A sharp spike in Greenland temperatures since 1995 showed the giant northern island to be 1.5 C hotter than the 20th-century average, the warmest in more than 1,000 years, according to new ice core data.
Until now, Greenland’s ice cores — a glimpse of long-term temperatures before thermometers — had shown no clear signal of global warming on the island’s most remote northern central part, at least compared to the rest of the world.
But the ice cores also hadn’t been updated since 1995. Newly analyzed cores, drilled in 2011, show a dramatic increase in temperature over the past 15 years, according to a study this week in the journal Nature.
“We continue to (see) rising temperatures between the 1990s and 2011,” said lead author Maria Hoerhold, a glaciologist at the Alfred Wegener Institute in Germany. “We now have a clear signature of global warming.”
It takes years to analyze ice core data. Hoerhold has new cores from 2019, but has not finished studying them yet. She expects the temperature rise to continue as Greenland’s ice sheet and glaciers have been melting more rapidly lately.
“This is an important finding and confirms the suspicion that the ‘missing warming’ in the ice cores is due to the fact that the cores end before the strong warming begins,” said climate scientist Martin Stendel of the Danish Meteorological Institute, who was not part of of the research.
How Greenland’s temperature changed over time
The ice cores are used to create a graph of proxy temperatures for Greenland, running from the year 1000 to 2011. It shows temperatures slowly getting cooler over the first 800 years, then wobbling up and down as it warms to a sharp and sudden peak hotter from the 1990s onwards. One scientist compared it to a hockey stick, a description used for other long-term temperature data showing climate change.
The temperature increase after 1995 is so much greater than preindustrial times before the mid-1800s that there’s “almost zero” chance it’s anything but human-induced climate change, Hoerhold said.
The warming spike also reflects a sudden increase in the amount of water flowing away from Greenland’s melting ice, the study finds.
What had happened in Greenland is that natural weather variability, undulations due to an occasional weather system called Greenland lock, had historically masked human-induced climate change, Hoerhold said.
But about 25 years ago, warming got too big to hide, she said.
Previous data also showed that Greenland is not warming as fast as the rest of the Arctic, which is now warming four times faster than the global average. But the island seems to be catching up.
Why Greenland warmed more slowly than other parts of the Arctic
Ice core data for years showed that Greenland behaved a little differently than the Arctic, likely because of Greenland’s blockage, Hoerhold said. Other scientists said that as a giant landmass, Greenland was less affected by melting sea ice and other water factors compared to the rest of the Arctic, which is much more water-bound.
Hoerhold’s team drilled five new cores near old cores to match the established ice core records. They use the difference between two different types of oxygen isotopes found in the ice to calculate temperature, using an already established formula that is compared to observed data.
Hoerhold and outside scientists said the new warming data is bad news because Greenland’s ice sheet is melting. In fact, the study ends with data from 2011, and the following year saw a record melt in Greenland, and ice loss on the island has been high ever since, she said.
“We should be very concerned about the warming of northern Greenland, because that region has a dozen sleeping giants in the form of broad tidal glaciers and an ice stream,” said ice scientist Jason Box of the Danish Meteorological Institute. When he wakes up, this melting from Greenland will accelerate, he said.
And that means “rising seas that threaten homes, businesses, economies and communities,” said deputy chief scientist Twila Moon of the U.S. National Snow and Ice Data Center.