Industrial soot warmed the Arctic
Soot from coal burning in North America may have caused much of the warming in Greenland in the early 20th century, researchers reported online in Science Express on August 9.
The Arctic, including Greenland, warmed twice during the 20th century. A warm phase in recent decades parallels increases in greenhouse gas levels, but whether a similarly strong temperature rise early in the century was caused by natural cycles or by human activity has been unclear, notes climate scientist Richard Alley of Pennsylvania State University in a commentary published in the same issue.
The new study reveals that at its peak around 1910, soot created a warming effect throughout the Arctic that was about double the warming caused by current CO2 concentrations globally—3.2 watts per square meter (W/m2) compared with 1.6 W/m2.
A team led by Joseph McConnell of the Desert Research Institute collected ice cores from a region in Greenland with very high amounts of snowfall. The samples provided a detailed record of the annual deposition of black carbon going back to 1788.
Emissions of soot, also known as black carbon, ramped up after 1850 because of industrial expansion and remained high until 1950. Layers of black carbon on snow and ice absorb sunlight, causing a warming effect.
McConnell and colleagues melted sections of ice cores and analyzed the melt water for black carbon, vanillic acid (produced by forest fires), and forms of sulfur associated with fossil fuel burning. Before 1850, forest fires contributed most of the black carbon. After that, industrial emissions rose and peaked in 1906–1910, when industrial soot's warming effect was eight times that of forest fires. The soot's source was traced back to the eastern U.S. and Canada using weather records and models.
The amount of black carbon in the Arctic has declined since 1952, possibly because of cleaner combustion. Sulfur has also decreased since passage of the Clean Air Act in the U.S. in the early 1970s, the researchers noted. "The rise and fall of soot in Greenland illustrate the human ability both to alter our environment and to limit those alterations," Alley added.
