Tuesday, March 2, 2010

Deep insight improves decadal predictions

Liz Kalaugher in Environmental Research Web covers some important modeling work: The fledgling field of predicting climate in the short term by using real data about the oceans in the initial conditions of a model has in some cases proved controversial. One paper in Nature by German scientists even led to a €2500 wager by members of the RealClimate team that Keenlyside et al's predictions of a pause in temperature rises due to natural internal variability would not prove correct. Although the bet was not taken up, the initial results are due in at the end of this year.

In the meantime, UK scientists have found that including data from the top 2000 metres of the ocean on both temperature and salinity, rather than just sea surface temperature as Keenlyside et al did, improves decadal predictions.

"Although the first attempts at initialized decadal climate prediction show some encouraging signs, there are also conflicting results," Doug Smith of the UK Met Office told environmentalresearchweb. "For example, Smith et al (2007) predict that at least half of the years after 2009 will exceed the warmest year currently on record, whereas Keenlyside et al (2008) suggest that natural variability will completely offset anthropogenic global warming until about 2020."

According to Smith, these two studies differ in the data used for initialization: Smith et al use sea surface temperature and sub-surface ocean temperature and salinity, whereas Keenlyside et al only use sea surface temperature. "Verifying decadal forecasts, and understanding the causes of these conflicting forecasts, is difficult because the observations, especially those beneath the ocean surface which are likely to be critical, are so sparse historically," said Smith.

Data from Argo floats, which can function to a depth of 2000 m, have only been available for the last decade or so. The project reached its goal of deploying 3000 probes in November 2007.

…Smith stresses that decadal predictions are still in their infancy, and further research is needed to assess their reliability. "In our study we assumed a complete knowledge of ocean temperature and salinity," he said. "This is not achievable in reality, even with the Argo array. We therefore plan to repeat our experiments but only using model temperature and salinity data at locations where we have real observations."…

Argo float aboard the the research vessel RV Thomas G. Thompson, photographed at its dock at the University of Washington, Seattle. Shot by Joe Mabel, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License

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