Greenland ice sheet melting at an accelerating rate due to global warming

By Philip Guelpa
14 December 2018

A newly published article in the journal Nature (“Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming,” Trusel et al., 6 December 2018) reports finding that runoff from the Greenland ice sheet (GrIS) is accelerating as a result of global warming. The consequences for both sea-level rise and climate change are severe.

Using stratigraphic data from ice cores extending deep into the center of the ice sheet, which document changes in melting and refreezing over time, the researchers found a very high statistical correlation (P<0.01, less than 1 percent probability that the correlation is due to chance) between the ice core data, data from modern satellite observation, air temperature records, and computer modeling of melt rates. By comparing the annual thickness of layers of refrozen meltwater within the ice, as documented in the cores, with modern records, the researchers could extrapolate backwards to reconstruct the annual rate of melting during the period represented in the cores. This method is roughly analogous to the study of past climates using tree rings.

Scientists stand on the edge of a crevasse formed by meltwater flowing across the top of the Greenland Ice Sheet during a WHOI-led expedition in 2007. Credit: Photo by Sarah Das, Woods Hole Oceanographic Institution

Their conclusion is that “the magnitude of recent GrIS melting is exceptional over at least the last 350 years.” And further, that “the initiation of increases in GrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability.” In other words, human-induced global warming is causing the ice sheet to melt at an unprecedented and increasing rate, at least during the period documented in the cores.

The analysis found “a pronounced 250% to 575% increase in melt intensity over the last 20 years, relative to a pre-industrial baseline period (eighteenth century),” based on two separate cores. “Furthermore, the most recent decade contained in the cores (2004-2013) experienced a more sustained and greater magnitude of melt than any other 10-year period in the ice-core records.” In one of the cores, 2012 was the strongest melt season on record.

Ominously, the data indicate that the correlation between the rise in air temperature and the rate of melting is “nonlinear”—the latter is increasing faster than the former. Consequently, in the future “continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions”—i.e., the flow of melted water from the icecap into the ocean.

Accelerating rates of ice sheet melting coincide with pronounced decreases in Arctic sea ice, both indications of warming climate. The greater expanses of open water in the Arctic Ocean cause increased absorption of solar radiation (dark water absorbs more heat than white ice), leading to warming of the water and even greater melting of sea ice, resulting in warming of the overlying air. The authors suggest a consequent acceleration of ice sheet melting due to increased air temperatures. This, in turn, causes reduced reflectivity (decreased albedo) and greater solar absorption on the ice sheet’s surface due to puddled meltwater. Together, these processes constitute a vicious circle, increasing the rate of melting on both land and sea. Quantitative changes are rapidly being transformed into qualitative ones, which may soon become irreversible.

The increased flow of fresh water into the North Atlantic as well as the decrease in Arctic sea ice are likely to be at least contributing causes of shifting ocean circulation, known as the summer North Atlantic Oscillation, with potentially dramatic consequences for regional climate. One effect could be the southward deflection of the Gulf Stream. The reduction in warm water flow northward and eastward could, ironically, result in a decrease in temperatures in northeastern North America and Europe, with negative effects such as shorter growing seasons.

Similar recent increases in the rate of ice melting have been documented in Antarctica.

The consequences of sea level rise alone, given the huge amount of water currently stored in the Antarctic and Greenland ice sheets, the two largest reservoirs of frozen water on the planet, would be devastating. Eight of the world’s 10 largest metropolitan areas—Tokyo, Mumbai, New York City, Shanghai, Lagos, Los Angeles, Calcutta, and Buenos Aires—and up to half of the world’s population are vulnerable to sea level rise. Estimates vary widely, depending on a variety of scenarios, but sea levels could potentially increase by several meters in the foreseeable future. The displacement of hundreds of millions of people would dwarf the scale of anything previously experienced. Ultimately, if all the world’s ice sheets were to melt, sea levels could rise on the order of 65 meters (over 200 feet), inundating vast expanses of currently inhabited land.

The data collected from the Greenland ice cores objectively demonstrate the reality of accelerating global warming during the industrial period. Coming shortly after the dire warnings made by the UN Intergovernmental Panel on Climate Change, and starkly illustrated by the growing intensity of hurricanes and wild fires around the world in recent years, this study reinforces the overwhelming scientific understanding that climate change is an immediate threat to human civilization.

The feeble and ineffectual measures so far attempted by the bourgeoisie to address climate change do not begin to meet the scale of the problem. The division of the world into rival nation states and the imperious drive to maximize profit under capitalism preclude the level of effort that is required. Only a unified worldwide marshalling of resources, guided by socialist policies, can avert the otherwise inevitable catastrophe.

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