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Farming, logging, development affect climate, tooNASA study finds 'human-caused land cover changes' key
By Richard Stenger (CNN)
(CNN) -- Cutting trees, building cities and growing crops have profound effects on the climate in addition to human activities that release greenhouse gases, a new NASA study reports. Land surface disturbances influence everything from temperature, precipitation, atmospheric circulation and how much solar heat bounces off the planet. Concentrated development, in particular in North America, Europe and Southeast Asia, disperses enough heat into the atmosphere to rival the effect of all greenhouse gas emissions combined, according to atmospheric scientists. "Our work suggests that the impacts of human-caused land cover changes on climate are at least as important, and quite possibly more important, than those of carbon dioxide," said Roger Pielke Sr. of Colorado State University in Fort Collins. Carbon dioxide is the primary culprit among numerous heat-trapping gases caused by human activity thought to contribute to global warming. "Through land cover changes over the last 300 years, we may have already altered the climate more than would occur associated with the ... effect of a doubling of carbon dioxide," Pielke said in a statement this week. If current trends continue, carbon dioxide concentrations in the atmosphere will double within 50 years. Scientists predict that the added greenhouse gases could push the global temperature up several degrees by the end of this century, causing major changes in regional weather patterns. Pielke and colleagues, who conducted the study for NASA's Earth Observing System Project Office and the National Science Foundation, said the type of land surface affects how it redistributes solar energy into the atmosphere. For instance, if farmers replace forests with crops, less water evaporates from leaves, which contributes to hotter temperatures in that area, they said. And in places with dwindling snow or ice cover, whether because of retreating glaciers or reforestation, the land reflects less sunlight and absorbs more heat, leading to hotter temperatures. The net effects are complex and sometimes seem contradictory. For example, compared with non-irrigated land, more water evaporates from irrigated fields, which cools and moistens the nearby air. Yet on a larger scale, atmospheric water vapor contributes greatly to greenhouse gas warming. The scientists propose a new method to predict climate change, which factors in how different kinds of land forms absorb, reflect or distribute heat.
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