The world’s upper oceans may have stored far more heat from the warming climate than previously thought, according to a new study that purports to provide the first rough estimate of the amount of heat researchers have missed in their attempts to measure changes on the oceans’ heat content.
If the results hold up to additional scrutiny, they suggest that global warming’s effect on upper ocean temperatures between 1970 and 2004 has been underestimated by 24 to 58 percent, largely the result of sparse long-term measurements in the southern oceans, according to Paul Durack, the lead author of the study conducted by researchers at the Lawrence Livermore National Laboratory in Livermore, Calif., and NASA’s Jet Propulsion Laboratory in Pasadena.
Getting ocean heating right is important for estimating the amount of sea-level rise caused by the expansion of seawater as it warms and the amount attributed to melting of land-based glaciers and ice sheets, researchers say.
Ocean heat storage also influences estimates of how sensitive the climate system is to changes in greenhouse-gas levels, a key piece of the puzzle climate models must have to project possible trajectories for human-triggered climate change. Regionally, it influences the pace at which glaciers carrying ice from the world’s major land-based ice sheets on Greenland or Antarctica flow to the sea. Ice shelves along the coast, which act as breaks on the pace of ice loss from these outlet glaciers, melt from underneath as warm water wells up from depth and flows beneath the shelves.
Just as the oceans absorb a significant proportion of the carbon-dioxide humans add to the atmosphere, mainly through burning fossil fuels, the oceans take up about 90 percent of the heat attributed to this build-up of greenhouse gases. Southern-hemisphere oceans represent about 60 percent of the world’s oceans.
The notion that scientists have underestimated ocean warming isn’t new, noted Dr. Durack in a prepared statement. But this new study represents “the first time that scientists have tried to estimate how much heat we’ve missed,” he added.
The team used ocean-temperature measurements for the upper 2,300 feet of the oceans, satellite measurements of sea level, and the latest computer models to hunt for the missing heat. They based their hunt for the missing heat on the idea that sea water expands as it warms, raising global average sea levels.
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SOURCE: Christian Science Monitor