Scientists are now saying that natural climate forces account for a “substantial” amount of the region’s warming in the past three decades.
A new study found that natural forces could account for as much as half of Arctic warming.
“Rapid Arctic warming and sea-ice reduction in the Arctic Ocean are widely attributed to anthropogenic climate change,” write climate scientists from the U.S., Australia and South Korea in a study that suggests that a “substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability.”
“Whenever you start to look at local climate trends, you have to look at the internal variability as well as the human-induced variability,” co-author Mike Wallace with the University of Washington told CTV News. “The natural variability is huge.”
Sea ice has declined 2.6 percent per decade on average since the late 1970s, reports CTV News, but the area north of Greenland and the Canadian archipelago has been warming more quickly due to rain and wind patterns in the South Pacific — not man-made carbon dioxide emissions.
“We find that the most prominent annual mean surface and tropospheric warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland,” the authors wrote. “In this region, much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic, namely, the North Atlantic Oscillation.”
But the researchers show that the increased warming is from a “negative trend in the North Atlantic Oscillation” is in response to “anomalous Rossby wave-train activity originating in the tropical Pacific.”
Wallace told CTV News that the increased warming in parts of the Arctic is due to unusually heavy rainfall in the South Pacific, which cause atmospheric turbulence around the globe.
“It induces what we call a planetary scale wave train,” Wallace said. “We can see exactly those kind of waves — like ship wakes — if we have the air flowing over an island and if we look down we can see in the cloud patterns exactly those kinds of wakes.”
The “wakes” Wallace talks about create waves throughout the atmosphere that warm the air by compressing it slightly. This in turn causes sea ice to melt in the Arctic.
“Think of Canada as downstream in that wake,” said Wallace. “If it happens to be in a ridge of that wave train, that translates into it being warmer than normal. That warmth comes from the prevalence of sinking motion in the atmosphere — it warms it by compressing it.”
The study does not call into question the foundations of climate science or the theory that man-made carbon dioxide emissions are warming the planet, but it does demonstrate that it can be hard to separate human-induced warming from natural systems.
“Unless global warming starts to accelerate at a rate far beyond what we’ve seen, it’s going to be a long time before weather statistics change so much from the human signal that it would become clearly detectable in the presence of natural variability,” Wallace said.
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