Aerosols Play Large Role In Climate Cooling

Had airborne aerosols not spurred plant growth, atmospheric carbon dioxide could have risen as much as 50% more than it did in the past two centuries, according to a new study (Science, DOI: 10.1126/science.1207374).

Industrial processes and biomass burning emit aerosols into the atmosphere. The particles may also nucleate from gaseous chemicals released by a variety of industrial and natural sources. Regulators try to limit aerosol levels because the particles can irritate people’s lungs and cause other health problems. Aerosols also play a role in cooling climate by reflecting sunlight, seeding clouds, and carrying nutrients that, when deposited into ecosystems, enable CO₂-sequestering plants to grow.

By analyzing published data on nutrients deposited into different ecosystems and models of the role that aerosols play in their deposition, Natalie Mahowald, a climate science professor at Cornell University, estimated that aerosol-promoted plant growth cools the climate by about 0.5 watts per square meter. That’s equivalent to removing about 7 to 50 ppm of CO₂ from the atmosphere, based on climate models. Since the industrial revolution, CO₂ levels have risen by about 100 ppm.

Mahowald says the results suggest that reducing CO₂ is likely to become even more difficult and costly as policymakers seek to cut aerosols to improve air quality. “We have to clean up the aerosols because of public health concerns,” Mahowald says. “But that’s going to make things worse for the climate.”