Model shows how Amazon land use may change Southwest U.S. climate
Jim Erickson, Rocky Mountain News
Published December 9, 2005 at midnight
In the coming decades, continued deforestation of Amazon jungles could strengthen the summer monsoon in the Southwest U.S. - including southwest Colorado - and offset some of global warming's effects.
That's one of the surprising results of a computerized climate study by researchers at the National Center for Atmospheric Research in Boulder.
The study's authors say it is the first to incorporate land-cover changes - caused by agriculture, deforestation and other human activities - in climate simulations using advanced global computer models.
"Land cover has long been one of those issues that really hasn't been included, because it's much more difficult to incorporate," said University of Kansas researcher Johannes Feddema, lead author of the study published in today's edition of the journal Science.
Feddema worked on the project while on sabbatical at the Boulder center. Six NCAR researchers are co-authors.
The enhanced Southwest monsoon is one example of what climate researchers call teleconnections: A change in one part of the world can have unanticipated effects on the climate thousands of miles away.
Each year, about 50,000 square miles of forest - an area about half the size of Colorado - is cleared worldwide, according to the United Nations Food and Agriculture Organization. Between 2000 and 2005, South America suffered the greatest losses, largely because of conversion of forest to pasture and farmland.
If significant Amazon deforestation continues in coming decades, tropical air-circulation patterns will shift, allowing summer moisture to drift farther north and be captured by the Southwest U.S. monsoon, according to the study.
As a result, southwest Colorado could see an extra 2 inches or so of annual precipitation - mostly in the summer - and summer temperatures could cool by a couple of degrees Fahrenheit by 2100.
Those changes could help offset anticipated warming because of the buildup of heat-trapping "greenhouse" gases from automobile tailpipes and smokestacks.
A recent study led by NCAR's Gerald Meehl suggests that Colorado can expect a temperature increase of 3.6 to 7.2 degrees Fahrenheit by 2100.
But Feddema stressed that there is "still a lot of uncertainty" in the land-use models and that today's Science paper is just a first step. The study does not account for the effects of urbanization or irrigated agriculture, for example.
And overall, regional climate variations resulting from land-use changes tend to cancel out each other, resulting in little change to the global average temperature.
"Compared to global warming, land use is a relatively small influence," Feddema said. "However, there are regions where it's really important."
A main point of the study is that climate modelers need to pay more attention to land-use changes in their simulations of 21st-century climate, he said.
That's a position Colorado State Climatologist Roger Pielke Sr. has held for several years.
In a commentary accompanying the Science report, Pielke chides the Intergovernmental Panel on Climate Change, the main international body that assesses climate- change research, for failing to adequately address land-use change.
The panel, "which has yet to appreciate the significance of the full range of phenomena that drive climate change, risks rapidly falling behind the evolving science if this effect is not included," Pielke wrote.
ericksonj@RockyMountainNews.com or 303-892-5129
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