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September 3, 2003
Ocean May Sponge Up Some Warmth Over Next 50 Years
NASA's improved global climate computer model, which simulates and projects
how the Earth's climate may change, indicates that the oceans have been
absorbing heat since 1951 and will continue to absorb more heat from
the atmosphere over the next 50 years. This increasing ocean heat storage
suggests that global surface temperatures may warm less than previous
studies projected, while the ocean acts as a bigger heat sponge. Further,
such additional ocean heating would likely change regional climate patterns.
Shan Sun and James Hansen, both of NASA's Goddard Institute for Space
Studies, New York, NY, used NASA's Global Climate Model (GCM), one of
the world's leading computer climate models that simulate past and potential
future climate changes. The GCM has been enhanced with new "ocean models" that
better simulate how oceans currently absorb heat and will respond to
a warming global climate. The study appears in the latest issue of the
American Meteorological Society's Journal of Climate.
One of the leading reports on climate change, the Intergovernmental
Panel on Climate Change (IPCC) report of 2001, suggests that between
the years 1990 and 2100 the world's average temperature will rise between
0.6 and 2.5 degrees Celsius (C) or 1.1 and 4.5 Fahrenheit (F). "The enhanced
GCM shows that the average global temperature would rise between 0.4
and 1.2 C (between 0.7 and 2.2 F) through the year 2050, for plausible
increases of greenhouse gases," Sun said.
Scientists measure ocean heat storage in Watts per meter squared, the
rate of heating a square meter area. For example, a miniature Christmas
tree bulb dissipates about 1 Watt of energy, so one bulb over every square
meter would heat at a rate of 1 Watt per meter squared.
The enhanced GCM showed the world's oceans were storing heat at a rate
of about 0.2 Watts per square meter in 1951, and in the past 50 years,
as atmospheric temperatures warmed, the rate of heat storage increased
to about .75 Watts per square meter, capturing more heat from the atmosphere. "This
increase in ocean heat storage shows that the planet is out of energy
balance," Hansen said. "This energy imbalance implies that the atmosphere
and ocean will continue to warm over time, so we will see continuing
climate change."
It is important to know accurately how much heat oceans are storing,
because the amount of heat stored provides a measurement of the Earth's
energy imbalance and indicates how much global temperature may increase
in the future. It's also important to see where heat is increasing in
the world's oceans, in order to predict climate changes in various geographical
regions.
Sun and Hansen also looked at changes of precipitation and ocean currents,
other factors that warmer world-wide waters may impact. If greenhouse
gases continue to increase rapidly, the model projects significant ocean
warming during the next 50 years in the Eastern Pacific Ocean, off the
U.S. west coast, which could have biological consequences for ocean life.
The results also project increased precipitation and evaporation over
the North Atlantic Ocean, increasing the fresh water in the region. An
increase in freshwater has long been suspected as something that could
weaken the northward transport of heat by the Atlantic Ocean, thus causing
Europe to become cooler, even while the world becomes warmer. Sun and
Hansen find, however, that the ocean circulation does not weaken significantly
according to their model, so they expect no cooling effect on Europe.
More monitoring of ocean temperatures is needed to further the studies
of ocean behavior. Ocean temperature readings currently do not reach
full ocean depths, as is needed to increase the accuracy of future predictions.
With the new Ocean Models included in the GCM, if measurements of the
amount of heat held by oceans are improved, it may be possible to begin
to better quantify the Earth's changing radiation imbalance and its causes
with an accuracy of about one decade.
This study was funded through NASA's Earth Science Enterprise under
NASA's Climate and Oceanography Programs. The mission of NASA's Earth
Science Enterprise) is to develop a scientific understanding of the Earth
system and its response to natural or human-induced changes to enable
improved prediction capability for climate, weather, and natural hazards.
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Contacts:
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-4044) |
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Global Sea Surface Temperatures
This is an image of global sea surface temperatures taken from Japan
National Space Development Agency's (NASDA) AMSR-E instrument aboard
NASA's Aqua spacecraft on August 27, 2003. The colors in this false-color
map represent temperatures of the ocean's surface waters, ranging from
a low of -2°C (28°F) in the darkest green areas to a high of
35°C (95°F) in the brightest yellow-white regions. Sea ice is
shown as white and land is dark gray. CREDIT: NASDA/NASA
An Ocean of Change
An enhanced "ocean climate model" showing how the ocean behaves to changes
in atmospheric temperature indicates that the ocean may absorb more heat
as the climate warms. This National Weather Service photo depicts a turbulent
sea surface in the North Pacific during a storm. CREDIT: NOAA/Historic
NWS Collection
Surface Air Temperature Changes
This graph shows how greenhouse gases (GHGs) increased global surface
temperature from 1950-2000 and are projected to increase temperature
through 2050. The simulated warming of the past 50 years depends on whether
5 or 6 "forcings" (GHGs, volcanoes, solar changes) are used, the 6th
being tropospheric aerosols. The future warming may be between 0.4 and
1.2C (0.7 and 2.2 F), depending mainly on whether GHGs increase rapidly
(BAU scenario) or at a constant rate (ALT scenario). CREDIT: NASA/GISS
Global Sea Surface Temperature
The moderate-resolution Imaging Spectroradiometer (MODIS) instrument
onboard NASA's Terra and Aqua satellites provides the most detailed measurements
ever made of sea surface temperature. In this image, cold waters are
black and dark green. Blue, purple, red, yellow, and white represent
progressively warmer water. CREDIT: NASA
High-Resolution Image(16 MB TIFF)
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