Greenland, despite what the name might suggest, is topped by an ice sheet that covers 90 percent of its surface area. At its thickest, this ice is two miles deep and at its highest is over two miles above sea level.
During July, 97 percent of this ice sheet experienced melt — meaning that 97 percent of the surface area had experienced some form of snow or ice melt, not that 97 percent of the total had melted.
“There’s enough ice in Greenland to raise global sea level by 7 meters. If we had 97 percent of the ice sheet melt away, there’d be a lot of coastal areas that’d be underwater right now,” said Tom Mote, professor and department head of geography at the University.
On a typical summer day, around 25 percent of the ice sheet sees melt. Temperatures this summer led to some remarkable conditions, Mote said. Scientists recorded that 40 percent of the sheet’s surface was getting melt when a ridge of warm air stagnated over Greenland — the catalyst for the big melt.
Mote became aware of the melt when a Rutgers University colleague called from the coast of Greenland. She was working near Kangerlussuaq, towards the southwestern tip of the island, when a 60-year-old bridge over the Watson River washed out because of floods caused by the massive melt.
Mote, who normally waits to review the melt data until the end of the season, contacted associates at NASA. Mary Albert, a professor at Dartmouth, joined the conversation by satellite conference from the summit of the ice sheet. She reported visual confirmation that there was melt even at the highest elevation.
“We haven’t seen any other summer that’s produced as much melt through the end of September as we’ve already seen in early August," Mote said. "Granted, we don’t see much in September anyway, so if you’re going to break it, you’re probably going to break it in August. The entire summer has been really remarkable."
Mote has produced a visual representation of the ice melt this year from January through July (image to the left). The colors with hatch marks represent melt: note the flair on July 11 and 12, the peak of the melt for this season so far.
Scientists estimate that the last time a melt occurred on this scale was in 1889, based on ice samples.
“You can drill into the ice, and you can look at it just like looking at tree rings and count back in time. We think the last time this occurred was 1889, and prior to that we think the last time this occurred was 680 years before,” Mote said.
While scientists have seen more melts at higher temperatures during the past few decades, Mote emphasized that this melt was just one event.
“And that’s the way I would describe it: a very unusual weather event that caused really extensive melt embedded within this changing climate over Greenland that has led to more frequent and intense melting along the edge of the ice sheet,” he said
More frequent and intense melting has led to other changes besides coastal floods like the one seen on the Watson River.
Moulins are glacial lakes. As ice melts, these lakes can fill and empty in the course of hours. Marco Tedesco of the City University of New York is another colleague of Mote’s. He made a video documenting one of these moulins. As temperatures warm, the formation of these lakes becomes more frequent.
Mote has been studying the ice sheet since the 1990s. His attention in that area waned when there seemed to be no general interest and there were few comparable data sources. With the introduction of new satellite technology and global interest in climate change, Mote has picked up the research again over the last five to 10 years.
“We’ve had some really remarkable things going on over the ice sheet that have attracted a lot of interest in this again,” Mote said.
No comments:
Post a Comment