Under certain conditions, previously stable systems can become unstable: they tip. One example is the massive ice sheets on Greenland: if it becomes too warm, the ice melts, and there is also insufficient snowfall to form new ice. The ice sheet disappears permanently.
In this process, feedback loops occur that reinforce themselves once a certain state is reached, leading to a vicious cycle that can no longer be stopped, even while a significant amount of ice is still present. According to a recent study, the Greenland ice sheet may have now reached such a "tipping point". The rise in air temperature due to anthropogenic climate change leads to the melting of the ice sheet, which subsequently reduces its elevation. Its highest layers are thus exposed to lower, even warmer ambient air, where they continue to melt even faster - and so on. No one can halt an effect once it has started in this manner - the ice melts irreversibly.
Although counteracting effects do exist, such as higher humidity, which reduces solar radiation and can trigger snowfall - this also means more water vapour, which acts as a greenhouse gas and causes temperatures to rise. Such effects are no longer sufficient or are lost entirely: the "tipping point" has been crossed.
The study by the two researchers Niklas Boers of the Potsdam-Institut für Klimafolgenforschung (PIK) and the Freie Universität Berlin, and Martin Rypdal of the Arctic University of Norway, points to the tipping point having been reached for the West Greenland ice sheet. If it were to melt completely, global sea levels would rise by up to two metres within a century from this source alone, and by about seven metres in total. "We would probably need to bring global temperatures below pre-industrial levels to regain the previous elevation of the Greenland ice sheet," Niklas Boers told the Guardian.
Sources:
N. Boers, M. Rypdal: Critical slowing down suggests that the western Greenland Ice Sheet is close to a tipping point. PNAS, 2021. https://doi.org/10.1073/pnas.2024192118
https://www.theguardian.com/environment/2021/may/17/greenland-ice-sheet-on-brink-of-major-tipping-point-says-study
