This post will look at the semi-recent article by Feddema et.al. in Science, The Importance of Land-Cover Chance in Simulating Future Climates.

Abstract: Adding the effects of changes in land cover to the A2 and B1 transient climate simulations described in the Special Report on Emissions Scenarios (SRES) by the Intergovernmental Panel on Climate Change leads to significantly different regional climates in 2100 as compared with climates resulting from atmospheric SRES forcings alone. Agricultural expansion in the A2 scenario results in significant additional warming over the Amazon and cooling of the upper air column and nearby oceans. These and other influences on the Hadley and monsoon circulations affect extratropical climates. Agricultural expansion in the mid-latitudes produces cooling and decreases in the mean daily temperature range over many areas. The A2 scenario results in more significant change, often of opposite sign, than does the B1 scenario.

This study attempted to evaluate whether future land use decisions could alter the outcomes of two future IPCC climate simulations. I would bet that because it was published that it does provide at least a little insight to the problem. *wink*

As always with these modelling studies, I’m going to skip over the part where they describe their model. This is mostly because I find it boring, and that I don’t totally understand it. But I do find the results interesting, so I’ll discuss them here.

They find that land-cover changes do affect the regional temperatures. However, globally averaged temperature differences are very small because because the regional climate changes offset each other. This point is glossed over in the text, but it has significant repercussions. If projected land use change does not contribute significantly to the global temperature then global models that can accurately forecast regional temperatures is not important to forecasting an average global temperature. In essence, it’s unimportant if we can accurately forecast regionally because it is offset by a equally inaccurate regional forecast elsewhere.

One interesting finding was that the maximum temperature response in cells converted from tropical broadleaf evergreen forests to agriculture was minor. The minimum temperature change is generally what controlled the diurnal temperature range. Higher temperature as night have been shown to cause increased human stress.

In one scenario, the eastern equatorial Pacific shows a significant cooling which looks like a La Nina pattern. Thus for these conditions in the summer, we would expect to see wetter than normal conditions in the Pacific Northwest. The southern United States would be drier and warmer. Wintertime we’d expect a larger effect, with a cooling in the Southeast and a warming in the Northwest.

They conclude by stating that “results from this study suggest that the choices humans make about future land use could have a significant impact on regional and seasonal climates.”

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