Everyone knows that draining a wetland is bad for the animals that live there. But research shows that the practice also changes the local weather. You'll hear why in this Science Update.
How farms cause freezes in Florida. I'm Bob Hirshon and this is Science Update.
In Florida, a bout of frigid weather can cost orange growers their entire crop. That's why over the last century, farmers spread farther south in hopes of escaping these damaging freezes.
But a study in the journal Nature shows that turning wetlands into cropland has contributed to the very problem it was trying to avoid. Curtis Marshall, a Ph.D. candidate in atmospheric science at Colorado State University, modeled a freeze event on a computer—comparing Florida as it was a century ago to the present day.
The difference that you see that emerges from the model simulations is due solely to the difference in the land surface. And in one case with cropland, the temperatures fell below freezing and were below freezing for a longer period of time than if natural wetlands were present in those computer simulations.
Roger Pielke, a Colorado State professor and co-author of the study, says wetlands act as buffers against these freezes.
They basically provide a storage of heat, and they also evaporate and transpire water into the atmosphere that prevents the temperature from falling as low at night.
The researchers say that the work provides another example of how human changes to the landscape can in turn change the climate. I'm Bob Hirshon for AAAS, The Science Society.
Making Sense of the Research
Wetlands—a name given to swampy or marshy environments like Florida's Everglades—are among the most threatened ecosystems in North America. That's because they're very inconvenient for humans. You can't build on them, you can't drive on them, and even though they're wet, they're too mucky for swimming. Plus, they tend to breed mosquitoes and other biting insects. It's no wonder wetlands have often been considered "wasted space" by human settlers and developers, and why many of them have been drained or filled with dirt to make the land more "useful."
Of course, the altering of wetlands has been devastating to thousands of species that make their homes there, especially birds. But in this case, the destruction of wetlands in Florida has come back to haunt its human perpetrators. In fact, it creates a cycle of destruction: in order to escape the cold, farmers move their orange crops southward, which requires them to drain wetlands, which makes the climate colder, which in turn makes the farmers move even farther south. If it weren't for the Atlantic Ocean, the pattern might just keep going all the way to the Equator.
How do wetlands protect an area from freezing? As Pielke explains, the water in the wetlands traps heat during the day, and then releases it into the air at night along with moisture. That's why coastal areas are usually milder in the winter than areas further inland: the water moderates the temperature of the air.
In the case of Florida wetlands, the moderating effect is just enough to raise the temperature by a few degrees. But if overnight low temperatures are already hovering near the freezing point, losing those few degrees can lead to dozens of damaging frosts that wouldn't have occurred otherwise. That's what happened after farmers converted the southern wetlands into drier cropland.
Now that they know this is happening, weather forecasters might be able to better predict freezes that have taken the orange farmers by surprise in the last several years. That could mean fewer crop losses for farmers who respond to the freeze warnings. But it doesn't erase the wide variety of other problems, known and unknown, that the disappearance of the wetlands has set in motion.
Now try and answer these questions:
- What are some of the reasons wetlands are endangered?
- How has the loss of wetlands in Florida affected the orange industry?
- Given the information in this article, what other kinds of environmental change do you think might lead to changes in local climate? Give reasons for your answer.
- In a case like this, how do you balance the demands of an industry (and, by extension, the demands of the American consumer) and the sensitivities of the environment? If you were writing laws that governed the conversion of wilderness to farmland, what restrictions would you put in place? Would these restrictions be practical? What would be some of the less desirable effects of your regulations?
The Environmental Protection Agency's Wetlands page has information about what wetlands are, how they function in the environment, and how they are protected under the law.
The University of Florida's Howard T. Odum Center for Wetlands has wetlands information, links, and photos about Florida's wetland ecosystems.