A new study shows that intensive greenhouse effect has diminished the amount of ice in the North and raised temperatures to almost what the South experiences.
An international team of 21 authors from 17 institutions in seven countries has just published a study in the journal Natural Climate Change stating that due to intensive greenhouse effect, the temperature and vegetation at northern latitudes are becoming similar to those at southern latitudes.
"A greenhouse effect initiated by increased atmospheric concentration of heat-trapping gasses -- such as water vapor, carbon dioxide and methane -- causes the Earth's surface and nearby air to warm," Professor Ranga Myneni, Department of Earth and Environment, Boston University and lead co-author said. "The warming reduces the extent of polar sea ice and snow cover on the large land mass that surrounds the Arctic ocean, thereby increasing the amount of solar energy absorbed by the no longer energy-reflecting surface. This sets in motion a cycle of positive reinforcement between warming and loss of sea ice and snow cover, thus amplifying the base greenhouse effect"
During the study, seasonality changes were measured using latitude as a yardstick. The authors 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 north -- a reduction in vegetation seasonality of about seven degrees south in latitude," said co-author professor 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," said 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," said 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.
