What are the Most Useful Climate Metrics?

With so much discussion of global warming and climate change, what are the most appropriate metrics with respect to these environmental issues?

As discussed in the 2005 National Research Council Report (see), and illustrated on page 24 of that report, the focus (actually the icon) of global warming and climate change has been the global average surface temperature. As has been discussed several times on this weblog (e.g. see and see), this is a particularly poor climate metric even for global warming.

However, more appropriately, we need to identify those climate variables which significantly affect social and/or environmental issues of importance. This connects directly to the vulnerability paradigm which has been emphasized on the Climate Science weblog (e.g. see).

As examples, for a farmer, the important climate measures include:

1. length of growing season for their particular crops
2. the availability of natural and/or irrigated water for their crops
3. daytime temperatures including extreme heat which affects crop maturation
4. nighttime temperatures including falling below cold thresholds which threatens plant crop morbidity and mortality.
5. soil moisture levels which are required for optimal crop growth.

Each of these climate metrics are intimately related to local surface temperatures.

We examined several aspects of local 20th century temperature trends, as related to the above climate metrics, in our papers:

Pielke Sr., R.A., T. Stohlgren, L. Schell, W. Parton, N. Doesken, K. Redmond, J. Moeny, T. McKee, and T.G.F. Kittel, 2002: Problems in evaluating regional and local trends in temperature: An example from eastern Colorado, USA. Int. J. Climatol., 22, 421-434.

Pielke Sr., R.A., T. Stohlgren, W. Parton, J. Moeny, N. Doesken, L. Schell, and K. Redmond, 2000: Spatial representativeness of temperature measurements from a single site. Bull. Amer. Meteor. Soc., 81, 826-830.

Thus, can the multi-decadal climate models provide skillful forecasts of the temperature information that is required for these climate metrics?

The CCSP Report has an illuminating response, relative to this question, to one of my comments in my Public Comment (see lines 13-16; page 145 from the Responses to the Public Comment) that I asked on regional prediction skill. In the CCSP Committee response on page 145, lines 24-26, it states

“Owing to natural internal variability, models cannot be expected to reproduce regional patterns of trend over a periods as short as 20 years from changes of radiative forcings alone.”

This statmement, instead of being buried within the 159 page CCSP Response to the Public Comments, should be highlighted as a major conclusion of the CCSP Report which, afterall, is entitled ” Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences “.

If the models cannot even skillfully predict regional linear trends in surface and tropospheric temperatures, how can they be expected to predict the societally and environmentally important local scale climate metrics that are listed earlier in this weblog, and which the farmer needs? If linear trends cannot be predicted, than the models also cannot predict the sudden climate changes (the tipping points) that have been clearly articulated as being important (see).

Thus the answer to the question, “can the multi-decadal climate models provide skillful forecasts of the temperature information that is required for these local climate metrics, as even admitted by the CCSP Committee itself, is clearly NO, on time periods of at least 20 years!

The obvious next question is “on what time periods has there been evidence of regional model prediction skill in these climate metrics?” Addressing this question should have been one of foci of the CCSP Report. Unfortunately, a useful answer to this question was not provided.

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