WEST LAFAYETTE, Ind. — Global warming and its potential effect on agriculture has been a topic of debate for some time, and several studies attempt to predict the consequences of a rise in temperature by using computer models.

Now a report by researchers at Purdue and North Carolina universities suggests that studying higher temperatures alone is not an accurate way to measure the impact of climate change on agriculture. Instead, the researchers have studied the interchange of several climate-change variables, like temperature, radiation and precipitation, and how land use impacts the weather.

They found that drought - one possible outcome of rising temperatures - is the biggest threat to crop yields of the future.

“The bottom line is that if we only consider one variable, like increasing temperature, we come up with unrealistic estimates, or so called doomsday predictions,” said Dev Niyogi, an agronomy, and earth and atmospheric sciences assistant professor at Purdue and Indiana state climatologist, who co-authored the study.

“The message we want to highlight is that increased temperatures are not the main issue. It’s the associated feedback that is our main concern.”

For example, rising temperatures could cause the crops to grow taller, which would increase the evaporation and cloud formation. More clouds could change the radiation and impact the crops’ photosynthesis, and lead to more rainfall, which in turn could change soil moisture and temperature.

Understanding these interactions and being prepared for climate change will be key for the research community as well as the farmers on the ground, according to Niyogi. He said attitudes toward water and water quality should be reconsidered.

“I’ve been in parts of the world where 24-hour running water is a rare commodity. It’s not like that in the U.S., but we can’t take our water for granted.”

The research team tested 25 different climate scenarios on corn and soybean plots in North Carolina and compared the results with data from 1998, a year when the weather in the area was considered normal.

By changing multiple variables simultaneously they tried to replicate real weather scenarios. The scientists found that precipitation had the most impact on crop yields, whereas temperature and radiation changes had a less prominent, non-linear effect.

Niyogi said it’s also important to understand how urban sprawl and the ever-growing population’s insatiable appetite for fossil fuels will affect agricultural productivity.

“As a community, we need to understand land use as a driver for climate change. If the precipitation in Indianapolis changes, that will be more important to the surrounding counties than if the temperature changes,” he said. “If the Midwest gets excited about biofuels, the stakes are going to be higher and integrated assessments like these will become more critical.”

Although the study concluded that more research is needed on a regional level, Niyogi said U.S. communities need to act now to develop drought response and resource management plans.

“The issue of climate change is not for one individual or one government to address. It’s much more embedded within the fiber of community and it needs a community response,” he said, noting that other countries have successfully implemented such disaster-preparedness plans.

Research, education and continued monitoring of the weather are some of the tools that could be used, and Niyogi mentioned CoCoRaHS (Community Collabrative Rain, Hail and Snow Network), a grassroots volunteer network of weather enthusiasts who report precipitation in their local communities, as one way of improving our understanding of and refining our predictions for the climate. Indiana is already a member of this network and Illinois will join on Dec. 1.

Farmers can also help by working closely with their local extension agents.

“The users on the ground have the best feel for what kind of information they need. We’re struggling with a big interface issue, and we need to know what would be of most use to (the farmers).”

This farm news was published in the Nov. 22, 2006 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.