On the northwestern Greenland ice sheet, 2019 melt to-date is 1.2x that of the previous record melt in 2012.@PromiceGL
UPE_L site 72.9 N, 54.3 W, 209 m (686 ft) elevation pic.twitter.com/SU4KGyYQPf

— Prof. Jason Box (@climate_ice) July 31, 2019

That much melt won't happen right away. A recent study found that, if greenhouse gas emissions continue at current rates, it would still take a millennium for the ice sheet to melt entirely. That doesn't mean all of the consequences of today's melting will be delayed far into the future, however. The same study found the ice sheet would contribute as many as 63 inches to sea level rise in the next 200 years if emissions are not reduced, enough to flood Miami Beach, New Orleans and parts of New York and Boston, according to Grist.

And this summer's extreme melt could also have more immediate consequences. The fresh meltwater entering the North Atlantic could cause more storms in Northwest Europe, and the influx could raise global sea levels by more than one millimeter globally and two or more millimeters in the tropics, Geological Survey of Denmark and Greenland climatologist Jason Box told CNN.

"Whatever happens in Greenland radiates its impact down," Box said.

And what's happening in Greenland is unprecedented. Box told The Washington Post that two locations were recording more melt than in 2012. One, 75 miles east of the capital of Nuuk, had lost 8.33 feet of water as of Wednesday. The second, 497 miles north, had lost 7.38 feet, twice the average melt at that location over the last ten years.

Greenland's ice sheet measured its record surface temperature Wednesday and its record melt rate Thursday, losing 12.5 gigatons of ice, University of Liège polar scientist Xavier Fettweis tweeted.

Yesterday was the warmest day in recorded history on the Greenland ice sheet.

Today is its biggest melt day. More than 12 billion tons of water will have entered the ocean by tonight, permanently raising sea levels.

We are in a climate emergency.https://t.co/WUL0v2CW8O https://t.co/FnGMFZ1IsC

— Eric Holthaus (@EricHolthaus) August 1, 2019

Polar researchers have posted some dramatic images of the heat wave on social media. Climate scientist Irina Overeem shared a video of meltwater rushing past a monitoring station she placed in Western Greenland eight years ago, as meteorologist Eric Holthaus reported for RollingStone.

"With the exceptional heat wave coming I have my fingers crossed for it not being washed away," she tweeted.

The Naujatkuat River in West Greenland running high in end of July, my gauging station is perched on the bedrock. With the exceptional heat wave coming I have my fingers crossed for it not being washed away. pic.twitter.com/JPofxDIELN

— Irina Overeem (@IrinaOvereem) July 30, 2019

Meanwhile, researchers at Zackenberg Research Station in Northeast Greenland posted a photo of themselves in shorts, as temperatures passed a balmy 19 degrees Celsius Wednesday.

The recent #Greenland #heatwave has been felt most in the NE where very few peole live and we have very few observations, however the research station at Zackenberg is an exception - imporessive temperatures here! https://t.co/3wX2oIO5dx

— Greenland (@greenlandicesmb) August 1, 2019

The heat and melting in Greenland is a frightening sign of the climate crisis: Ice core samples show that melt days like those seen this week occurred very rarely in the past thousand years, but global warming caused by the burning of fossil fuels is making them more likely, Holthaus wrote.

"This melt event is a good alarm signal that we urgently need change our way of living," Fettweis told Holthaus.

But if we do change, there is still hope we can stop the worst from happening. Scientists say melt in Greenland won't become irreversible until global temperatures reach 1.5 to two degrees Celsius above pre-industrial levels.

"That means whether or not Greenland's ice sheet melts completely is almost entirely in human control: A full-scale mobilization ­— including rapidly transforming the basis of the global economy toward a future where fossil fuels are no longer used — would probably be enough to keep most of the remaining ice frozen, where it belongs," Holthaus concluded.