Q&A On Two Climate Science Questions – A Contribution By Kevin Trenberth

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Kevin Trenberth of NCAR.  As written at the NCAR website

Dr. Kevin E. Trenberth is a Distinguished Senior Scientist in the Climate Analysis Section at the National Center for Atmospheric Research. From New Zealand, he obtained his Sc. D. in meteorology in 1972 from Massachusetts Institute of Technology. He was a lead author of the 1995, 2001 and 2007 Scientific Assessment of Climate Change reports from the Intergovernmental Panel on Climate Change (IPCC), and shared the 2007 Nobel Peace Prize which went to the IPCC…….He is a fellow of the American Meteorological Society (AMS), the American Association for Advancement of Science, the American Geophysical Union, and an honorary fellow of the Royal Society of New Zealand. In 2000 he received the Jule G. Charney award from the AMS and in 2003 he was given the NCAR Distinguished Achievement Award. He edited a 788 page book Climate System Modeling, published in 1992 by Cambridge University Press. He has published over 470 scientific articles or papers, including 47 books or book chapters, and over 206 refereed journal articles and has given many invited scientific talks as well as appearing in a number of television, radio programs and newspaper articles. He is listed among the top 20 authors in highest citations in all of geophysics.

The Q&A with Kevin follow:

1. Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Kevin’s Answer

Global warming usually refers to the human influence on climate.  Some think it refers to just global temperatures.  It doesn’t.  A good indicator is rise in sea level. It is but one component of climate change but the most predictable part and a dominant component on a 20 year time horizon and longer.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Kevin’s Answer

Not a very well posed question. Global climate models deal with all time scales. ENSO is predictable for up to a year or so.  The NAO is largely a natural atmospheric mode and has limited predictability of a few weeks. The PDO is not independent of ENSO and it depends on what is meant by “PDO”.  If it is truly “decadal” then it has persistence predictability for 5 years or so. Climate models have varying degrees of success in simulating these and prediction requires initialization of the ocean and other climate components.  That is very much experimental science but there is considerable promise, as outlined in a recent article in BAMS by Jim Hurrell and colleagues (which you wrote a comment on that failed to impress me).  The ability of models to deal with modes and regional climate is part of chapter 14 of the next IPCC report.  There is promise, but models need to improve.

Postscript:  The Hurrell et BAMS paper and my Reply, that Kevin refers to, is available from

James Hurrell, Gerald A. Meehl, David Bader, Thomas L. Delworth, Ben Kirtman, Bruce Wielicki Bulletin of the American Meteorological Society, 2009: A Unified Modeling Approach to Climate System Prediction; Volume 90, Issue 12 (December 2009) pp. 1819-1832

Pielke Sr., R.A., 2010: Comment on ” A Unified Modeling Approach to Climate System Prediction”, Bull. Amer. Meteor. Soc.,  91, 1699–1701, DOI:10.1175/2010BAMS2975.

with my weblog post discussing this at

Publication Of “Comments on ‘A Unified Modeling Approach to Climate System” By R. A. Pielke Sr And “Reply” By Hurrell Et Al 2010

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