The Why Files The Why Files --

Earth Day 2006: Checkup reveals global fever


Pay dirt
Global warming started as a problem in the sky: we burn trees and fossil fuels, and make carbon dioxide that re-radiates heat back toward earth, which warms the atmosphere. But as global warming science matured, Amount of ice covering the Arctic has dramatically shrunk between 1979 and started looking at the ocean and the continents. The interactions grew vastly more complicated, but the projections also got more realistic.

Between 1979 and 2003, Arctic perennial sea ice has been decreasing at a rate of 9 percent per decade. The animation at right shows the minimum sea ice concentration for the year 1979, and then the minimum sea ice concentration in 2003. Original photos from NASA

The biggest change in the landscape is caused by agriculture, says Jonathan Foley, director of the Center for Sustainability and the Global Environment at the University of Wisconsin-Madison. To feed 6.5 billion people, we've created of 18 million square kilometers of cropland, about the area of South America. To feed our cows, we have created almost twice as much rangeland -- 34 million square kilometers -- about the area of Africa. "For cows, we have created the world's largest ecosystem," Foley told AAAS.

Agriculture, he says, "is far and away the single biggest transformation of the biosphere since the last ice age." Once you add urban areas, he said, "About 40 percent of the land surface, excluding Antarctica and Greenland, is completely cleared and turned into something else."Agriculture is by far the single biggest transformation of the biosphere since the last ice age. How is that changing the planet?

Farming and ranching are necessary, but they do change everything, replacing native ecosystems for bare dirt, grasses and crops that are lovingly tended to make food for 6.5 billion hungry mouths.

Foley says deforestation may be doing far more than reducing biodiversity and rainfall. It could also be promoting malaria, a dreaded blood parasite that afflicts half a billion people around the world each year, and kills 1 to 3 million. Research by Jonathan Patz, associate professor of population health science at the University of Wisconsin-Madison, has found a 300-fold (NOT 300 percent) increase in the chance of being bitten by Anopheles darlingii, a malaria-carrying mosquito, when just 20 percent of the tropical rainforest in Peru was destroyed.

"That's preliminary data, but it's kind of extraordinary," Foley says. "We are not sure why this is, but we know the mosquitoes are much more abundant if you have sunlit pools of water." The cause could be a change in water temperature or acidity, or the absence of predators, but the result could explain the epidemic of malaria in settlements around new deforestation.

In the dead zone
The Gulf of Mexico offers another example of the long-distance effects of changing the landscape. Through the Mississippi River, the Gulf receives a slug of fertilizer from farm fields across 41 percent of the lower 48 states. The fertilizer stimulates ocean plant growth and when the plants decompose, they sap oxygen in the water. This de-oxygenation has caused the 18,000 square-kilometer " dead zone" in the Gulf. Fish cannot live in this section of the nation's most important coastal fishery.

Green tractor pull large pill-shaped tank of chemical fertilizer across brown untilled field Fertilizer can run off farmland, drift downriver, and harm fish in the sea. Photo: USDA

Similar low-oxygen zones occur near the discharges of many major rivers that drain farming regions, says Foley, including the U.S. Atlantic Coast, the Black Sea, North Sea and Yellow Sea.

The point is not to blame farmers for over-fertilizing, but to build incentives for sensible use, Foley says. Farmers in the Mississippi basin are now using 30 times more nitrogen fertilizer than 40 years ago, he adds. "A lot of farmers use far more fertilizer than is recommended by the USDA (U.S. Department of Agriculture]. Fertilizer is cheap, but because nobody is paying directly for the pollution this causes, there is an incentive to use more of it." Farmers are usually pressed for cash, he adds. "It's hard to blame those guys, but if we turned around the subsidy structure, there might be an advantage in using less fertilizer. This is more of an economic question than a scientific one."

Getting ethical
The future of a warming world looks bleak, says Foley. After only 0.6 degrees C of warming, we are already seeing major changes in plants, animals, rainfall, ice and sea level. Even the few skeptics of 10 years ago are now silent, and the scientific position is unanimous: "It's pretty much nailed... . You can't read a paper without reading another piece of evidence for global warming. At the edges, there are a few questions, but the scientific score is 1,000 to 0. This is not a big bunch of hooey."

Time magazine has just run a frightening cover story: "The climate is crashing, and global warming is to blame. Why did the crisis hit so soon--and what we can do about it".

Different areas of the Arctic Ocean melt at different rates, creating confusion among researchers.Global warming is causing ice to melt fast in the Arctic Ocean. In June 2005, the end of the first month of the melt season, ice is melting abnormally fast in the red areas, unusually slow in the blue areas. The black line shows the median ice edge for 1979 through 2000. The sea ice was at record low in June, 2005: 6 percent below the long-term average. Courtesy Ken Knowles and Terry Haran, National Snow and Ice Data Center.

What we have seen regarding climate change is bad enough, Foley says, but it's only a taste of what is to come. Have we mentioned feedback? Warming is already melting the Arctic Ocean, and since water is darker than ice, it will absorb more solar radiation, which will cause more warming.

A warming climate may also release methane -- a powerful greenhouse gas -- from permafrost and possibly under the continental shelf. The subject is uncertain, but massive additions of methane to the atmosphere could throw existing predictions of warming out the window. Overall, says Foley, the scenarios of the Intergovernmental Panel on Climate Change "are actually conservative," because they do not include some "nasty feedbacks."

Another source of concern is the "flywheel effect"-- the way that warming follows increases in greenhouse gases. "There's a fundamental problem," says Foley. "The climate change we are seeing right now is really only catching up to the CO2 emitted by the early 1960s. There is a huge delay in the system. It takes a few decades for the earth's temperature to come into equilibrium." (In fact, the recent British study of ice at Dome C in the Antarctic found that carbon dioxide levels peaked centuries before atmospheric temperatures did). "So even if we turned off fossil fuels tomorrow, which we won't, there is a lot more global warming built into the system, at least over the next few decades."

A graph shows sharply spiking levels of carbon dioxide in the last 20 years.
Levels of several important greenhouse gases have increased by about 25 percent since large-scale industrialization began around 150 years ago. For 20 years, about three-quarters of human-made carbon dioxide emissions has come from burning fossil fuels. Graph: U.S. Department of Energy

To Foley, this degree of global change looks less like a scientific problem than an ethical conundrum. "It is the challenge of our time, it's multigenerational, and is one of the most pressing ethical problems of human history. Do we have the right to doom other societies for us to drive our SUV to the mall?"

Due to the flywheel effect, the likely feedback mechanisms, and the fact that carbon dioxide lingers in the atmosphere for about a century, Foley is one of many scientists who believe a warming of 1 degree; to 2 degrees; C is practically inevitable. The question he asks, is this: How much warming are we willing to risk? What actions should we take now to slow, and even stop, the production of greenhouse gases?

"When you have these delays in the system, when there is so much inertia, it's like driving an 18-wheeler toward the edge of a cliff," Foley says. "We should stop now, but we have only lightened the foot on the accelerator with the Kyoto agreement. We need to be slamming on the brakes now, and hoping we won't go over the cliff."

Grim global reading ahead.


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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