Sugarcane – a principal crop for biofuel – reduces the local air temperature compared to pasturelands or fields growing soybeans or maize, according to a new study from researchers at Stanford University and the Carnegie Institution for Science. But sugarcane's effect on temperature is a "double-edged machete," as it increases ambient temperatures compared with natural vegetation.

These small local changes should be taken into consideration in studies of global climate change, the researchers said.

The researchers looked at changes in vegetation in the Brazilian Cerrado – a vast tropical savanna lying south of the Amazon basin – largeareas of which have been converted from natural vegetation to agriculture in recent decades.

Increasingly, these existing agricultural areas are now being converted to sugarcane for use in biofuel production. Brazil is now second only to the United States in ethanol production, much of which is used domestically.

What the effect on global climate would be if sugarcane farming were to expand significantly is not yet clear, said David Lobell, an assistant professor in environmental Earth system science at Stanford.

"The temperature changes are happening locally, where the land-use change is happening," Lobell said. "It does not seem to spill over into other countries, for example, at least as far as we can tell right now."

But Lobell said sugarcane growing in the Cerrado is definitely expanding and given that the region encompasses approximately 1.9 million square kilometers (733,000 square miles) – an area larger than Alaska – the potential exists for a globally significant effect.

Using maps and data from hundreds of satellite images, the researchers calculated the temperature, the amount of water given off and how much light was reflected rather than absorbed for each of the different types of vegetation. They found that compared to land cultivated with other annual crops, sugarcane reduced the local air temperature by an average of 0.93 degrees Celsius (1.67 F).

But compared to the natural vegetation of the Cerrado – mainly grass and shrubs – the sugarcane fields warmed the ambient air by 1.55 C (2.79 F).