Dr. James Hansen has never been shy about standing up for his scientific principles. In 1988, speaking before Congress, Dr. Hansen laid out a blunt truth, “It is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here.” The statement caused an eruption of controversy, but time has borne out the sad truth of these words.

As the environmental ministers of the Arctic nations, including the United States, meet in Sweden next week, they have an opportunity to show leadership on an important though less well-known climate pollutant, black carbon (soot).

While carbon dioxide remains the most important, long-lasting pollutant forcing climate change, recent studies have revealed that short-lived climate forcers like black carbon are equally damaging, especially in the Arctic.

The mention of soot conjures images of black clouds pouring out of unfiltered cars, or of cities lost in dark fog. At times in our history, soot pollution has helped stain entire ecosystems black, famously causing moths in Britain to change color from white to black to better hide in their environment. These images are well-deserved: soot is dangerous to both humans and the environment.