Amplified Greenhouse Effect Shifts North's Growing Seasons

March 10, 2013

Steve Cole
Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov

Kathryn Hansen
Goddard Space Flight Center, Greenbelt, Md.
301-286-1046
kathryn.h.hansen@nasa.gov

Ruth Marlaire
Ames Research Center, Moffett Field, Calif.
650-604-4709
ruth.marlaire@nasa.gov

RELEASE: 13-069

AMPLIFIED GREENHOUSE EFFECT SHIFTS NORTH'S GROWING SEASONS

WASHINGTON -- Vegetation growth at Earth's northern latitudes
increasingly resembles lusher latitudes to the south, according to a
NASA-funded study based on a 30-year record of land surface and newly
improved satellite data sets.

An international team of university and NASA scientists examined the
relationship between changes in surface temperature and vegetation
growth from 45 degrees north latitude to the Arctic Ocean. Results
show temperature and vegetation growth at northern latitudes now
resemble those found 4 degrees to 6 degrees of latitude farther south
as recently as 1982.

"Higher northern latitudes are getting warmer, Arctic sea ice and the
duration of snow cover are diminishing, the growing season is getting
longer and plants are growing more," said Ranga Myneni of Boston
University's Department of Earth and Environment. "In the north's
Arctic and boreal areas, the characteristics of the seasons are
changing, leading to great disruptions for plants and related
ecosystems."

The study was published Sunday in the journal Nature Climate Change.

Myneni and colleagues used satellite data to quantify vegetation
changes at different latitudes from 1982 to 2011. Data used in this
study came from NOAA's Advanced Very High Resolution Radiometers
(AVHRR) onboard a series of polar-orbiting satellites and NASA's
Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on
the Terra and Aqua satellites.

As a result of enhanced warming and a longer growing season, large
patches of vigorously productive vegetation now span a third of the
northern landscape, or more than 3.5 million square miles (9 million
square kilometers). That is an area about equal to the contiguous
United States. This landscape resembles what was found 250 to 430
miles (400 to 700 kilometers) to the south in 1982.

"It's like Winnipeg, Manitoba, moving to Minneapolis-Saint Paul in
only 30 years," said co-author Compton Tucker of NASA's Goddard Space
Flight Center in Greenbelt, Md.

The Arctic's greenness is visible on the ground as an increasing
abundance of tall shrubs and trees in locations all over the
circumpolar Arctic. Greening in the adjacent boreal areas is more
pronounced in Eurasia than in North America.

An amplified greenhouse effect is driving the changes, according to
Myneni. Increased concentrations of heat-trapping gasses, such as
water vapor, carbon dioxide and methane, cause Earth's surface, ocean
and lower atmosphere to warm. Warming reduces the extent of polar sea
ice and snow cover, and, in turn, the darker ocean and land surfaces
absorb more solar energy, thus further heating the air above them.

"This sets in motion a cycle of positive reinforcement between warming
and loss of sea ice and snow cover, which we call the amplified
greenhouse effect," Myneni said. "The greenhouse effect could be
further amplified in the future as soils in the north thaw, releasing
potentially significant amounts of carbon dioxide and methane."

To find out what is in store for future decades, the team analyzed 17
climate models. These models show that increased temperatures in
Arctic and boreal regions would be the equivalent of a 20-degree
latitude shift by the end of this century relative to a period of
comparison from 1951-1980.

However, researchers say plant growth in the north may not continue on
its current trajectory. The ramifications of an amplified greenhouse
effect, such as frequent forest fires, outbreak of pest infestations
and summertime droughts, may slow plant growth.

Also, warmer temperatures alone in the boreal zone do not guarantee
more plant growth, which also depends on the availability of water
and sunlight.

"Satellite data identify areas in the boreal zone that are warmer and
dryer and ����other areas that are warmer and wetter," said co-author
Ramakrishna Nemani of NASA's Ames Research Center in Moffett Field,
Calif. "Only the warmer and wetter areas support more growth."
Researchers did find found more plant growth in the boreal zone from
1982 to 1992 than from 1992 to 2011, because water limitations were
encountered in the latter two decades.

Data, results and computer codes from this study will be made
available on NASA Earth Exchange (NEX), a collaborative
supercomputing facility at Ames. NEX is designed to bring scientists
together with data, models and computing resources to accelerate
research and innovation and provide transparency.

For more information and images associated with this release, visit:

http://go.nasa.gov/12Amv2s


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