More than one-third of Earth’s landmass is drained by rivers that seasonally freeze over. Ice transforms the hydrologic1,2, ecologic3,4, climatic5, and socio-economic6,7,8 functions of river corridors. Although river ice extent is declining in many regions of the world1, the seasonality, historical change, and predicted future changes in river ice extent and duration have not yet been quantified globally. Previous studies of river ice suggested that declines in extent and duration could be attributed to warming temperatures9,10, were based on data from sparse locations.

A massive glacier in Greenland – which is believed to have produced the iceberg that sank the Titanic – has become the fastest-flowing glacier in the world, according to a new study. The Jakobshavn Glacier is moving ice from the Greenland ice sheet into the ocean at a speed that appears to be the fastest ever recorded, researchers said.

“We are now seeing summer speeds more than 4 times what they were in the 1990s on a glacier which at that time was believed to be one of the fastest, if not the fastest, glaciers in Greenland. In the summer, the glacier reached a record speed of more than 17 km per year or over 46 m per day. These flow rates are unprecedented: they appear to be the fastest ever recorded for any glacier or ice stream in Greenland or Antarctica, the researchers said.

Furthermore, existing projections of future ice extent are based solely on the location of the 0-°C isotherm11. Here, using satellite observations, we show that the global extent of river ice is declining, and we project a mean decrease in seasonal ice duration of 6.10 ± 0.08 days per 1-°C increase in global mean surface air temperature. We tracked the extent of river ice using over 400,000 clear-sky Landsat images spanning and observed a mean decline of 2.5 percentage points globally in the past three decades.

To project future changes in river ice extent, we developed an observationally calibrated and validated model, based on temperature and season, which reduced the mean bias by 87 percent compared with the 0-degree-Celsius isotherm approach. We applied this model to future climate projections for 2080–2100: the average river ice duration declines by 16.7 days under Representative Concentration Pathway (RCP) 8.5, whereas under RCP 4.5 it declines on average by 7.3 days. Our results show that, globally, river ice is measurably declining and will continue to decline linearly with projected increases in surface air temperature towards the end of this century.

They noted that summer speeds are temporary, with the glacier flowing more slowly over the winter months. But even the annually averaged speedup over the past couple of years is nearly three times. This speedup means that the glacier is adding more and more ice to the ocean, contributing to sea-level rise. “We know that from 2000 to 2010 this glacier alone increased sea level by about 1 mm. With the additional speed, it likely will contribute a bit more than this over the next decade.

Jakobshavn glacier, which is widely believed to be the glacier that produced the large iceberg that sank the Titanic liner, drains the Greenland ice sheet into a deep ocean fjord on the coast of the island. At its calving front, where the glacier effectively ends as it breaks off into icebergs, some of the ice melts while the rest is pushed out, floating into the ocean. As the Arctic region warms, Greenland glaciers have been thinning and calving icebergs further and further inland.