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CLIMATE
MODELS CONSISTENT WITH OCEAN WARMING
OBSERVATIONS Climate
models are reliable tools that help researchers better understand the
observed
record of ocean warming and variability. That's
the finding of a group of Livermore scientists, who in collaboration
with
colleagues at Scripps Institution of Oceanography, had earlier
established that
climate models can replicate the ocean warming observed during the
latter half
of the 20th century, and that most of this recent warming is caused by
human
activities. The
observational record also shows substantial variability in ocean heat
content
on interannual-to-decadal time scales. The new research by Using
13 numerical climate models, the researchers found that the apparent
discrepancies between modeled and observed variability can be explained
by
accounting for changes in observational coverage and instrumentation
and by
including the effects of volcanic eruptions. The
research, which will appear in the June 18 early online edition of the
journal
Proceedings of the National Academy of Sciences, casts doubt on recent
findings
that the top 700-meters of the global ocean cooled markedly from
2003-2005. “Our
analysis shows that the 2003-2005 'cooling' is largely an artifact of a
systematic change in the observing system,” said Krishna
AchutaRao, previously
of Livermore's Program for Climate Model Diagnosis and Intercomparison
(PCMDI),
now at the Indian Institute of Technology Delhi and the lead author of
the
paper. “The previous research was based on looking at the
combined ocean
temperature observations from several different instrument types, which
collectively appear to have a cooling effect. But if you look at the
observational instruments individually, there is no cooling.”
Observational
estimates of ocean heat content change in the 2005 World Ocean Atlas
are based
on millions of individual temperature measurements; however, they are
unevenly
distributed in space and time. In fact, until recently, many portions
of the
global ocean were very poorly sampled. To get a complete
four-dimensional
picture of global ocean temperatures, most researchers use statistical
methods
to “infill” missing observational data. Climate
models provide spatially complete ocean temperature data, so unlike the
incomplete observations, infilling is not required. By sampling the
models only
where there are observations, the The
research team also looked at the impacts of changes in ocean observing
systems.
A warm bias in the older instruments was recently discovered by
researchers in “This
transition from a measuring system biased warm to a more realistic one
appears
as a cooling. Obviously, models can't account for spurious variability
caused
by instrument changes,” AchutaRao said. ## This text
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