Study finds large-scale ramp-up in biofuel crops could result in warming in some tropical regions, cooling in temperate and polar regions
Global land-use changes caused by a major ramp-up in biofuel crops—enough to meet about 10% of the world’s energy needs—could make some regions warmer, according to a new integrated modeling study by researchers from MIT and the Marine Biological Laboratory, Woods Hole.
Using an integrated assessment model that links an economic model with climate, terrestrial biogeochemistry, and biogeophysics models, the team examined the biogeochemical and biogeophysical effects of possible land use changes from an expanded global second-generation bioenergy program on surface temperatures over the first half of the 21st century.
The model shows that land clearing, especially forest clearing, has two concurrent effects: increased GHG emissions, resulting in surface air warming; and large changes in the land’s reflective and energy exchange characteristics, resulting in surface air warming in the tropics but cooling in temperate and polar regions.
While overall, these biogeochemical and biogeophysical effects will only have a small impact on global mean surface temperature, the model projects regional patterns of enhanced surface air warming of up to 1.5 °C in the Amazon Basin and the eastern part of the Congo Basin. Therefore, the researchers concluded, global land use strategies that protect tropical forests could significantly reduce air warming projected in these regions.
This tropical warming is made worse with more deforestation, which also causes a release of carbon dioxide, further contributing to the warming of the planet. Meanwhile, Arctic regions might generally experience cooling caused by an increase in reflectivity from deforestation.
Because all actions have consequences, it’s important to consider that even well-intentioned actions can have unintended negative consequences. It’s easy to look at a new, cleaner energy source, see how it will directly improve the climate, and stop there without ever considering all the ramifications. But when attempting to mitigate climate change, there’s more to consider than simply substituting out fossil fuels for a cleaner source of energy.—Willow Hallgren, lead author
Hallgren and her colleagues considered two scenarios: one where more forests are cleared to grow biofuel crops, and one where forests are maintained and cropland productivity is intensified through the use of fertilizers and irrigation.
In both cases, the researchers found that at a global scale, greenhouse-gas emissions increase—in the form of more carbon dioxide when CO2-absorbing forests are cut, and in the form of more nitrous oxide from fertilizers when land use is intensified. But this global warming is counterbalanced when the additional cropland reflects more sunlight, causing some cooling. Additionally, an increase in biofuels would replace some fossil fuel-based energy sources, further countering the warming.
Emphasizing changes not only globally, but also regionally, is vitally important when considering the impacts of future energy sources. We’ve found the greatest impacts occur at a regional level.—Willow Hallgren
Hallgren, W., C. A. Schlosser, E. Monier, D. Kicklighter, A. Sokolov, and J. Melillo (2013) Climate impacts of a large-scale biofuels expansion, Geophys. Res. Lett., 40, doi: 10.1002/grl.50352