Additional Evidence as to Why Land-Use/Land-Cover Change is a First-Order Climate Forcing

A September 13, 2005 NASA Press release entitled “Tropical Deforestation Affects Rainfall in the U.S. and Around the Globe” reports on recent research work led by Roni Avissar of Duke University that has provided further evidence of the importance of land-use/land-cover change as a first-order climate forcing. As the news release states

“Today, scientists estimate that between one-third and one-half of our planet’s land surfaces have been transformed by human development… Our study carried somewhat surprising results, showing that although the major impact of deforestation on precipitation is found in and near the deforested regions, it also has a strong influence on rainfall in the mid and even high latitudes,” said Roni Avissar, lead author of the study, published in the April 2005 issue of the Journal of Hydrometeorology… Deforestation does not appear to modify the global average of precipitation, but it changes precipitation patterns and distributions by affecting the amount of both sensible heat and that released into the atmosphere when water vapor condenses, called latent heat,” said Avissar. ‘Associated changes in air pressure distribution shift the typical global circulation patterns, sending storm systems off their typical paths.’ And, because of the Amazon’s location, any sort of weather hiccup from the area could signal serious changes for the rest of the world like droughts and severe storms.”

This work is discussed in detail in Avissar et al. 2005.

This new research supports the conclusions summarized in the NASA publication entitled Local or Global Problem? . As reported in that publication with respect to the global climate implications of land-use/land-cover change,

“Though their results drew national media attention from many sources, all the scientists involved in the research agree that the scientific arena is where the results should be evaluated. Pielke hopes these results will convince scientists to give the land cover-climate connection more attention. In the past, he has been frustrated by the lack of attention to the topic.

Gordon Bonan is a climate modeler for the National Center for Atmospheric Research in Boulder, Colorado. `It’s definitely true that historically, the emphasis in global climate change research has been on other climate forcings-greenhouses gases, solar variability, aerosols-and that the role of land cover has been neglected. Roger’s work, his persistence, has really played a large role in bringing people around to the importance of it.’ Bonan thinks people are finally beginning to listen.

So far, what research has been done on the global-scale influence of land cover change on climate seems to suggest it plays a minor role. That’s not surprising, says Bonan, considering how small the Earth’s land surface is compared to its oceans and that our most common metric for climate change is global mean temperature. Even significant changes in the temperature where we live can get ‘washed out’ (at least for a while) in the global average of a world mostly covered by oceans.

‘Nobody experiences the effect of a half a degree increase in global mean temperature,’ Bonan says. ‘What we experience are the changes in the climate in the place where we live, and those changes might be large. Land cover change is as big an influence on regional and local climate and weather as doubled atmospheric carbon dioxide-perhaps even bigger.’ That’s the idea Pielke says he has been trying to get across for years. ‘Climate change is about more than a change in global temperature,’ he says. ‘It’s about changes in weather patterns across the Earth.’ Even if it turns out that land cover change doesn’t significantly alter the globally-averaged surface temperature of the Earth, it’s still critically important. ‘The land is where we live. This research shows that the land itself exerts a first order [primary] influence on the climate we experience.’

The full text of this May 17 2005 NASA publication article is available at the link above.

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