Claire Parkinson, now a senior climate change scientist at NASA, first began studying global warming's impact on Arctic sea ice in 1978, when she was a promising new researcher at the National Center for Atmospheric Research. Back then, what she and a colleague found was not only groundbreaking, it pretty accurately predicted what is happening now in the Arctic, as sea ice levels break record low after record low.

Parkinson's study, which was published in 1979, found that a doubling of atmospheric carbon dioxide from preindustrial levels would cause the Arctic to become ice-free in late summer months, probably by the middle of the 21st century. It hasn't been ice-free in more than 100,000 years.

Although carbon dioxide levels have not yet doubled, the ice is rapidly disappearing. This record melt confirms the outlook from Parkinson's 1979 model.

"It was one of these landmark papers," said Mark Serreze, director of the National Snow and Ice Data Center. "She was the first to put together the thermodynamic sea ice model."

What's more, collection of better data on sea ice over recent years has strengthened the models, making their predictions even more reliable—and disturbing.

The Intergovernmental Panel on Climate Change projects that if the world continues to emit greenhouse gasses at its current rate, carbon dioxide could double somewhere around the middle of the century. (Concentrations have increased from 280 parts per million during the preindustrial period to 405.25 as of December 2016.)

On a lower-emissions pathway, the world would get there closer to the beginning of the next century.

Either way, this doubling would cause roughly 2 degrees Celsius of global warming on average, but it would be much more dramatic at the poles. And whenever it happens, scientists expect it will bring on the disappearance of summer sea ice at the top of the Earth, which could have drastic consequences worldwide.

The Arctic's ice influences important systems, like ocean currents and the jet stream. As it disappears, the impacts worldwide could spread less like a ripple and more like a tidal wave.

The link between climate change and the dwindling Arctic ice pack is well established now, particularly after years of precipitous declines. January 2017 had the lowest levels of sea ice on historical record, and according to NASA, the ice is receding at a rate of 13.8 percent every decade. But in the 1970s, when Parkinson began her work, it was a novel concept. There was a growing understanding in scientific circles that the burning of fossil fuels was causing an increase in atmospheric CO2 in part thanks to the Keeling Curve, which was published in 1958. But average global temperatures had actually declined from the 1940s to the 1970s, as other forms of pollution counteracted the greenhouse effect.

"It was like, well maybe that expectation of warming was wrong," Parkinson said. Though many scientists agreed that increased carbon emissions would contribute to global warming, not everyone did. "Some people even started speculating we might go into another ice age," she said.

A graphic from Parkinson and Kellogg's 1979 study, showing an ice free Arctic in the summer.

While finishing up her dissertation at the National Center for Atmospheric Research (NCAR), Parkinson and climate scientist William Kellogg decided to take the theory about carbon dioxide emissions increasing global temperatures and apply it to a sea ice model that Parkinson had built. They took a conservative approach, associating a doubling of carbon dioxide emissions with 5 degrees Celsius of temperature rise in the Arctic. (They noted that others had suggested the Arctic could warm as much as 10 degrees Celsius.) Taking into account a number of variables that could accompany temperature rise, like changes to the atmosphere and oceans, they found that August and September would be ice-free in the Arctic with a doubling of CO2, which they wrote could happen by the middle of the 21st century.

In closing the article, they pointed to the larger issues: "Man's continued insertion of carbon dioxide into the atmosphere could cause dramatic climatic consequences worldwide and...the polar regions would respond in special ways," they wrote. Though the models they used were imperfect, and incapable of factoring in all potential influences, "the current models do suggest some grave consequences, and mankind would do well to proceed with caution where possible manipulation of the world's climate is at stake."

The latest Arctic Report Card issued by NOAA found that temperatures over land in the Arctic have risen 3.5 degrees Celsius since the beginning of the 20th century. But when Parkinson's results came out, they landed with a thud.

"Sadly, it was received by no one paying much attention," Parkinson said.

"When that paper came out it didn't get that much notice," Serreze said. "But then what you found was when we started to really advance in our climate models and how we build them, her work withstood the test of time."

Even though models and technology have advanced significantly, the paper is still cited from time to time.

Serreze, who began his career in 1982, said Parkinson's results—and the reality of what is happening now in the Arctic—would have been hard to believe then. "I just could never have imagined it," he said. "Over the course of my career, to see this happening to the Arctic? It's this eye-opener to me that climate change is not this far away thing—it's here and now."

Scientists were coming to the same conclusion that Parkinson and Kellogg did, including Exxon's own in-house scientists. NASA scientist James Hansen issued a stark warning to Congress in 1988. But it wasn't until 1999 that the concept of manmade global warming's impact on ice started to gain traction, Parkinson said.

That year, two studies were released that finally permeated the mainstream consciousness. The first, published by Parkinson and others at NASA, drew from roughly 20 years of satellite data and showed that the Arctic's ice was decreasing by an average of 2.8 percent each decade, and as much as 10.5 percent in some areas. (It's significantly higher now.) A few months later, another study was published by the University of Washington based on submarine observations that showed that the ice wasn't just shrinking—it was also becoming thinner.

Even though that's essentially what Parkinson and Kellogg had predicted in 1979, these two studies were based on observation, rather than a model, and came during an era of increased awareness of climate change. With their publication, suddenly the world recognized the threat that warming posed to the ice pack.

Since then, a number of scientists have made projections about when the Arctic would see its first ice-free summer. Serreze, for instance, has said it could come as early as 2030. Others have projected that it could happen as early as 2005 (it didn't) or as late as 2100.

In September 2016, a study looked at the accuracy of these predictions and found there's really no way to pinpoint the year. "The atmosphere is a chaotic system," said Alexandra Jahn, one of the authors of the study. "We have limits of the predictability. For climate, people are still starting to understand that we can't predict exactly what is going to happen."

The study, published in Geophysical Research Letters, found that any prediction of when the summer thawing might happen includes a 20-year period of uncertainty. That's because it's not known when, exactly, the doubling of CO2 will happen. What's easier to say, Jahn said, is that similar to what Parkinson wrote nearly 40 years ago, when a doubling happens, the formerly ice-encased Arctic will be dark blue and open in the warm months.

Despite all that, Parkinson said she maintains some optimism that mankind will head off the problem by reducing use of fossil fuels.

"To turn it around is not going to be easy," she said. "I'm not sure that the Arctic is doomed. I think it's still possible that the Arctic sea ice has a chance of rebounding a bit."