An increase in Pacific trade winds could have trapped heat in the ocean; the phenomenon could explain the surface warming "hiatus" that has taken place over the past 13 years.
The winds could have increased circulation in the ocean, which would have removed more heat from the atmosphere and caused colder water to be pushed up towards the surface, a University of New South Whales-Australia news release reported.
"Scientists have long suspected that extra ocean heat uptake has slowed the rise of global average temperatures, but the mechanism behind the hiatus remained unclear," Professor Matthew England, lead author of the study and a Chief Investigator at the ARC Centre of Excellence for Climate System Science at UNSW Australia, said in the news release. "But the heat uptake is by no means permanent: when the trade wind strength returns to normal - as it inevitably will - our research suggests heat will quickly accumulate in the atmosphere. So global temperatures look set to rise rapidly out of the hiatus, returning to the levels projected within as little as a decade."
The Pacific winds started getting stronger in the 1990s, and have continued to this day. Past climate models have not factored in stronger Pacific trade winds, which would explain why they did not capture the hiatus. Once the winds were included in the model it accurately depicted temperature observations.
"The winds lead to extra ocean heat uptake, which stalled warming of the atmosphere. Accounting for this wind intensification in model projections produces a hiatus in global warming that is in striking agreement with observations," Professor England said. "Unfortunately, however, when the hiatus ends, global warming looks set to be rapid.
The winds influence the ocean in a way that causes atmospheric heat to be stored in the Western Pacific Ocean waters, but it is not pushed very deep and could rise rapidly once the winds subside.
"Climate scientists have long understood that global average temperatures don't rise in a continual upward trajectory, instead warming in a series of abrupt steps in between periods with more-or-less steady temperatures. Our work helps explain how this occurs," Professor England said. "We should be very clear: the current hiatus offers no comfort - we are just seeing another pause in warming before the next inevitable rise in global temperatures."
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