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Just days before Christmas in 2016, the North Pole was 50 degrees above its usual winter temperature. The top of the world was just above freezing.

Unusually warm air had smothered the Arctic throughout that year, and now a recently published report, led by government scientists at the National Oceanic and Atmospheric Administration (NOAA), found that it's nearly impossible to explain the intensity of this warmth simply by normal fluctuations in weather.

A heating event like this isn't natural, they argue -- it's largely human-induced, specifically by the greenhouse gases emitted by human industry and trapped in the atmosphere.

Scientists have long predicted that the Arctic would show extreme, amplified consequences of these emissions, particularly as sea ice melts and plummets in size.

“It’s been said the Arctic is the canary in the coal mine,” NOAA meteorologist and study co-author Martin Hoerling said in a statement. “The canary in the coal mine really chirped loudly in 2016. This is where the signal is clearly emerging beyond the noise, and it affirms predictions of how climate change will unfold on Earth.”

The research team was able to show that back in the late 1800s, when greenhouse gas emissions were considerably lower than they are today, such abnormal Arctic heat waves would have a "near zero" chance of occurring, Lantao Sun, an NOAA atmospheric scientist and lead author of the study, said in an email. 

To show this, the research team plugged actual measurements, including greenhouse gases, sea-surface temperatures, and sea ice concentrations, into a widely-used computer model to see if it accurately reproduced the 2016 warming event in the Arctic -- which it did.

Then, they turned greenhouse gas emissions and temperatures down to their late-1800s levels -- back when the Earth was cooler and greenhouse gas emissions were considerably less.

After running this 19th-century experiment 30 times, they found that without those climate change indicators, "the Arctic is considerably colder than what we observed recently and there is near-zero probability for the Arctic surface temperature to be as warm as in 2016," said Sun.

Similar warming events in the Arctic have now occurred every winter for the past three years, "which is what we expect under warming conditions," Walt Meier, a senior research scientist at the National Snow and Ice Data Center, said in an interview.

"Three years in a row is something you take notice of -- that's something unusual," Meier, who had no involvement in the study, said.

But, cautions Meier, saying that a particular warming event is a human-induced climate effect, rather than inherently fickle weather, is tricky to do with the limited data we have. Reliable temperature monitoring in the hard-to-reach Arctic doesn't go back that far, only to the early 1980s.

"With warming trends we're just kind of rolling the dice -- we can still get odd things that can happen," he said.

"It's like rolling double sixes two times in a row -- it does happen," said Meier. "But if it starts happening four times in row or eight out of 10 times you’re going to become suspicious."

"And we’re getting to that."

Even so, less sea ice -- which is at its lowest point in the last 1,500 years in the Arctic -- means more heat waves to come.

Sea ice acts as a formidable "bulwark" to storms carrying heat and moisture into the Arctic, often breaking the storms apart, said Meier.

And with less ice, comes less protection.

"I think we should expect to see more frequent heat waves in the Arctic, particularly in the winter, due to less sea ice allowing the storms to more easily track into the Arctic," said Meier.

Sun said we should "absolutely" expect to see more warming in the Arctic, noting that the study found that 60 to 70 percent of the 2016 Arctic warming can be attributed to the loss of sea ice. The rest was caused by natural intrusions of warm air into the Arctic, including contributions from El Niño.

Arctic weather in 2016 may have often been abnormal or anomalous, but to many scientists, it's becoming all too common.

"It is not only astonishing to see how large the warm anomaly in the Arctic is from day to day compared with other regions on Earth," Jason Briner, who researches global climate change at the University of Buffalo and had no involvement in the research, said in an email.

"It is also remarkable how persistent the extreme warm weather is in the Arctic. In fact, the warm weather events are so persistent that we can no longer call it weather, but we have no choice but to call it a new climate state."

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