Study gives clearer picture of how land-use changes affect U.S. climate


WEST LAFAYETTE, Ind. — If you want to talk climate change, consider this: Greener land cover contributes to cooler temperatures, and almost any other change leads to warmer temperatures.

That was the finding of researchers at Purdue University and the universities of Colorado and Maryland, whose paper is set to appear in the International Journal of Climatology later this year.

Quite simply, says the lead author Purdue doctoral student Souleymane Fall, land use should be better incorporated into computer models projecting future climate conditions.

Not often considered

Dev Niyogi, a Purdue earth and atmospheric sciences and agronomy professor, and the Indiana state climatologist, said the study highlights a significant trend, particularly the warming trend in terms of temperatures, which is explained by the land-use change. He is the study’s corresponding author.

Niyogi and Fall say the idea that land use helps drive climate change has been poorly understood compared to factors such as greenhouse gas emissions. But that is changing.

“People realize that land use cover also is an important force and not only at the local but also at the regional scale,” said Fall.

The researchers used higher resolution temperature data than previous studies, meaning the data was more detailed, Niyogi said. They also employed dynamic data on land-use changes from 1992-2001, which was derived from satellite imagery.

Study findings

Among the study’s findings:

• In general, the greener the land cover, the cooler is surface temperature.

• Conversion to agriculture results in cooling, while conversion from agriculture generally results in warming.

• Deforestation generally results in warming, with the exception of a shift from forest to agriculture. No clear picture emerged from the impact of planting or seeding new forests.

• Urbanization and conversion to bare soils have the largest warming impacts.

Land use

In general, land use conversion often results in more warming than cooling.

The researchers were able to separate the effects of land use or cover from greenhouse warming and isolate the impact from each land use or cover type. The more detailed data provided a clearer picture of the effects of land surface properties on near-surface temperature trends.

While the effects of greenhouses gases like carbon dioxide are clear, University of Maryland professor Eugenia Kalnay said, the study does suggest land use needs to be considered carefully as well.

“I think that greenhouse warming is incredibly important, but land use should not be neglected,” she said. “It contributes to warming, especially in urban and desertic areas.”

Another study co-author, Roger Pielke Sr., said the results indicate that “unless these landscape effects are properly considered, the role of greenhouse warming in increasing surface temperatures will be significantly overstated.”

Pielke is a senior research scientist in atmospheric and oceanic sciences at the Cooperative Institute for Research in Environmental Sciences and the Department of Atmospheric and Oceanic Sciences at the University of Colorado in Boulder.

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