Natural variations in the Arctic climate “may be responsible for about 30–50 percent of the overall decline in September sea ice since 1979,” the U.S.-based team of scientists wrote in the journal Nature Climate Change.

Sea ice has shrunk steadily and hit a record low in September 2012 — late summer in the Arctic — in satellite records dating back to 1979.

The ice is now around the smallest for mid-March, rivaling winter lows set in 2016 and 2015.

The study, separating man-made from natural influences in the Arctic atmospheric circulation, said that a decades-long natural warming of the Arctic climate might be tied to shifts as far away as the tropical Pacific Ocean.