A new study led by Carnegie Institution’s Department of Global Ecology has found that the expansion of sugarcane crop in Brazil in areas previously occupied by other Brazilian crops cools the local climate. It does so by reflecting sunlight back into space and by lowering the temperature of the surrounding air as the plants “exhale” cooler water. The study is published in the second issue of Nature Climate Change.
The research team, led by Carnegie’s Scott Loarie, is the first to quantify the direct effects on the climate from sugarcane expansion in areas of existing crop and pastureland of the cerrado, in central Brazil. Co-authors on the study are David Lobell of the Program for Food Security and the Environment at Stanford University; Gregory Asner and Christopher Field of Carnegie’s Department of Global Ecology; and Qiaozhen Mu of the University of Montana.
The researchers used data from hundreds of satellite images over 733,000 square miles—an area larger than the state of Alaska. They measured temperature, reflectivity (albedo), and evapotranspiration—the water loss from the soil and from plants as they exhale water vapor.
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. 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.
—Scott Loarie
The scientists found that converting from natural vegetation to crop/pasture on average warmed the cerrado by 2.79 °F (1.55 °C), but that subsequent conversion to sugarcane, on average, cooled the surrounding air by 1.67 °F (0.93°C).
The researchers emphasize that 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. It is also important that other crops and pastureland do not move to natural vegetation areas, which would contribute to deforestation.
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.
—Greg Asner
The work was made possible through the support of the Stanford University Global Climate and Energy Project.
Resources
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Scott R. Loarie, David B. Lobell, Gregory P. Asner, Qiaozhen Mu& Christopher B. Field (2011) Direct impacts on local climate of sugar-cane expansion in Brazil. Nature Climate Change doi: 10.1038/nclimate1067