The central-western part of the Greenland ice sheet appears to be approaching a critical temperature threshold, according to a new study. The researchers have found early warning signals that this region of Greenland has already become unstable, and a tipping point may be soon lead to accelerated melting.
“We have found evidence that the central-western part of the Greenland ice sheet has been destabilizing and is now close to a critical transition,” said study lead author Niklas Boers of the Potsdam Institute for Climate Impact Research (PIK). “Our results suggest there will be substantially enhanced melting in the future – which is quite worrying.”
The overall stability of Greenland ice can be measured by the “melt-elevation feedback,” which is the interaction between surface elevation and surface melting. As the surface of the ice melts, it sinks into lower, warmer air in a vicious cycle that further accelerates melting.
“This mechanism is long known, and it is one of the prime suspects for the detected destabilization of the central-western parts of the Greenland ice sheet. But we cannot exclude that other feedbacks, for example related to the albedo of the ice sheet, play an important role too,” explained Boers.
In collaboration with study co-author Martin Rypdal from the Arctic University of Norway, Boers analyzed a combination of sea-level temperatures from weather stations, melt intensities from ice cores in central-west Greenland, and corresponding computer model simulations. The analysis revealed early warning signs in the fluctuations of ice sheet heights.
“The warning signs are caused by characteristic changes in the dynamics of the Greenland ice sheet, which reflect how well the ice sheet can resist against and recover from disruptions,” said Rypdal.
Previous modeling studies have shown that irreversible melting in Greenland is inevitable beyond a global average temperature rise of 0.8 to 3.2 degrees Celsius above pre-industrial levels. Once the threshold is crossed, the whole ice sheet could melt entirely over hundreds or thousands of years.
In addition to the reinforcing feedbacks that accelerate melting, there are negative feedbacks that could stabilize the Greenland ice sheet at intermediate heights levels, explained the study authors.
“We urgently need to better understand the interplay of the different positive and negative feedback mechanisms that determine the current stability and the future evolution of the ice sheet,” said Boers.
“The main problem is the so-called hysteresis. Regardless of the precise interplay of the different feedbacks, we would have to considerably reduce temperatures below pre-industrial to get back to the ice sheet height levels of the last centuries.”
“So practically, the current and near-future mass loss will be largely irreversible. That’s why it is high time we rapidly and substantially reduce greenhouse gas emissions from burning fossil fuels and re-stabilize the ice sheet and our climate.”
“Given the signs we detect in ice cores from the central-western part, we have to increase our efforts to gather more observation and to increase our understanding of the mechanisms at play, for more reliable estimates of the future evolution of the Greenland ice sheet,” said Rypdal.
The research is published in the Proceedings of the National Academy of Sciences.