Brown carbon aerosols dominate particulate emissions from the burning of Alaskan and Siberian peatlands. They physically occur as amorphous "tar balls" with negligible black carbon mixing. They absorb very strongly in the shorter visible wavelengths, characterized by a mean Ångström coefficient of ≈ 9. These aerosols could result in a net warming of the atmosphere, provided the albedo of the underlying surface is greater than 0.6.