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imagery shows that glaciers in the region were melting even faster in the 1930s than they are today

A brief cooling period starting in the mid-20th century allowed new ice to form, and then the melting began to accelerate again in the 2000s.

we now have a detailed historical analogue for more recent glacier loss

confirmed that glaciers are very sensitive indicators of climate."

cleaning up in the basement and had found some old glass plates with glaciers on them

The reason the plates were forgotten was that they were recorded for mapping, and once the map was produced they didn't have much value."

They contained aerial photographs of land, sea and glaciers in the southeast region of the country, along with travel photos of Rasmussen's team.

researchers digitized all the old images and used software to look for differences in the shape of the southeast Greenland coastline where the ice meets the Atlantic Ocean

calculated the distance the ice front moved in each time period.

Over the 80 years, two events stand out: glacial retreats from 1933-1934 and 2000-2010

1930s, fewer glaciers were melting than are today, and most of those that were melting were land-terminating glaciers, meaning that they did not contact the sea.

were melting retreated an average of 20 meters per year - the fastest retreating at 374 meters per year

Fifty-five percent of the glaciers in the study had similar or higher retreat rates during the 1930s than they do today.

more glaciers in southeast Greenland are retreating today, and the average ice loss is 50 meters per year. That's because a few glaciers with very fast melting rates - including one retreating at 887 meters per year - boost the overall average.

From 1943-1972, southeast Greenland cooled - probably due to sulfur pollution, which reflects sunlight away from the earth.

Sulfur dioxide is a poisonous gas produced by volcanoes and industrial processes. It has been tied to serious health problems and death, and is also the main ingredient in acid rain.

deadly pollution caused the climate to cool, but rather that the brief cooling allowed researchers to see how Greenland ice responded to the changing climate.

glaciers responded to the cooling more rapidly than researchers had seen in earlier studies

Sixty percent of the glaciers advanced during that time, while 12 percent were stationary

now that the warming has resumed, the glacial retreat is dominated by marine-terminating outlet glaciers, the melting of which contributes to sea level rise.

we see that the mid-century cooling stabilized the glaciers," Box said. "That suggests that if we want to stabilize today's accelerating ice loss, we need to see a little cooling of our own."