"As a result of the enhanced warming over a longer ground-thaw season, the total amount of heat available for plant growth in these northern latitudes is increasing. This created during the past 30 years large patches of vigorously productive vegetation, totaling more than a third of the northern landscapeover 9 million km2, which is roughly about the area of the USA resembling the vegetation that occurs further to the south," says Dr. Compton Tucker, Senior Scientist, NASA's Goddard Space Flight Center, Greenbelt, Maryland.
The authors measured seasonality changes using latitude as a yardstick. They first defined reference latitudinal profiles for the quantities being observed and then quantified changes in them over time as shifts along these profiles.
"Arctic plant growth during the early-1980s reference period equaled that of lands north of 64 degrees north. Today, just 30 years later, it equals that of lands above 57 degrees northa reduction in vegetation seasonality of about seven degrees south in latitude," says co-author Prof. Terry Chapin, Professor Emeritus, University of Alaska, Fairbanks. "This manner of analyses suggested a decline in temperature and vegetation seasonality of about four to seven degrees of latitude during the past 30 years," says co-author Eugenie Euskirchen, Research Professor, University of Alaska, Fairbanks.
"The reduction of vegetation seasonality, resulting in increased greenness in the Arctic, is visible on the ground as an increasing abundance of tall shrubs and tree incursions in several locations all over the circumpolar Arctic," says co-author Terry Callaghan, Professor, Royal Swedish Academy of Sciences and the University of Sheffield, UK. He notes that the greening in the adjacent Boreal areas is much less conspicuous in North America than in Eurasia.
A key finding of this study is an accelerating greening rate in the Arctic and a decelerating rat
|Contact: Ranga Myneni|