An international team of 21 authors from 17 institutions in seven countries, including Western Washington University’s Andy Bunn, has just published a study in the journal “Nature Climate Change” showing that, as the cover of snow and ice in the northern latitudes has diminished in recent years, the temperature over the northern land mass has increased, causing a reduction in temperature and vegetation seasonality in this area.
In other words, the temperature and vegetation at northern latitudes are increasingly resembling those found several degrees of latitude farther south as recently as 30 years ago.
"Our work confirms a growing and solid body of evidence showing that warming in the Arctic is having sooner than expected – and stronger than expected – impacts. The changes in the north are shocking even for a science community used to studying a dynamic planet,” said Bunn.
The study was funded by NASA’s Earth Science Division and is based on newly improved ground and satellite data sets. It examines critically the relationship between changes in temperature and vegetation productivity in northern latitudes.
On the amplified greenhouse effect, Ranga Myneni of Department of Earth and Environment at Boston University and lead co-author, said, “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. 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.”
“The amplified warming in the circumpolar area roughly above the Canada-USA border is reducing temperature seasonality over time because the colder seasons are warming more rapidly than the summer,” said Liang Xu, a Boston University doctoral student and lead co-author of the study.
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 north—a reduction in vegetation seasonality of about seven degrees south in latitude,” said co-author Terry Chapin, professor emeritus at the 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 at the Royal Swedish Academy of Sciences and the University of Sheffield.
A key finding of this study is an accelerating greening rate in the Arctic and a decelerating rate in the boreal region, despite a nearly constant rate of temperature seasonality diminishment in these regions over the past 30 years. “This may portend a decoupling between growing season warmth and vegetation productivity in some parts of the North as the ramifications of amplified greenhouse effect — including permafrost thawing, frequent forest fires, outbreak of pest infestations, and summertime droughts — come in to play,” said co-author Hans Tømmervik, a senior researcher at the Norwegian Institute for Nature Research in Tromsø.
According to the authors, the future does indeed look troubling: Based on analysis of 17 state-of-the-art climate model simulations, diminishment of temperature seasonality in these regions could be more than 20 degrees in latitude by the end of this century relative to the 1951-1980 reference period. The projected temperature seasonality decline by these models for the 2001-2010 decade is actually less than the observed decline.
“These changes will affect local residents through changes in provisioning ecosystem services such as timber and traditional foods,” said Research Professor Bruce Forbes of the University of Lapland in Rovaniemi, Finland. They will also impact the global community through changes in regulatory ecosystem services relating to emissions of greenhouse gases.
“The way of life of many organisms on Earth is tightly linked to seasonal changes in temperature and availability of food, and all food on land comes first from plants,” said Scott Goetz, deputy director and senior scientist the Woods Hole Research Center in Falmouth, Mass. “Think of migration of birds to the Arctic in the summer and hibernation of bears in the winter: Any significant alterations to temperature and vegetation seasonality are likely to impact life not only in the north but elsewhere in ways that we do not yet know.”
The research paper can be viewed at http://cliveg.bu.edu/greeningearth/ssnltydim/ssnlty-dim.html or at the Nature website at http://www.nature.com/nclimate/index.html.
Bunn’s work on studying climate change in the north includes his work on multinational effort called The Polaris Project that takes researchers and undergraduates to Siberia each summer. For more information on the Polaris Project, go to http://www.thepolarisproject.org/.
For more information, contact Andy Bunn at firstname.lastname@example.org.