The Global Warming Challenge

Evidence-based forecasting for climate change

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Dr. Kevin Trenberth, Keynote Presentation at ISF ‘07

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Dr. Kevin Trenberth, Head of the Climate Analysis Section at the National Center for Atmospheric Research, gave a keynote presentation June 26th, 2007, at the 27th International Symposium for Forecasting. He was a lead author of the 1995, 2001, and 2007 Intergovernmental Panels on Climate Change (IPCC) Scientific Assessment of Climate Change. For a full list of credentials, please visit Dr. Trenberth’s homepage.

Trenberth’s keynote presentation was titled Climate and weather forecasting: Issues and prospects for prediction of climate on multiple time scales. His full presentation is available at his website. The following is an abstract excerpt:

In contrast to weather, which involves the evolution of the atmosphere, climate involves the entire climate system and its forcings. The climate system includes the atmosphere and oceans as fluid components, and all aspects of the land surface including vegetation and hydrology, and the cryosphere. The forcings include influences external to the climate system, such as the sun or human activities. While prediction of the atmosphere is inherently limited by chaotic developments, its systematic interaction with other components of the climate system and forcings enables patterns or the statistics of atmospheric behavior to have some predictability.

What does Dr. Trenberth have to say about Armstrong and Green’s paper?

“The paper by Scott Armstrong and K. C. Green is highly critical of IPCC procedures and “forecasts” for not being based on “evidence based” procedures as outlined in an earlier book of his. It is true that IPCC does not refer to Armstrong’s work as it has dubious relevance. In fact IPCC does not do forecasts, as explained at [Trenberth’s contributions at Nature.com blogs].”

The following is an excerpt from Trenberth’s article “Predictions of Climate” at Nature.com:

“…there are no predictions by IPCC at all. And there never have been. The IPCC instead proffers “what if” projections of future climate that correspond to certain emissions scenarios. There are a number of assumptions that go into these emissions scenarios. They are intended to cover a range of possible self consistent “story lines” that then provide decision makers with information about which paths might be more desirable. But they do not consider many things like the recovery of the ozone layer, for instance, or observed trends in forcing agents. There is no estimate, even probabilistically, as to the likelihood of any emissions scenario and no best guess.

Even if there were, the projections are based on model results that provide differences of the future climate relative to that today. None of the models used by IPCC are initialized to the observed state and none of the climate states in the models correspond even remotely to the current observed climate. In particular, the state of the oceans, sea ice, and soil moisture has no relationship to the observed state at any recent time in any of the IPCC models.”

If you would like to contact Dr. Trenberth, email trenbert at ucar dot edu.

Written by climatebet

June 27th, 2007 at 2:42 am

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