An international team of authors from 17 institutions in seven countries, including the Woods Hole Research Center, published a study in the journal Nature Climate Change on the 10 March 2013 (10.1038/NCLIMATE1836: http://www.nature.com/nclimate). The study shows 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 at different rates during the four seasons, causing a reduction in temperature and vegetation seasonality in this area. The temperature and vegetation at northern latitudes increasingly resemble those found several degrees of latitude farther south as recently as 30 years ago.
The NASA-funded study, based on newly improved ground and satellite data sets, examines critically the relationship between changes in temperature and vegetation productivity in northern latitudes. "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," says Liang Xu, a Boston University doctoral student and lead co-author of the study. 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—creating large patches of vigorously productive vegetation totaling more than a third of the northern landscape—over 9 million km2, which is roughly about the area of the USA.
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. "Some areas of boreal forest will be negatively impacted by warming temperatures, from increased drought stress as well as insect and fire disturbance, but this work shows that in most high latitude regions we see increased productivity resulting from a reduced range of seasonal temperature variability," says co-author Scott Goetz, a senior scientist at the Woods Hole Research Center. Dr. Goetz's research focuses on ecosystem responses to environmental change, including monitoring and modeling the linkages and feedbacks between forests and climate, land use change and disturbance.
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," says co-author Prof. Terry Chapin, Professor Emeritus, University of Alaska, Fairbanks. The change equates to a distance of approximately 480 miles southward.
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. These changes will affect local residents as change occurs in ecosystem services, such as in timber and traditional food production, as a result of warming temperatures. They will also impact the global community through changes in regulatory ecosystem services relating to emissions of greenhouse gases.
About the Woods Hole Research Center—WHRC is a private, non-profit research organization focusing on environmental sciences. Our scientists combine analysis of satellite images of the Earth with field studies to measure, model, and map changes in the world's ecosystems, from the thawing permafrost in the Arctic to the expanding agriculture regions of the tropics. We work locally and regionally, with in-depth expertise and collaborations in North and South America and Africa; and we also work globally, focusing on how humans are changing global cycles of carbon, nitrogen, and water. We merge natural science with economics to discover sustainable paths for human prosperity and stewardship of the Earth's natural resources.
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