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Fifty Years of Temperature Change in California, USA
LaDochy, S., Medina, R. and Patzert, W. 2007. Recent California climate variability: spatial and temporal patterns in temperature trends. Climate Research 33: 159-169.

The authors report that "when speculating on how global warming would impact the state [of California], climate change models and assessments often assume that the influence would be uniform (Hansen et al., 1998; Hayhoe et al., 2004; Leung et al., 2004)."

What was done
To assess the validity of this assumption, LaDochy et al. "use temperature trends in California climate records over the last 50 years [1950-2000] to measure the extent of warming in the various sub-regions of the state." Then, "by looking at human-induced changes to the landscape, [they] attempt to evaluate the importance of these changes with regard to temperature trends, and determine their significance in comparison to those caused by changes in atmospheric composition," such as atmospheric CO2 concentration.

What was learned
The three researchers found that "most regions showed a stronger increase in minimum temperatures than with mean and maximum temperatures," and that "areas of intensive urbanization showed the largest positive trends, while rural, non-agricultural regions showed the least warming." In fact, they report that the Northeast Interior Basins of the state actually experienced cooling. Large urban sites, on the other hand, exhibited rates of warming "over twice those for the state, for the mean maximum temperatures, and over five times the state's mean rate for the minimum temperature."

What it means
LaDochy et al. write that "if we assume that global warming affects all regions of the state, then the small increases seen in rural stations can be an estimate of this general warming pattern over land," which implies that "larger increases," such as those found in areas of intensive urbanization, "must then be due to local or regional surface changes."

Hansen, J., Sato, M., Glascoe, J. and Ruedy, R. 1998. A commonsense climatic index: Is climate change noticeable? Proceedings of the National Academy of Sciences USA 95: 4113-4120.

Hayhoe, K., Cayan, D., Field, C.B., Frumhoff, P.C. et al. 2004. Emissions, pathways, climate change, and impacts on California. Proceedings of the National Academy of Sciences USA 101: 12,422-12,427.

Leung, L.R., Qian, Y., Bian, X., Washington, W.M., Han, J. and Roads, J.O. 2004. Mid-century ensemble regional climate change scenarios for the western United States. Climatic Change 62: 75-113.

Reviewed 28 November 2007