Well look at that. We’re getting to the point there isn’t much room left for CO2-forced warming at all after accounting for black soot, brown soot, land use change, urban heat islands, cloud cover changes and solar effects. Does carbon dioxide have any net effect? We’re still not sure.
Scientists have found that fossil fuel and biomass combustion, whether from forest fires or from wood-burning stoves, has a larger impact on the climate than previously considered.
Wildfires, such as the recent blazes in the western United States, along with millions of stoves across the developing world, dirty engines and aging generators, can kick up soot in vast quantities. These black carbon clouds rising from burning organic matter have long been understood to influence the climate by absorbing sunlight and heat. When suspended in the atmosphere, these particles also shield the ground from sunlight, preventing water from evaporating and stalling the hydrological cycle.
But dark smoke isn’t the only climate forcer from these sources, and researchers have found that other biomass emissions, particularly from “brown carbon,” have an overlooked impact on the warming planet, according to research published earlier this week in Proceedings of the National Academy of Sciences.
The study, led by Chul Chung, from the Gwangju Institute of Science and Technology in South Korea, looked at how warming results from carbon that isn’t completely charred to its elemental state. “Basically, when you have fires or smoke, first you see the smoke is black in color when it’s flaming,” explained Veerabhadran Ramanathan, a co-author of the study. “Then the smoke after that is whitish. The white stuff is what is called organic particles.”
Scientists previously treated these emissions solely as sunlight reflectors and presumed that these emissions had a cooling effect on the climate. But Ramanathan, a distinguished climate scientist at the Scripps Institution of Oceanography at the University of California, San Diego, said the white smoke isn’t as white as it seems and absorbs more energy than many researchers calculated, meaning it could affect how the planet warms.
“We were convinced [climate impacts were] there; the question was, how do you get a number on the global effect?” he said.
To find out, the researchers used satellite data along with ground-based aerosol sensors and aircraft measurements to determine how much heat brown carbon can soak up. The researchers found that organic matter emissions roughly break even with their light scattering offsetting their absorption so their net climate impact is close to zero. This means that climate forcing from black carbon is 85 percent higher than what the Intergovernmental Panel on Climate Change estimated.