Further Comment on the Feddema et al. (2005) Science paper “The Importance of Land-Cover Change in Simulating Future Climates”

The Climate Science weblog has commented on the excellent Feddema et al Science paper entitled “The Importance of Land-Cover Change in Simulating Future Climates ” (see , see , and see ).

In response to several e-mails between Dr. Feddema and I, I recommended the following approach to move beyond the metric of a global average surface temperature trend in order to assess the significance of the climate response to land use/land cover change;

“The first thing that is needed is the determination of what metric(s) should be used to determine the relative effects of “global warming” and of the more inclusive term “human caused climate change”. The global mean surface temperature trend has become an icon for this purpose. However, as I will discuss in my NCAR ASP seminar on Wednesday [December 14, 2005] (and have published on), it has major unresolved issues regarding its robustness.

Moreover, it is an inadequate metric to describe how we are altering the climate system, as was emphasized in the 2005 NRC report . The global mean temperature trend, even if it were accurately evaluated, does not inform us how the spatial patterns in the atmosphere, oceans and other components of the climate system are changed as a result of human intervention in the climate system.

We have already proposed two new metrics; one is based on the global averged redistribution of surface sensible and latent heat flux due to LULC change (see Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S. Running, 2002: The influence of land-use change and landscape dynamics on the climate system- relevance to climate change policy beyond the radiative effect of greenhouse gases. Phil. Trans. A. Special Theme Issue, 360, 1705-1719),

while the other is based on the globally-averaged redistribution of aspects of the water cycle such as precipitation (see Pielke, R.A. Sr., and T.N. Chase, 2003: A Proposed New Metric for Quantifying the Climatic Effects of Human-Caused Alterations to the Global Water Cycle. Presented at the Symposium on Observing and Understanding the Variability of Water in Weather and Climate, 83rd AMS Annual Meeting, Long Beach, CA, February 9-13, 2003).

By running the PCM with each human climate forcing turned on in separate runs, and in combinations, the relative influences of the different forcings can be compared with respect to these metrics.

This approach addresses our hypothesis that LULC change (and also the diverse effects of aerosols and the biogeochemical effect of doubled CO2) have a greater effect on climate spatial patterns than that due to the radiative effect of a doubling of the well-mixed greenhouse gases. Since these forcings alter the spatial pattern of tropospheric diabatic heating, an analysis of this change, due to the different climate forcings, provides
a direct measure of how the pressure gradient field is altered. The pressure gradient field represents the fundamental dynamics that drive atmospheric circulations. With the PCM you have a excellent model to evaluate these issues by model sensitivity studies.�

Time will tell if these recommendations are considered.

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