When Andy Jarvis wants to explain to locals how future climate change will affect agriculture in the tropics, he uses a familiar landmark: a mountain.

A 2-degree-Celsius increase in temperature -- the anticipated rise from climate change in the next 40 years -- is roughly equivalent to a 500-meter change in elevation, he said. Farmers growing at an elevation of 1,500 meters will need to move crops up to 2,000 meters.

"The reality of that to people is tremendous," said Jarvis, a researcher with the Decision and Policy Analysis program of the International Center for Tropical Agriculture (CIAT) and a team leader with the CGIAR Research Program on Climate Change, Agriculture and Food Security. To many South American or African farmers, "everything that is coffee today will not be coffee tomorrow."

To farmers in tropical regions, climate change has become a tangible reality. CIAT researchers have already found that increasingly erratic weather and high temperatures will change the growing patterns of world commodities like chocolate and coffee. But it will also affect cassava, millet and other crops vital to local populations.

Scientists sometimes struggle to match the tangible evidence of today with the theoretical climate models for the next 50 or 100 years. Earlier this week, scientists Richard Washington of the University of Oxford in the United Kingdom and Mark New of the University of Cape Town in South Africa released studies on West Africa, East Africa and the Indo-Gangetic Plain of South Asia. These studies matched some of the most widely used climate models with projections for future agricultural output.

Instead of providing a nice, neat and clear answer, the findings showed that the effect of future climate change on agriculture is wildly uncertain. While the trends associated with climate change -- hotter days, heavier rainfall and a greater number of extreme weather events -- are present in the models, for many crops in Africa and Asia it's not clear how extensive the effects will be.

This uncertainty is not necessarily a bad thing, but it makes climate science -- especially in relation to a field as vital as agriculture -- difficult to grasp. New, who conducted the study of climate models in the Indo-Gangetic Plain, said it would be problematic to rule out the "less bad" models from the worse ones.

"It's safer to ... be looking at the full range of uncertainty in the models rather than picking and choosing," he said.

Dealing with the unknown
The "U word," as Jarvis calls it, is an uncomfortable one for those who don't work with it daily. Yet it is something that ordinary citizens deal with daily without knowing.

"The reports are being completely open and honest about uncertainty," said Jarvis. Although daunting in the context of climate change, most people have learned to use weather forecasts to make decisions for everyday life.

"You can come up with hundreds of decisions," said Jarvis. "It's always built on partial information."

In general, African crops like banana, cassava, pigeon pea and rice respond well to high temperatures, and the areas of optimal growth for those crops could expand. Corn, millet, potato, sorghum, sweet potato and wheat have a lower temperature threshold for success, and yields are likely to diminish as temperatures rise. In South Asia, water availability and rainfall seem to be more limiting factors than heat for corn, wheat and rice.

On the ground, the effects already exist. A 2-degree temperature increase in Peru would limit the potato plant's ability to produce tubers, the edible root of the plant, said Jarvis.

Another root plant, cassava, is a staple crop in West Africa. Its future is also uncertain. While the study released by Washington shows that it will be one of the most resilient crops in the face of climate change, Claude Fauquet, director of the International Laboratory for Tropical Agricultural Biotechnology at the Donald Danforth Plant Science Center, believes that drier temperatures in West Africa will hurt yields, but cassava will see more productivity in central and southern Africa. CIAT is currently studying the crop's viability.

Fauquet said cassava is most likely to perish from the increase in pests and pathogens linked to warmer and wetter conditions. Mealybugs in Thailand and white flies in Africa are significant threats, with the latter serving as a vector for plant viruses.

"There will be a lot of outbreaks of diseases associated with climatic changes," he said, "in every part of the globe, for every crop."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500