In the Amazon Basin, at the beginning of each dry season in May, farmers start felling trees and clearing undergrowth. The damp vegetation dries out on the ground for a few months. Then, before the rains resume, the farmers set the vegetation on fire. Most of the burning occurs on vast estates. Areas kilometers across are cleared to make way for agriculture. Figure 1 shows one example from the state of Rondonia in western Brazil.
The clearances change more than what grows on the ground. Like other aerosols, smoke particles intercept solar radiation and increase the reflectivity of clouds. Both effects tend to cool Earth’s surface. However, like much in climate science, the overall impact of aerosols is complicated by feedbacks. For example, by cooling the surface, aerosols slow surface winds, thereby reducing the uptake of aerosols such as dust, sea spray, and pollen. Ignorance of aerosol effects is among...
