Scientists agree that global warming really is occurring and will affect what you grow.

Farmers whose fortunes lie with the weather have one more factor to contend with in the future: global warming. A new report from the National Research Council (NRC) endorsed the concept that global warming is occurring.

NRC scientists found substantial evidence to show that the earth's atmosphere has warmed, despite conflicting temperature data. Some data show that surface air temperatures have warmed while middle atmospheric temperatures have not. But NRC's conclusion is that global warming is "undoubtedly real."

Regardless of what farmers think, they are inextricably tied to this event. A changing weather scheme will affect farming practices, and some of those practices may, in turn, slow the warming trend.

"If you have global warming, farmers will adjust," Bruce Babcock, director, Center for Agricultural and Rural Development (CARD), Ames, IA, reports. "It will take time. But economics will drive it. If Iowa is not a good place to grow corn, they won't grow corn."

Evidence of warming For years, scientists and environmentalists have claimed that emissions of heat-trapping industrial gases (called greenhouse gases) are warming the earth's atmosphere faster than would naturally occur without human pollution. Now evidence has accumulated in favor of the theory.

The evidence comes from many sources. The NRC scientists, for example, examined temperature data and computer simulations of temperature trends and concluded that the earth's surface temperature has risen 0.7 to 1.4 degrees F in the last 100 years.

"The rate of warming is much faster than observed in the last 1,000 years as interpreted from tree rings, lake sediments and ice cores," Gene Takle, Iowa State University climatologist, says. He explains that scientists reconstructed average temperatures over the past 1,000 years and found that the planet temperatures cooled a little over 900 years until 1900. Then temperatures abruptly rose.

The retreat of glaciers also indicates global warming. These large, stable bodies of ice are not affected by short-term weather events. Instead, warming over a long period of time will decrease their size, which is happening. Glacier National Park had more than 150 glaciers in 1850, but today, only 50 glaciers remain.

Other evidence of global warming lies in cases such as the outbreak of mosquito-carrying malaria in mountainous African villages. These villages had not been infected by malaria before, leading scientists to conclude that enough warming has taken place for mosquitoes to live.

Cool atmosphere "Just from this evidence, it seems the rate of change is beyond the range of natural variability," Takle says. But the issue was complicated in the 1950s to 1970s when global temperatures dropped slightly. "If greenhouse gases built up then, why would temperatures go down?" he asks. "The reason is due to a combination of sulfate aerosols and flickering of the sun." Sulfur dioxide emitted from coal-burning power plants condenses in the atmosphere and forms particles that reflect solar radiation. The result is a cooling effect in the atmosphere, Takle says.

Atmospheric cooling also can come from sunspots or flickers in the sun's brightness. "These are small, but still large enough to cause changes in our climate over decades," Takle explains. "So it is an awkward situation. If we do a better job of getting sulfur out of the atmosphere, we're going to contribute more to global warming."

Warmer nights If global warming continues, computer models project that by 2050 average daytime temperatures will be 2 to 3 degrees F warmer in the summer in the Midwest. Nighttime temperatures will go up even more, Takle says. Why? Warmer temperatures lead to more precipitation and cloudiness, which in turn keeps the nighttime air from cooling off.

"This may or may not be important for corn and soybeans," Takle says. "Perhaps more relevant is what about the change in variability? Will we expect more floods, droughts and extremes in temperatures? Those are perhaps more relevant but more difficult to answer."

The global warm-up already may be affecting where soybeans are planted. CARD's Babcock suggests that the increase in the number of soybean acres in the Red River Valley of North Dakota may be in part due to warmer temperatures.

"It might be evidence of global warming," he says. "Or it might be that breeders have been able to breed short-season soybeans or the government is paying farmers more to plant soybeans instead of wheat.

"You won't be able to draw a line in the sand and say this is the impact of global warming," he adds. "But if you look back after 20 years, then you might be able to figure it out."

Slowing the heat As the evidence mounts and computer models predict more warming, scientists are recommending action. "We need to look very seriously at ways to reduce the rise of carbon dioxide (a primary greenhouse gas) in the atmosphere," Takle states. One way is to stop burning fossil fuels, which will not occur, at least in the next couple decades.

Instead, some scientists believe a combination of reforestation and steps to reduce the greenhouse gases should work at a cost that is lower than the cost of limiting fuel use, Takle says.

Farmers will play a big role in this. Carbon sequestering in soils with minimum tillage will offset part of the production of carbon emissions. In addition, minimum tillage will reduce fuel use, cutting back further on emissions.

"This is quite a new issue," Takle says. "There are a lot of unresolved questions. So we will be learning more as time goes on. I think there will come a day when we can rebuild our soil carbon. We've burned about half of it out of our prairie soils in Iowa."

He also believes other conservation practices like wetlands and buffer strips along streams will become more attractive as the nation tries to slow the emission of greenhouse gases.

Controversial role The farmer's role in global warming has caught the eye of farm groups like the American Farm Bureau and American Corn Growers Association. These groups oppose a world plan, called the Kyoto Protocol, to lower greenhouse gas emissions. The plan calls for industrialized nations, including the U.S., to reduce the emission of greenhouse gases such as carbon dioxide over the next decade.

The farm organizations state that the protocol will place an unfair burden on U.S. farmers by causing fuel prices to skyrocket and farm profits to plummet. Congress has not signed the protocol.

CARD's Babcock disagrees that farmers will suffer needlessly from plans to reduce global warming. Instead, he believes farmers will adjust. If farmers face restrictions on fuel use or high prices, he says, "they won't go across the field so many times. They will probably do more no-till and gain carbon credits."

Weather forecasts As the focus on global warming and the weather continues, Iowa State University is working to help farmers anticipate the weather and use it to purchase crop inputs.

Three-month to two-year forecasts are improving in accuracy, Takle says. Crop modelers hope to put the forecasts into computer models to help farmers decide what seed to buy based on the forecasted weather conditions. The models will also help farmers determine chemical needs and timing for fieldwork.

"We're trying very hard to work with both the climate forecast centers and with farmers to bridge that gap," Takle says. "We want to be of some help to mitigate the impact of climate change."