The 2007 Intergovernmental Panel on Climate Change report was wrong, say a group of researchers, but not about whether there was global warming. Rather, the report underestimated its effects concerning ocean temperature and associated sea level increases between 1961 and 2003 - by 50 percent.
The report in the June 19 edition of Nature compared climate models with observations that show sea levels rose by 1.5 millimeters per year in the period from 1961-2003. That equates to an approximately 2 inch increase in ocean levels in a 42-year span.
Not exactly WaterWorld but not insignificant either.
The researchers say they corrected for small but systematic biases recently discovered in the global ocean observing system, and used statistical techniques that "infill" information in data-sparse regions.
They say their new results increase confidence in ocean observations and demonstrate that climate models simulate ocean temperature variability more realistically than previously thought.
"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," Lawrence Livermore National Laboratory climate scientist Peter 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.