Human emissions of greenhouse gases are driving rapid warming all over the globe — particularly in the Arctic, where temperatures are rising at about twice the global rate. But there's another form of carbon in the atmosphere that may also be playing a role.

Black carbon particles, or soot, are collecting in the pristine Arctic, darkening the surface of the snow and ice and causing it to absorb more heat. Scientists believe that black carbon may be causing the region to warm and melt even faster than it otherwise would as the climate continues to change.

Researchers, aided by models of the atmosphere, have suggested that black carbon pollution may come from a variety of sources — some from industry-related fossil fuel burning, some from wood burning by humans and some from wildfires.

Pinpointing the exact sources of the pollution is important for policymakers working on addressing the problem. Members of the Arctic Council — made up of eight nations with geographic ties to the region, including the United States — signed a declaration in 2017 calling for reductions in black carbon emissions. It was an attempt to help slow Arctic warming.

Now, new research is helping to narrow it down. A study published this week in Science Advances finds clear seasonal differences in the sources of black carbon pollution in the Arctic. In the summer, biomass burning — including wildfires, which some scientists warn may become more common in the Arctic as temperatures rise — seems to be the dominant contributor.

In the winter, pollution levels rise substantially, and fossil fuels become the biggest source.

Overall, averaged across the year, fossil fuel burning — likely from nations throughout the Northern Hemisphere, including Russia, China, Europe and the United States — remains the biggest source. It likely accounts for about 70 percent of year-round black carbon pollution in the Arctic, the research suggests.

The new study drew from on-site measurements of black carbon pollution, collected at a handful of sites in Alaska, Canada, Sweden and Siberia. The researchers collected data on black carbon concentrations in the atmosphere, and they conducted chemical analyses of soot samples to determine what process produced them.

The researchers compared their findings to model simulations of black carbon in the Arctic — the simulations generally rely on reports, or inventories, of black carbon emissions from both human activities and wildfires in the Northern Hemisphere. They found that the observations and the models agree well with one another when it comes to the amount of black carbon that's actually ending up in the Arctic.

On the other hand, they found that the models may not be doing as good a job of determining where the carbon is coming from. As a result, the researchers note that relying on the models alone could lead scientists and policymakers to overestimate the amount of soot that's contributed by biomass burning and wildfires, as opposed to fossil fuels.

That's not to say both aren't important — biomass burning still has a significant effect, particularly in the summertime when total pollution levels tend to be lower — but fossil fuels remain largely the dominant contributor.

Another climate feedback

Research has found that black carbon emissions may be responsible for as much as half a degree Celsius of Arctic warming — that's about a quarter of the warming the Arctic has experienced over the last hundred years. The same study found that targeted efforts to reduce black carbon and other pollutants could prevent about 0.2 C of Arctic warming by 2050.

Black carbon particles are known to influence local warming in two main ways. While they only last a short time in the atmosphere, they can trap heat while they're floating around in the air — its temporary influence has been found to be far more powerful than carbon dioxide. And when they fall to Earth, they can darken the surfaces where they land and cause them to absorb more heat.

Studies have found that the latter process is the biggest problem in the Arctic. Because the region contains so much snow and ice, it tends to reflect a lot of sunlight. When soot darkens these reflective surfaces, it causes them to warm up and melt at faster rates.

As snow and ice melts, the Arctic's reflective surfaces shrink even further, and the landscape absorbs even more heat. In this way, enhanced melting can turn into a kind of feedback loop that begets more and more melting over time.

Targeted efforts to reduce black carbon emissions, especially in the far North, may help to slow this process. That said, the melting would still be happening without it as long as global temperatures continue to rise.

Recent research has warned that unless global greenhouse gas emissions begin falling substantially within the next decade or two, winter temperatures in the Arctic could skyrocket by more than 10 C. Continued emissions of greenhouse gases remain the greatest threat to the rapidly warming Arctic.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.