Earth's ocean surface has been hotter in 2014 than any previous year on record, according to a new analysis by scientists at the University of Hawaii-Manoa. This suggests the recent slowdown in Earth's long-term temperature rise — sometimes called a "hiatus" — may be coming to an ominous end.
The planet has been warming dangerously for decades, but since 2000 the rise of global sea-surface temperatures has slowed, even as greenhouse gas emissions have continued to accumulate in the atmosphere. Climate scientists long struggled to locate this "missing heat," although many said it had likely cycled into deeper waters. The sea surface already absorbs 93 percent of all heat from global warming, and researchers have recently found evidence that much of this excess heat did move to lower depths in both the Atlantic and Pacific, churning down into middle layers but not the abyss.
Average sea-surface temperature rise began speeding up again in April 2014, according to Hawaii-Manoa climate scientist Axel Timmerman, and in July it hit uncharted territory. Global surface waters reached 0.55 degrees Celsius above the long-term average, beating the record of 0.51 degrees set in 1998. In the especially hot North Pacific, surface waters were about 0.8 degrees above average.
"The 2014 global ocean warming is mostly due to the North Pacific, which has warmed far beyond any recorded value," Timmerman says in a statement. This extreme Pacific warming, he adds, "has shifted hurricane tracks, weakened trade winds and produced coral bleaching in the Hawaiian Islands."
This Pacific heating has occurred despite the conspicuous absence of El Niño, which had been expected to develop this year (and may still). But the surge of warm water has nonetheless created some El Niño-like effects, including more tropical cyclones in the Pacific and drier conditions in Australia. It has also led to severe bleaching of some coral reefs around Hawaii, a phenomenon that occurs when unusually warm seawater forces coral to expel its symbiotic algae, turning the reefs a ghostly white.
Why are things heating up so quickly in 2014? The answer may still be a bit murky, but Timmerman says a shift in summer trade winds played a key role, allowing nearly a decade's worth of stored heat to escape from the tropical Western Pacific. "Record-breaking greenhouse gas concentrations and anomalously weak North Pacific summer trade winds, which usually cool the ocean surface, have contributed further to the rise in sea surface temperatures," Timmerman says. "The warm temperatures now extend in a wide swath from just north of Papua New Guinea to the Gulf of Alaska."
These record-breaking temperatures indicate the 14-year-long pause in ocean warming has come to an end, Timmerman adds. And in addition to a warmer ocean surface, recently released data from American and Japanese scientists suggest last month was the warmest October on record for Earth overall, putting 2014 on pace to vie for the warmest year in recorded history.
For more about the fight to document and prevent coral bleaching in Hawaii, check out this video by the Hawaii Department of Natural Resources and the Australia-based Catlin Seaview Survey:
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