Development & Aid, Environment, Headlines

AGRICULTURE: Rising Temperatures Chill Rice Production

Katherine Stapp

NEW YORK, Jul 13 2004 (IPS) - Climate change is having even more dire consequences on food production than previously thought, say researchers who found that a temperature increase of a single degree Celsius lowers rice yields by at least 10 percent.

The study, co-funded by the International Rice Research Institute (IRRI) and the University of Nebraska, analysed weather data gathered at IRRI’s model farm in the Philippines from 1979 to 2003, and compared it with yields from the last 12 rice harvests.

While previous studies have linked warmer temperatures with falling agricultural output, most have underestimated the full consequences, scientists say.

"What’s most significant is that this is the first report with actual field data linked to real climate data proving that small increases in temperature can have a high impact on yield," said Kenneth Cassman, a lead U.S. researcher in the project.

"Our research shows that consistent with theories about the greenhouse effect, the increase was three times as great at night as during the day," he added in an interview.

During the period studied by the team, mean temperatures at the farm increased by 0.35 degrees Celsius during the day, but by 1.13 degrees at night. That forced the plants to work harder to shed excess heat, Cassman explained, resulting in stunted growth.

"Other studies have been based on indirect approaches, like simulation modelling," he added. "This is a validation of those studies, but it also demonstrates that the models used are not sensitive to the differential impact of night versus day temperatures."

The implications for global food security are extremely worrisome, experts note, because rice feeds half the world’s people, and provides the livelihoods of a billion more.

Even as demand for rice is expected to jump about 40 percent in the next two decades, production has become sluggish, and is now growing just one percent annually. Experts warn that new demand will have to be met with less land, less water, less labour and fewer chemicals.

"Rice is the most important human food crop because it provides more calories than any other," Cassman said. "The challenge of meeting the needs of an increasing population without expanding farming areas, in the context of this new challenge (of global warming), is major."

Over the last 100 years, the earth’s temperature climbed on average by about half a degree, due at least in part to human activity and the build-up of carbon dioxide (CO2) in the atmosphere. Estimated warming for the next century is predicted at 1.5 to 4.5 degrees – meaning rice crops could dwindle by 10 to 40 percent.

Other studies have shown that gradual increases in temperature cause significant decreases in productivity – up to 17 percent – for other important crops like corn and soybeans.

Corn feeds hundreds of millions of people, particularly in the developing world, where it is a staple nutrient as well as livestock feed.

Africa is one of the regions hardest hit by global warming, suffering heavier rainfall in some areas and desertification in others. In the giant catchment basins of Niger, Lake Chad and Senegal, total available water has decreased 40-60 percent.

The U.N. Environment Programme (UNEP) warns that "lack of rain, warmer temperatures and increases in evaporation could reduce yields by a third or more in these areas."

Global warming also affects crops by allowing northward expansion of crop diseases. In the United States, recent massive outbreaks of wheat stripe rust, soybean sudden death syndrome and various viral diseases, blamed on climate changes, cost farmers billions of dollars.

In Europe, shifts in agricultural output last year mirrored predictions by soil scientists that the southern countries would suffer shrinking harvests, due to heat waves and drought, while the north would gain from boosted yields thanks to milder weather.

Some researchers believe the answer lies in adapting agriculture to the realities of climate change, and are introducing drought-resistant strains of maize that produce up to 35 percent more grain than current varieties.

Others stress that the problem cannot be solved without addressing the root causes of global warming – namely, CO2 emissions from cars and factories.

"It’s like being an alcoholic: the first step is in admitting that you have a problem," Cassman said. "I don’t think we’re doing nearly enough to address this issue."

Some scientists fear that it may already be too late.

"For small subsistence farmers in Asia, where rice agriculture is so important, there will be little that can be done to overcome increases in temperature," said Greg Asner of the Department of Global Ecology at Carnegie Institution in Stanford, California.

"Our climate is changing, and these changes are, to some extent, unavoidable at this point. Too little has been done to avert the climatic changes that society will experience in the coming decades," said Asner, who recently published a study in ‘Science’ magazine showing that even in highly mechanised and managed wheat and corn agricultural systems in the United States, crop yields succumb to higher temperatures.

"Movement of agricultural operations to cooler regions – for example, northward in the northern hemisphere – may be a partial solution for some crop types (like) wheat and corn, in some regions such as North America."

But, he added, "this may not be possible in Southeast Asia, especially for the millions of small land holders that subsist on rice today."

Experts working on food security also warn that a northward shift – which has already been happening for decades – would likely aggravate the problem further.

"It simply moves control out of the hands of farmers and into the hands of giant food-producing enterprises," said Kathy McAfee, the executive director of Food First, a non-profit think tank that works on solutions to hunger and poverty.

"Even if more food were produced as a result, there would be more hunger because you’re speeding up the problems we already have, like people losing their land and their traditional knowledge."

"Obviously, we need a strong, enforceable pact to reduce, not just stabilise, greenhouse gases," she told IPS. "But the only way to increase food production is through farmer-centred agro-ecological research that is cooperative and linked to social policies that retain or increase local people’s control over land and water resources."