The upper layer of
the world’s ocean has warmed steadily since 1993, indicating a
strong climate change signal, according to a new study. The energy
stored is enough to power nearly 500 100-watt light bulbs per each
of the roughly 6.7 billion people on the planet.
“We are seeing the global ocean store more heat than it gives
off,” said John Lyman, an oceanographer at NOAA’s Joint Institute
for Marine and Atmospheric Research, who led an international team
of scientists that analyzed nine different estimates of heat
content in the upper ocean from 1993 to 2008.
The team combined the estimates to assess the size and certainty
of growing heat storage in the ocean. Their findings will be
published in the May 20 edition of the journal Nature.
The scientists are from NOAA, NASA, the Met Office Hadley Centre,
the University of Hamburg and the Meteorological Research
Institute in Japan.
Josh Willis, an oceanographer at the NASA Jet Propulsion
Laboratory and one of the scientists who contributed to the study
said: “The ocean is the biggest reservoir for heat in the climate
system, so as the planet warms, we’re finding that 80 to 90
percent of the increased heat ends up in the ocean.”
A warming ocean is a direct cause of global sea level rise, since
seawater
expands and takes up more space as it heats up,
accounting for about one-third to one-half of global sea level rise.
Combining multiple estimates of heat in the upper ocean – from
the surface to about 2,000 feet down – the team found a strong
multi-year warming trend throughout the world’s ocean. According
to measurements by an array of autonomous free-floating ocean
floats called Argo as well as by earlier devices called expendable
bathythermographs or XBTs that were dropped from ships to obtain
temperature data, ocean heat content has increased over the last
16 years. The team notes that there are still some uncertainties
and some biases.
Gregory Johnson, an oceanographer with NOAA’s Pacific Marine
Environmental Laboratory said: “The XBT data give us vital
information about past changes in the ocean, but they are not as
accurate as the more recent Argo data. However, our analysis of
the data gives us confidence that on average, the ocean has warmed
over the past decade and a half, signaling a climate imbalance.”
Data from the array of Argo floats – deployed by NOAA and other
U.S. and international partners – greatly reduce the
uncertainties in estimates of ocean heat content over the past
several years, the team said. There are now more than 3,200 Argo
floats distributed throughout the world’s ocean sending back
information via satellite on temperature, salinity, currents and
other ocean properties.
Notes to Editors
Robust Warming of the
Global
Upper
Ocean by John M. Lyman, Simon A. Good, Viktor V. Gouretski,
Masayoshi Ishii, Gregory C. Johnson, Matthew D. Palmer, Doug M.
Smith, and Josh K. Willis is published in Nature on 20th May 2010.
The Met Office Hadley Centre worked with the Joint Institute for
Marine and Atmospheric Research at the University of
Hawaii, NOAA/Pacific Marine Environmental Laboratory, the
University of
Hamburg, Climate Mteorological Research Institute,
Japan and NASA Jet Propulsion Laboratory.
The Met Office Hadley Centre advises the UK government on climate
change research. Its work is, in part, jointly funded by Defra
(Department for Environment, Food and Rural Affairs) and DECC
(Department for Energy and Climate Change).
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