The deep waters in the world’s oceans have not warmed in nearly a decade, according to a report by NASA, countering one theory for the hiatus in global warming.
Some climate scientists have tried to explain away the lack of global warming in the last 18 years by blaming oceans. The idea is that excess heat from burning fossil fuels has been trapped deep in the ocean depths, causing them to warm instead of the atmosphere.
But this theory seems to fall apart in the face of a new report by NASA’s Jet Propulsion Laboratory (JPL), which analyzes satellite and direct temperature data to conclude that the ocean’s depths — below 1.24 miles — have not warmed since 2005.
“The deep parts of the ocean are harder to measure,” said JPL’s William Llovel, the study’s lead author. “The combination of satellite and direct temperature data gives us a glimpse of how much sea level rise is due to deep warming. The answer is — not much.”
Ocean warming has also been a major explanation for rising sea levels because water expands as it warms. JPL study authors noted that sea levels are still rising, but ocean warming contributed almost nothing to this rise since 2005.
But while the ocean depths have cooled, the top layers of the ocean have been warming, which JPL says is an “unequivocal” sign of global warming. Recent studies have pointed to upper ocean warming — below 0.4 miles deep — as evidence of heat-trapping that is causing the planet to stay cooler than it otherwise would.
JPL’s Felix Landerer, who coauthored the deep ocean study, conducted a separate study looking at ocean warming in the Southern Hemisphere from 1970 to 2005, finding it absorbed up to 58 percent more heat than established by previous studies.
Oceanic warming is one of 52 explanations for why the world has not warmed in the last 18 years. Explanations for the lack of warming have ranged from increased volcanic activity to slower trade winds to Chinese coal plant emissions. Despite the wide range of explanations, natural oceanic cycles have been a dominant explanation for why the world stopped warming.
Many studies blamed the Pacific Ocean for trapping heat that stemmed warming, largely due to El Nino and La Nina periods. But a more recent study puts the blame squarely on the Atlantic Ocean for helping to cause the hiatus in warming.
A study by Professor Ka-Kit Tung from the University of Washington claimed global warming stopped because of “heat transported to deeper layers in the Atlantic and the southern oceans, initiated by a recurrent salinity anomaly in the subpolar North Atlantic.”
This oceanic cooling cycle “associated with the latter deeper heat-sequestration mechanism historically lasted 20 to 35 years,” according to Tung’s study. The study even suggests the hiatus in warming could last another decade.
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