Arctic melt has a dark side for the climate

It seems that a long held prediction of scientists about the consequences of a major Arctic ice melt has now been borne out by new research.

For more than 50 years, scientists have warned that if Arctic ice melts then the planet will be less able to reflect the sun’s energy and further fuel global warming.

Now, a new study using more than 30 years of satellite measurements has confirmed this hypothesis, warning that melting Arctic ice is having a greater impact on the world’s energy balance than previously thought.

The study, published in the US journal Proceedings of the National Academy of Sciences, is thought to be the first to accurately calculate how much extra energy the Earth has absorbed as Arctic ice melts.

Since the 1970s, the study says the Arctic has warmed by two degrees Celsius, more than double the global average, while the amount of ice left at the end of the melt season each September has dropped by 40 per cent.

Assistant Professor Ian Eisenman, one of three scientists at the Scripps Institution of Oceanography at the University of California, San Diego, who carried out the research told ABC News, “Our study showed the Arctic has darkened quite a bit during the past 35 years, and hence it’s absorbing a lot more solar radiation than it used to.

“If you take this extra energy that’s being absorbed in the Arctic and spread it out over the entire globe, we found that it’s 25 per cent as large as the heating that’s been caused by the direct effects of increasing CO₂ during the same period.

“This implies that Arctic sea ice retreat has been an important player in the global warming that we’ve observed during recent decades,” he told ABC News.

In the same way that white objects stay cooler than dark ones in the sun, the bright surface of Arctic ice has a high ‘albedo’ that helps keep the world cooler.

However, less ice means more areas of darker ocean exposed to the sun, which Professor Eisenman said then warmed the ocean.

However, Professor Eisenman said his other research suggested that Arctic ice was not yet at a stage where its disappearance during summer was irreversible.

The study used two sets of satellite observations of the Arctic to calculate the changes in the Earth’s albedo between 1979 and 2011.

The extra energy being absorbed was roughly double what some climate change computer models had predicted.

Australian scientists welcomed the study saying it will help refine future predictions of global warming.

Professor Steve Sherwood, director of the Climate Change Research Centre at the University of New South Wales, told ABC News, “So far attention has focused almost entirely on sea-ice coverage, but what really matters is the amount of sunlight reflected.

“This study provides a firm number for that, and its decrease over time.

“The main problem, which this study reiterates, is that sea ice keeps disappearing faster than models predicted.

“We knew that already, but this study verifies that this is indeed having the outsized effect on albedo that one would have expected.”

Professor Carlos Duarte, director of the Oceans Institute at The University of Western Australia, said the study was providing answers to “fundamental” questions.

He said while scientists had hypothesised that a loss of Arctic sea ice would have an impact on the Earth’s ability to reflect heat back to space, “the impact of these losses on planetary albedo had not been quantified to date.”

He added: “This study points again at the Arctic as a central, not marginal, region for the regulation of the climatic balance of Earth, where a tipping point is likely trespassed, with planetary-scale consequences.”