NASA confirms role of land use in climate change

by William Yeatman on March 30, 2004

Using the NASA Ecosystem Demography model to trace the evolution of vegetation distribution in the US over the past 300 years, researchers at Princeton University have confirmed that land use changes have significantly affected the US climate.

According to the NASA press release, “The researchers found land cover changes produced a significant cooling effect of more than one degree Fahrenheit in parts of the Great Plains and Midwest as agriculture expanded and replaced grasslands. Farmlands tend to create lower temperatures through increased evaporation. A warming effect was found along the Atlantic coast where croplands replaced forests.

“Compared to forests, croplands are less efficient in transpiration; a daytime process where water evaporates from leaves during photosynthesis and cools the air. A slight warming effect was also observed across the Southwest, where woodlands replaced some deserts.

“The study found land cover changes could impact local precipitation, but not as significantly as they affect temperature. The relatively strong cooling over the central U.S. has probably weakened the temperature difference between land and the Gulf of Mexico, slowing the northern movement of weather systems and resulting in enhanced rainfall across Texas. Consequently, the air masses reaching the Central Lowlands region, including Illinois and Indiana, are drier, causing rainfall reductions.”

Lead researcher N. J. Roy said, “It is important to understand the effects of changing land cover, because it can mitigate or exacerbate greenhouse warming. In the U.S. over the past 100 years, it seems to be offsetting greenhouse warming. The opposite is probably true in most other parts of the world. This finding has also been supported in previous research.”

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