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ArticlesOcean temperatures and sea level increases 50 percent higher than previously estimated
Ocean temperatures and sea level increases 50 percent higher than previously estimated
Atmosphere
LIVERMORE,
Calif. - New research suggests that ocean temperature and
associated sea level increases between 1961 and 2003 were
50 percent larger than estimated in the 2007 Intergovernmental
Panel on Climate Change report.
The
results are reported in the June 19 edition of the journal
Nature. An international team of researchers, including Lawrence
Livermore National Laboratory climate scientist Peter Gleckler,
compared climate models with improved observations that show
sea levels rose by 1.5 millimeters per year
in the period from 1961-2003. That equates to an approximately
2½-inch increase in ocean levels in a 42-year span.
The ocean
warming and thermal expansion rates are more than
50 percent larger than previous estimates for the upper 300
meters of oceans.
The
research corrected for small but systematic biases recently
discovered in the global ocean observing system,
and uses statistical techniques that “infill”
information in data-sparse regions. The results increase scientists’
confidence in ocean observations and further demonstrate that
climate models simulate ocean temperature
variability more realistically than previously thought.
a. The components are
thermal expansion in the upper 700 m (red), thermal expansion
in the deep ocean (orange), the ice sheets of Antarctica and
Greenland (cyan), glaciers and ice caps (dark blue) and terrestrial
storage (green). b. The estimated sea levels are indicated
by the black line (this study), the yellow dotted line and
the red dotted line (from satellite altimeter observations).
The sum of the contributions is shown by the blue line. Estimates
of one standard deviation error for the sea level are indicated
by the grey shading. For the sum of components, rigorous estimates
of one standard deviation error for upper-ocean thermal expansion
are included; these are shown by the thin blue lines. All
time series were smoothed with a three-year running average
and are relative to 1961.
“This
is important for the climate modeling community because it
demonstrates that the climate models used for assessing
sea-level rise and ocean warming
tie in closely with the observed results,” Gleckler
said.
Climate
model data were analyzed from 13 different modeling groups.
All model data were obtained from the WCRP CMIP3 multi-model
dataset archived at the LLNL’s Program for Climate
Model Diagnosis and Intercomparison (PCMDI).
Although
observations and models confirm that recent warming is greatest
in the upper ocean, there are widespread observations of warming
deeper than 700 meters.
Results
were compared with recent estimates of other contributions
to sea-level rise including glaciers, ice caps, Greenland
and Antarctic ice sheets, and thermal expansion changes in
the deep ocean. When these independent lines of evidence are
examined collectively, the story is more consistent than found
in earlier studies.
The
oceans store more than 90 percent of the heat in the Earth’s
climate system and act as a temporary buffer against the effects
of climate change. The ocean warming and
thermal expansion rates are 50 percent larger than previous
estimates for the upper 700 meters of oceans, and greater
than that for the upper 300 meters.
“This
is just the tip of the iceberg, so to speak,” Gleckler
said. “Our ability to quantify structural uncertainties
in observationally based estimates is critically important.
This study represents important progress.”
The
team involved researchers from the Centre for Australian Weather
and Climate Research (CSIRO), the Antarctic Climate and Ecosystems
Cooperative Research Centre and LLNL.
Founded
in 1952, Lawrence Livermore National Laboratory is a national
security laboratory, with a mission to ensure national security
and apply science and technology to the important issues of
our time. Lawrence Livermore National Laboratory is managed
by Lawrence Livermore National Security, LLC for the U.S.
Department of Energy's National Nuclear Security Administration.
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