| October 23, 2003
Recent Warming of Arctic May Affect Worldwide Climate
Recently observed change in Arctic temperatures and sea ice cover may
be a harbinger of global climate changes to come, according to a recent
NASA study. Satellite data — the unique view from space — are
allowing researchers to more clearly see Arctic changes and develop an
improved understanding of the possible effect on climate worldwide.
The Arctic warming study, appearing in the November 1 issue of the American
Meteorological Society’s Journal of Climate, shows that compared to the
1980s, most of the Arctic warmed significantly over the last decade,
with the biggest temperature increases occurring over North America.
“The new study is unique in that, previously, similar studies made use
of data from very few points scattered in various parts of the Arctic
region,” said the study’s author, Dr. Josefino C. Comiso, senior research
scientist at NASA’s Goddard Space Flight Center, Greenbelt, Md. “These
results show the large spatial variability in the trends that only satellite
data can provide.” Comiso used surface temperatures taken from satellites
between 1981 and 2001 in his study.
The result has direct connections to NASA-funded studies conducted last
year that found perennial, or year-round, sea ice in the Arctic is declining
at a rate of nine percent per decade and that in 2002 summer sea ice
was at record low levels. Early results indicate this persisted in 2003.
Researchers have suspected loss of Arctic sea ice may be caused by changing
atmospheric pressure patterns over the Arctic that move sea ice around,
and by warming Arctic temperatures that result from greenhouse gas buildup
in the atmosphere.
Warming trends like those found in these studies could greatly affect
ocean processes, which, in turn, impact Arctic and global climate, said
Michael Steele, senior oceanographer at the University of Washington,
Seattle. Liquid water absorbs the Sun’s energy rather than reflecting
it into the atmosphere the way ice does. As the oceans warm and ice thins,
more solar energy is absorbed by the water, creating positive feedbacks
that lead to further melting. Such dynamics can change the temperature
of ocean layers, impact ocean circulation and salinity, change marine
habitats, and widen shipping lanes, Steele said.
In related NASA-funded research that observes perennial sea-ice trends,
Mark C. Serreze, a scientist at the University of Colorado, Boulder,
found that in 2002 the extent of Arctic summer sea ice reached the lowest
level in the satellite record, suggesting this is part of a trend. “It
appears that the summer 2003 -- if it does not set a new record -- will
be very close to the levels of last year,” Serreze said. “In other words,
we have not seen a recovery; we really see we are reinforcing that general
downward trend.” A paper on this topic is forthcoming.
According to Comiso’s study, when compared to longer term ground-based
surface temperature data, the rate of warming in the Arctic over the
last 20 years is eight times the rate of warming over the last 100 years.
Comiso’s study also finds temperature trends vary by region and season.
While warming is prevalent over most of the Arctic, some areas, such
as Greenland, appear to be cooling. Springtimes arrived earlier and were
warmer, and warmer autumns lasted longer, the study found. Most importantly,
temperatures increased on average by 1.22 degrees Celsius per decade
over sea ice during Arctic summer. The summer warming and lengthened
melt season appears to be affecting the volume and extent of permanent
sea ice. Annual trends, which were not quite as strong, ranged from a
warming of 1.06 degrees Celsius over North America to a cooling of .09
degrees Celsius in Greenland.
If the high latitudes warm, and sea ice extent declines, thawing Arctic
soils may release significant amounts of carbon dioxide and methane now
trapped in permafrost, and slightly warmer ocean water could release
frozen natural gases in the sea floor, all of which act as greenhouse
gases in the atmosphere, said David Rind, a senior researcher at NASA’s
Goddard Institute of Space Studies, New York. “These feedbacks are complex
and we are working to understand them,” he added.
The surface temperature records covering from 1981 to 2001 were obtained
through thermal infrared data from National Oceanic and Atmospheric Administration
satellites. The studies were funded by NASA’s Earth Science Enterprise,
which is dedicated to understanding the Earth as an integrated system
and applying Earth System Science to improve prediction of climate, weather
and natural hazards using the unique vantage point of space.
For more information and images on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2003/1023esuice.html
and
http://www.earth.nasa.gov
###
Contacts:
Elvia H. Thompson
Headquarters, Washington
(Phone: 202/358-1696)
Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 607/273-2561) |
|
Changing Seasons, Changing Ice
Arctic perennial sea ice has been decreasing at a rate of 9% per decade.
The first image shows the minimum sea ice concentration for the year
1979, and the second image shows the minimum sea ice concentration in
2003. The data used to create these images and the following animation
were collected by the Defense Meteorological Satellite Program (DMSP)
Special Sensor Microwave Imager (SSMI). Credit: NASA
1979
High-Resolution Image
2003
High-Resolution Image
1979 to 2003 Sea Ice Comparison
This animation shows the annual minimum sea ice extent and concentration
for 24 years, from 1979 to 2003. The year 2002 showed lowest level of
sea ice on record. Credit: NASA
High-Resolution
Still Image
Warmer and Cooler
This animation shows surface temperature anomalies in the Arctic for
each year from 1981 through 2002. The orange and red colors represent
an increase of 0 to 7 degrees C, while the blue colors represent a decrease
of 0 to 7 degrees. Each color step indicates a change of 0.25 degrees
Celsius. The data used to create images 5, 6, and 7 were collected by
the AVHRR instruments onboard the NOAA POES satellites. Credit: NASA
Sea Ice Concentration
Sea ice extent reached a record minimum in September, 2002, and retreated
to almost the same position in September, 2003, as observed using satellite
passive microwave data. The absence of ice off Greenland is particularly
unusual. Sea ice concentration in the western sector of the Arctic Ocean
was anomalously low as well. Credit: NSIDC
High-Resolution
Image
Pressure to Change
This animation shows overall warming and cooling trends in the Arctic
over a 22-year period from August 1981 to July 2002. The orange and red
colors represent an increase of 0 to 0.4 degrees C, while the blue colors
represent a decrease of 0 to 0.4 degrees. Each color step indicates a
change of 0.02 degrees Celsius. Note that while much of the Arctic has
experienced warming, some regions exhibit an overall cooling pattern.
Credit: NASA
Low-Resolution
Still Image
High-Resolution
Still Image
Sea Ice Trends
Color-coded trends in the sea ice cover are shown for autumn, winter,
spring and summer using AVHRR surface temperature data from 1981 to 2001.
The trends are very positive in summer and mainly positive in autumn
and spring suggesting a change towards longer melt periods. In winter,
large areas are shown to have negative trends but these areas are also
where the sea ice cover has been increasing in winter during the same
period. Credit: NASA
Longer Melt Seasons
The length of the melt season inferred from surface temperature weekly
data has been increasing by 9, 12, 12, and 17 days per decade in sea
ice covered areas, Greenland, Eurasia (>60° lat), and North America
(>60° lat), respectively. Longer melt periods would mean reduced
growth season, thinner sea ice and less extensive sea ice cover in the
summer. Credit: NASA
The Global Role of the Polar Caps
This is a conceptual animation showing how polar ice reflects light from
the sun. As this ice begins to melt, less sunlight gets reflected into
space. It is instead absorbed into the oceans and land, raising the overall
temperature, and fueling further melting. Credit: NASA
Is the Ocean Rising?
This is a conceptual animation showing how melting ice on land and at
sea, can affect the surrounding ocean water, changing both the chemistry
and relative sea level. Credit: NASA |
