically robust conclusions regarding how the present and upcoming climate system will behave based a surface temperature anomaly from that time period is very speculative.

Best Regards

Roger Sr.

P.S. You are, of course, welcome to post my e-mail.

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