Bill chill florida as farms replace wetlands
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Posted on Thu, Nov. 06, 2003
Study discovers a big chill as farms replace wetlands
Replacing wetlands with farm fields has worsened the effects of freezes in South Florida, a study that appears in the journal Nature suggests.
BY CURTIS MORGAN
Over the last century in Florida, farmers have moved south to escape damaging freezes, but ironically, in the process of plowing under marshes, they may have brought some of the chill with them.
Draining portions of the Everglades and Kissimmee River Basin removed a natural source of warmth and may have created larger, longer cold snaps around Lake Okeechobee, heart of the state's sugar and winter vegetable crop, according to an article published today in the journal Nature.
The intent was to study climate impacts on the agricultural industry and to show that humans can alter the climate in more ways than just producing pollution from smokestacks and car exhausts, said Roger Pielke Sr., a professor of atmospheric sciences at Colorado State University who co-authored the study.
''A lot of the focus of climate change has been on carbon dioxide and greenhouse gases,'' Pielke said. ``This suggests that land-use changes are a major player in climate changes.''
Farmers shrugged their shoulders at the findings.
''It's not surprising at all,'' said David Kaplan, owner of Plant Doctor Nursery and former president of the Dade County Farm Bureau.
Kaplan said every farmer knows that water holds warmth. ``People flood groves when it gets cold.''
Phil Leary, director of governmental affairs and environmental point person for the Florida Farm Bureau, said nearly all of the land was drained by the government to attract farmers decades before anyone was worried about global warming or climate change.
And, he argued, the alternatives have even bigger impacts.
''If you think agriculture is bad for the environment, asphalt and concrete is much worse,'' he said.
The study, by Pielke, graduate student Curtis Marshall and Louis Steyaert of the U.S. Geological Survey, was based on computer modeling that compared climate conditions in pre-1900s South Florida with data recorded during a 1997 freeze.
That surprise freeze, according to the study, resulted in more than $300 million in losses for sugar and vegetable growers in regions that had once been wetlands.
That wetlands provide natural warmth isn't a new idea, the researchers said.
Water retains heat long after air temperatures drop, which is why farmers routinely irrigate crops during cold snaps. The water is warm but even a coating of ice can form a protective outer shield during extreme freezes. Marshes also produce a great deal of evaporation, which warms the air and traps heat that would otherwise radiate from the ground.
But their study, said Pielke, confirms anecdotal evidence and assesses the actual temperature difference on the ground.
What the computer found was that temperatures in unspoiled wetlands -- particularly in the densely farmed area southwest of Lake Okeechobee -- would have remained above freezing level. In other areas, the chill might have been several degrees less severe and lasted for a shorter period.
The researchers said they found similar results analyzing freezes in 1983 and 1989.
The U.S. Sugar Corp., a major grower of sugar and citrus in the region, declined to comment.
Spokeswoman Judy Sanchez said the company wanted to examine the full study, not a synopsis published in Nature.
But the farm bureau's Leary questioned the data. The sugar industry, for one thing, holds vast amounts of water in canals, he said.
The state also suffered serious droughts during the freezes the study analyzed, which would have affected both natural and cultivated areas, he said.
''If the wetlands weren't full of water, it wouldn't have mattered,'' he said.
Pielke said the study should help farmers plan for freezes but also underlines the importance that the Everglades and other wetlands play in the state's weather.
In another study published in July in Monthly Weather Review, another journal, the researchers found that urban and suburban development also had altered weather patterns -- making summers hotter and drier, an alarming ripple effect in a state worried about water shortages.
''That certainly gives more relevance for trying to restore the Everglades,'' Pielke said.