This is an aerial view of a lake on the Greenland Ice Sheet before, left, and after drainage, right. (Thomas R. Chudley)

December 2

A cerulean lake consisting of glacial meltwater on the surface of the Greenland ice sheet, located about 18 miles from where the Store Glacier meets the sea in west Greenland, briefly became one of the world’s tallest waterfalls during the course of five hours in July 2018.

The waterfall, like many others on the ice sheet’s surface, was triggered by cracks in the ice sheet. In the case of this one meltwater lake that scientists closely observed in July 2018, the water cascaded more than 3,200 feet to the underbelly of the glacier, where the ice meets bedrock. There, the water can help lubricate the base of the ice sheet, helping the ice move faster toward the sea.

The observations of scientists, armed with aerial drones and other high-tech equipment, of the partial lake drainage that resulted could help researchers better understand how surface melting of the ice sheet could affect its melt rate, and improve global sea level rise projections.

Sea levels are rising more than expected, according to scientists

Sea levels are rising more than expected, according to scientists

Credit: Florian Ledoux

Sea levels rose 10 meters above present levels during Earth’s last warm period 125,000 years ago, according to new research that offers a glimpse of what may happen under our current climate change trajectory.

Our paper, published today in Nature Communications, shows that melting ice from Antarctica was the main driver of sea-level rise in the last interglacial period, which lasted about 10,000 years.

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Rising sea levels are one of the biggest challenges to humanity posed by climate change, and sound predictions are crucial if we are to adapt.

This research shows that Antarctica, long thought to be the “sleeping giant” of sea-level rise, is actually a key player. Its ice sheets can change quickly, and in ways that could have huge implications for coastal communities and infrastructure in the future.

Aerial footage showing the devastation caused by severe storms at Collaroy on Sydney’s northern beaches in June 2016. UNSW Water Research Laboratory

A warning from the past

Earth’s cycles consist of both cold glacial periods – or ice ages – when large parts of the world are covered in large ice sheets, and warmer interglacial periods when the ice thaws and sea levels rise.

The Earth is presently in an interglacial period which began about 10,000 years ago. But greenhouse gas emissions over the past 200 years have caused climate changes that are faster and more extreme than experienced during the last interglacial. This means past rates of sea-level rise provide only low-end predictions of what might happen in the future.

We examined data from the last interglacial, which occurred 125,000 to 118,000 years ago. Temperatures were up to 1℃ higher than today – similar to those projected for the near future.

Our research reveals that ice melt in the last interglacial period caused global seas to rise about 10 meters above the present level. The ice melted first in Antarctica, then a few thousand years later in Greenland.

Sea levels rose at up to 3 meters per century, far exceeding the roughly 0.3-meter rise observed over the past 150 years.

The early ice loss in Antarctica occurred when the Southern Ocean warmed at the start of the interglacial. This meltwater changed the way Earth’s oceans circulated, which caused warming in the northern polar region and triggered ice melt in Greenland.