An Arctic heat wave ushered in the melt season two weeks earlier than average. This week a major fusion event is taking place in Greenland.
With temperatures of -6 degrees C, higher than normal in some areas, the southern part of the ice sheet is melting at its highest rate this season. Forecasts suggest that the melting in Greenland's South Dome, one of the highest elevations in the ice sheet, may be the strongest in early June since 1950.
Experts worry that Greenland may be bracing for another big thaw season.
Melting early this spring, low snow in some areas, and the potential for high pressure weather systems late this summer have raised red flags. Scientists are paying close attention after last summer's record ice loss, an event that scientists expect will occur more frequently as the Arctic continues to warm.
Scientists generally define the beginning of the melting season as the first three-day period in which melting is observed in at least 5% of the ice sheet. This year, that period began on May 13, almost two weeks earlier on average for the past several decades.
The meltdown coincided with a heat wave across much of the Arctic. Siberia and the central Arctic were some of the worst affected regions. But temperatures soared in parts of Greenland too, after a cold start to the month.
At the same time, the snow began to rapidly disappear along the fringes of the ice sheet, exposing bare rocks and ice. The lack of snow is one factor that increases the chance of an above-average thaw year, according to Jason Box, an ice expert with the Geological Survey of Denmark and Greenland.
Snow plays an important role in the Arctic. Its shiny surface helps reflect sunlight away from Earth. When the snow disappears, more heat can pass through and warm the surface. That, in turn, can cause a faster fusion.
Exposure to bare ice is happening earlier than usual this year, according to Box.
"Like last year, a shortage of snow along the western ice sheet preconditioned stronger-than-normal ice loss because seasonal snow protects dark bare ice with a shiny reflective covering," he told E&E. News by email. "So everything else is the same, we can expect more melt this year," he added.
Xavier Fettweis, a polar climate scientist at the University of Liege in Belgium, agreed that the lack of snow can pose a risk. He added that warm events are also necessary to start the feedback process.
The ice sheet is in the middle of you now. And the fact that it is melting at such high elevations, where snow cover tends to be heaviest, may be cause for some concern.
According to Fettweis, the melting at the South Dome, for example, is likely to make the snow wetter and denser. That will decrease its ability to reflect sunlight and absorb meltwater that forms on the surface of the ice sheet.
"Such an event so early in the season will certainly favor an above-average melt season this year," he told E&E News in an email.
More heat waves may be on the way.
According to Judah Cohen, director of seasonal forecasts at analytics firm Atmospheric and Environmental Research, the model's forecasts suggest strong high-pressure events over Greenland this summer. High pressure systems are often associated with warming of the ice sheet.
In fact, a recent study concluded that last summer's extreme melting was related to abnormally persistent high-pressure systems in Greenland (Climatewire, April 16). Greenland's melt rates last year were exceeded in 2012 alone, and the total amount of ice lost was actually the highest on record.
Forecasts this summer seem to suggest that high pressure systems will be more intense in July. And they can affect larger swaths of the ice sheet than the current melting event, which is mostly limited to the southern part of the ice sheet.
Cohen cautions that there is still considerable uncertainty about the forecasts so far in advance. It is too early, for now, to say whether these events will definitely occur.
But if the forecast is accurate, he said, "it definitely suggests high melting over the ice sheet."
Overall, he added, the forecast is in line with research indicating that these high-pressure systems are becoming more prevalent in Greenland. Some scientists believe that climate change, which can alter the structure and flow of the atmosphere, is partly to blame.
"Nothing is impossible; there is always variability, ”Cohen said of this summer's forecast. "But I think that only the background would support the continuation of this pattern of high pressure in and around Greenland."
None of this spring's events necessarily promise a melting season like last year. But taken together, with the threat of more heat events this summer, they suggest a reason for vigilance in Greenland this season.