Ocean warming on the rise
Embargo 3am, press conference 10.00 am, Thursday 19 June
2008, Melbourne Museum
To read the background to this report,
view here.
For images,
view here.
During the past four decades, the oceans have been soaking up
heat,
expanding and rising at a rate about 50 per cent faster than previously
estimated by the IPCC, a team of Australian and US oceanographers has found.
The team’s research published in Nature today,
corrects errors in ocean temperature data that had led to conflict between
observed and simulated changes. The effect of major volcanic eruptions on ocean
temperature can even be clearly seen in the data.
The results will give policy makers more confidence in the
models and in
predictions of future sea level rise due to ocean warming.
The Nature report contributes to a body of work supporting
the climate
models used for the IPCC
projections. The Nature report and a suite of international observations
indicated that the rate of sea level rise is tracking near the upper limit of
IPCC projections. If that
continued global mean sea level would
rise by about 800 mm by 2100.
“The modellers and the observers had been debating for years.
Modellers felt that the trouble was in the observations; and observers thought
the models were wrong,” says Catia Domingues, from the CSIRO Wealth from Oceans
Flagship, the lead author on the paper and a CSIRO post-doctoral Fellow with the
Centre for Australian Weather and Climate Research.
“We have been able to account for biases in about 70% of the
ocean temperature data and that, combined with more sophisticated analysis
techniques, gives us far more reliable and accurate rates of ocean warming,”
says Catia.
“Our findings reveal that a reported significant 15-year
change in global ocean temperature between 1970 and 1985, which climate models
could not simulate, was not natural, but rather due to errors in the
observations”.
The errors in the ocean temperature data also concealed how
fast sea level has been rising due to ocean warming and subsequent thermal
expansion (think of the ocean as like the mercury in a thermometer).
“Uncovering a significantly larger thermal expansion
contribution for the top 700 m of the oceans helps to explain, for the first
time, the rate at which global sea level has risen from 1961 to 2003. “And this
outcome sheds light on one of the key uncertainties of
the 2007 IPCC AR4 report”.
The detective work of CSIRO's Dr Susan Wijffels and NASA's Dr
Josh Willis and others was also critical to arriving
at the more accurate estimates of ocean warming
described in Nature.
“Their team scrutinized millions of ocean observations,
tracked down small but systematic errors, and provided us with corrections,”
says Catia.
“More accurate ocean observations and increased confidence in
the models they underpin will help us to be better prepared for changes in our
living conditions, no matter where we reside, near or far from the oceans.”
Catia Domingues is one of 16 early-career scientists chosen
for Fresh Science, a national program sponsored by the Federal and Victorian
governments. She is presenting her research to the public for the first time at
the Melbourne Museum.
Media contacts: Catia Domingues on 0411 565 163,
catia.domingues@csiro.au;
Sarah Brooker on 0413 332 489; and Niall Byrne on 0417 131 977 or
niall@freshscience.org
Background information
Catia Domingues is the lead author of the paper. She is from
the CSIRO Wealth from Oceans Flagship, and an Office of the Chief Executive
CSIRO post-doctoral Fellow with the Centre for Australian Weather and Climate
Research
The science team included researchers from the Centre for
Australian Weather and Climate Research, the Antarctic Climate and Ecosystem
Cooperative Research Centre and the Lawrence Livermore National Laboratory,
California. Co-authors were John Church, Neil White, Peter Gleckler; Susan
Wijffels, Paul Barker and Jeff Dunn.
Abstract
Changes in
the climate system's energy budget are predominantly revealed in ocean
temperatures and the associated thermal expansion contribution to
sea-level rise. Climate models, however, do not reproduce the large
decadal variability in globally averaged ocean heat content inferred
from the sparse observational database, even when volcanic and other
variable climate forcings are included. The sum of the observed
contributions has also not adequately explained the overall
multi-decadal rise2. Here we report improved estimates of
near-global ocean heat content and thermal expansion for the upper 300 m
and 700 m of the ocean for 1950–2003, using statistical techniques that
allow for sparse data coverage and applying recent corrections
to reduce systematic biases in the most common ocean temperature
observations. Our ocean warming and thermal expansion trends for
1961–2003 are about 50 per cent larger than earlier estimates but about
40 per cent smaller for 1993–2003, which is consistent with the
recognition that previously estimated rates for the 1990s had a positive
bias as a result of instrumental errors.. On average, the decadal
variability of the climate models with volcanic forcing now agrees
approximately with the observations, but the modelled multi-decadal
trends are smaller than observed. We add our observational estimate of
upper-ocean thermal expansion to other contributions to sea-level rise
and find that the sum of contributions from 1961 to 2003 is about 1.5
0.4 mm yr-) of 1.6 0.2 mm yr-1.
doi:10.1038/nature07080;
Received 27 December 2007;
RAPID
ROUNDUP:
Warming and rising of oceans (Nature) – experts react.
Professor Gary Meyers
is Director of the Integrated Marine Observing System at the University of
Tasmania.
“This paper is a landmark in our
understanding of change in the global oceans over the last several decades.
Using all of the historical data and different data-types and correcting their
inherent problems was a huge statistical challenge. The authors found a solution
that is both pragmatic and elegant.”
Professor Nathan Bindoff
is a physical oceanographer and Director of the Tasmanian Partnership for
Advanced Computing (TPAC). Partners include the University of Tasmania, CSIRO
Marine & Atmospheric Research and the Antarctic Climate and Ecosystems CRC. He
was a Coordinating Lead Author of the IPCC AR4 Working Group 1 chapter on
oceanic climate change and sea level observations (Chapter 5).
“This paper resolves a long standing problem in fully
understanding all of the contributions to sea-level rise. The contributions to
sea-level rise just simply didn’t add up from the 1950 to the 1990’s. This has
been a problem in the IPCC intergovernmental reports in 2001 and 2007. It could
have been either a measurement problem of the contributions from the ice sheets,
glaciers, or from the oceans, or the sea-level measurements themselves. This
paper provides an explanation for this problem, and uncovers the fact the oceans
have been absorbing more heat than we had previously understood. The absorption
of heat by the oceans is still the biggest contributor to sea-level, and what is
shown so beautifully in this paper is that we now have excellent agreement
between the effect of natural forcing on sea-level by volcanic eruptions such as
Pinatubo and changes in the ocean contribution to sea-level. I find it
remarkable, that the observations can now resolve the effects of volcanic
eruptions and just increases our confidence in using these corrected data for
understanding the climate change and its acceleration in the oceans. For
example, this work feeds into issues around the rate of sea-level rise by 2100
and whether there will be decreases in the oceans capacity to absorb carbon
dioxide.”
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