The first recorded summer that melts virtually all of the Arctic’s floating sea ice could occur as early as the 2000s, according to a new scientific study about a decade earlier than researchers previously predicted.
The peer-reviewed findings, released on Tuesday, also show that this climate change milestone could materialize even if nations succeed in cutting greenhouse gas emissions more decisively than they are currently doing. Previous projections had found that stronger action to slow global warming might be enough to preserve summer ice. The latest research suggests that, with regards to Arctic sea ice, only drastic reductions in emissions may be able to reverse the effects of the warming already underway.
We’re about to lose summer sea ice cover in the Arctic very quickly, basically regardless of what we’re doing, said Dirk Notz, a climate scientist at the University of Hamburg in Germany and one of the five authors of the new study. We’ve waited too long now to do anything about climate change to protect any remaining ice any longer.
As sea ice has shrunk in recent decades, communities, ecosystems and economies around the world have been grappling with the consequences. But the effects extend well beyond the region.
Sea ice reflects solar radiation back into space, so the less ice there is, the faster the Arctic warms. This causes the Greenland ice sheet to melt more quickly, adding to global sea level rise.
The temperature difference between the North Pole and the Equator also affects storm tracks and wind speeds in the mid-latitudes, meaning that Arctic warming could affect weather events such as extreme rainfall and heat waves in the temperate North America, Europe and Asia.
Over the past four decades, the Far North has already warmed four times faster than the global average, a phenomenon scientists call Arctic amplification.
Our result suggests that Arctic amplification will come faster and stronger, said Seung-Ki Min, a climate scientist at Pohang University of Science and Technology in South Korea and another author of the new paper. This means that related impacts will also come faster.
Over the course of each year, the surface water of the Arctic Ocean freezes and melts with the seasons. The amount of ice grows in the winter, peaks around March, then decreases toward an annual low, typically in September.
The September lows have been declining since continuous satellite measurements began in 1979, leading researchers to try to predict when the ocean might experience its first summer that will effectively melt all floating ice.
That doesn’t mean there won’t be ice on the water, but patches of ice are expected to remain in some corners of the Arctic for some time to come. Instead, the threshold scientists use is 1 million square kilometers of ice, or about 386,000 square miles. This is less than 15% of the Arctic seasonal minimum ice cover in the late 1970s.
By looking at both satellite measurements of ice cover and computer models of global climate, the researchers predicted that September ice will likely drop below this level for the first time before 2050. But the exact timing has been difficult to pin down. predict, in part because computer models generally underestimate the sea ice decline that satellites have detected.
The authors of the latest study, which was published in the journal Nature Communications, accounted for this problem by first adjusting climate models to align more closely with satellite observations. They then used the fitted models to project future sea ice changes under four possible scenarios for greenhouse gas emissions over the next few decades.
In three of these scenarios, representing moderate to large increases in emissions, September ice falls below the critical threshold for the first time as early as the 2000s, about a decade earlier than previously estimated.
But the study also found roughly similar times in the fourth scenario, in which humanity will stop pumping further heat-trapping gases into the atmosphere around 2070, something nations’ policies are not on track to achieve. Previous research has suggested that September could remain heavily frozen under this scenario.
The unfrozen September 1 of the Arctic oceans, if and when it arrives, will be a major scientific landmark, but it won’t be something of a game changer, said Mark C. Serreze, director of the National Snow and Ice Data Center at the University of Masso Colorado. The Arctic began turning into a bluer ocean decades ago, initiating vast changes to polar bear populations, shipping lanes, access to natural resources, and geopolitics.
It’s already happening, said Dr. Serreze, who was not involved in the new research. And as the Arctic continues to lose its ice, those impacts are going to get bigger and bigger and bigger.
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