April 17, 2011
Scientists with the Carnegie Institutions’s Department of Global Ecology at Stanford University and the University of Montana analyzed temperature, reflectivity, and evapotranspiration from satellite data across 733,000 square miles—an area larger than the state of Alaska. They found converting from natural cerrado grassland vegetation to crop/pasture on average triggered warming of 2.79 °F (1.55 °C), but that subsequent conversion to sugarcane, cooled the surrounding air by an average of 1.67 °F (0.93°C).
"We found that shifting from natural vegetation to crops or pasture results in local warming because the plants give off less beneficial water. But the bamboo-like sugarcane is more reflective and gives off more water—much like the natural vegetation," said Carnegie's Scott Loarie, lead author of the research. "It’s a potential win-win for the climate—using sugarcane to power vehicles reduces carbon emissions, while growing it lowers the local air temperature."
"The beneficial effects are contingent on the fact sugarcane is grown on areas previously occupied by crops or pastureland, and not in areas converted from natural vegetation," stated a press release from the Carnegie Institution. "It is also important that other crops and pastureland do not move to natural vegetation areas, which would contribute to deforestation."
The findings suggest that Brazil's sugar cane ethanol industry, which powers a quarter of the country's automobile fleet, has even more benefits than previously believed. Sugar cane ethanol has significantly lower carbon dioxide emissions than conventional gasoline.
The research also indicates the importance in accounting for non-fossil fuel-based climate impacts.
"It’s becoming increasingly clear that direct climate effects on local climate from land-use decisions constitute significant impacts that need to be considered core elements of human-caused climate change," said coauthor Greg Asner, also of the Carnegie Institution.
The cerrado is a woody savanna that covers 20 percent of Brazil. Conversion of cerrado for agriculture and cattle pasture has emerged as one of Brazil's biggest sources of greenhouse gas emissions in recent years. Cerrado loss has outpaced that of the Amazon rainforest.