The Guardian reports:

The Greenland ice cap is losing an average of 30m tonnes of ice an hour due to the climate crisis, a study has revealed, which is 20% more than was previously thought.

Some scientists are concerned that this additional source of freshwater pouring into the north Atlantic might mean a collapse of the ocean currents called the Atlantic meridional overturning circulation (Amoc) is closer to being triggered, with severe consequences for humanity.

Major ice loss from Greenland as a result of global heating has been recorded for decades. The techniques employed to date, such as measuring the height of the ice sheet or its weight via gravity data, are good at determining the losses that end up in the ocean and drive up sea level.

However, they cannot account for the retreat of glaciers that already lie mostly below sea level in the narrow fjords around the island. In the study, satellite photos were analysed by scientists to determine the end position of Greenland’s many glaciers every month from 1985 to 2022. This showed large and widespread shortening and in total amounted to a trillion tonnes of lost ice.

“The changes around Greenland are tremendous and they’re happening everywhere – almost every glacier has retreated over the past few decades,” said Dr Chad Greene, at Nasa’s Jet Propulsion Laboratory in the US, who led the research. “It makes sense that if you dump freshwater on to the north Atlantic Ocean, then you certainly get a weakening of the Amoc, though I don’t have an intuition for how much weakening.”

The Amoc was already known to be at its weakest in 1,600 years and in 2021 researchers spotted warning signs of a tipping point. A recent study suggested the collapse could happen as soon as 2025 in the worst-case scenario. A significant part of the Greenland ice sheet itself is also thought by scientists to be close to a tipping point of irreversible melting, with ice equivalent to 1-2 metres of sea level rise probably already expected. [Continue reading…]