Mass Loss From The Polar Ice Sheets Has Quadrupled
The ‘climate repair’ narrative that has been gaining traction recently
PICTURE COURTESY : PHYSICS WORLD
Mass loss from ice sheets in Greenland and Antarctica has quadrupled since the 1990s and now represents the dominant source of global mean sea-level rise from the cryosphere. This has raised concerns about their future stability and focused attention on the global mean temperature thresholds that might trigger more rapid retreat or even collapse, with renewed calls to meet the more ambitious target of the Paris Climate Agreement and limit warming to +1.5 °C above pre-industrial.
A new study led by Durham University in the UK synthesise multiple lines of evidence to show that +1.5 °C is too high and that even current climate forcing (+1.2 °C), if sustained, is likely to generate several metres of sea-level rise over the coming centuries, causing extensive loss and damage to coastal populations and challenging the implementation of adaptation measures.
Even the current level of global warming of 1.2°C, if sustained, is not safe, as the ice sheets are now losing around 370 billion tonnes of ice per year (four times more than in the 1990s) and this may still generate multiple meters of sea level rise over the coming centuries;
More research is needed to find the truly ‘safe’ level of temperature that would bring the ice sheets back into an equilibrium state and stop them contributing to sea level rise, but the authors hypothesize that it might be around or even lower than 1°C and closer to pre-industrial levels;
Polar ice sheets are melting significantly faster with each fraction of a degree of warming than they would recover were the global temperature to go down later in a ‘temporary overshoot’ scenario when the Paris targets of 1.5°C or “well below 2°C” are exceeded for a period of time. In other words, all the warming that does end up happening before humanity limits its influence on the climate – even if we then reverse it – still commits many generations to significant sea level rise caused by ice sheet melting.
To avoid this requires a global mean temperature that is cooler than present and which we hypothesise to be closer to +1 °C above pre-industrial, possibly even lower, but further work is urgently required to more precisely determine a ‘safe limit’ for ice sheets.
The study suggests that even global warming of 1.5°C, on the more ambitious end of the Paris Agreement target, would still likely generate several metres of sea level rise over the coming centuries due to significant mass loss from the polar ice sheets that is already occurring now and various feedback effects.
Lead author Professor Chris Stokes, in the Department of Geography at Durham University, said:- “Limiting warming to 1.5°C would be a major achievement and this should absolutely be our focus. However, even if this target is met or only temporarily exceeded, people need to be aware that sea level rise is likely to accelerate to rates that are very difficult to adapt to – rates of one centimetre per year are not out of the question within the lifetime of our young people.
The study presents a compelling argument that, when it comes to polar ice sheets, there really is no ‘safe’ level of additional warming ahead, so arguing about 1.5°C vs 2°C or any other target is counterproductive. Every extra fraction of a degree of warming adds extra centimeters of sea level rise on top of an already bad situation, endangering roughly 230 million people living on the coasts (within one meter of sea level) and multiple generations of their descendants.
It also shows, unfortunately, how far in trouble climate change has already got us with the polar ice sheets. The authors suggest that, at around 1°C of warming above pre-industrial level – already about 0.2°C lower than now – ice sheet melting would perhaps slow down to ‘manageable’ from an adaptation standpoint, but stopping them from contributing to sea level rise would likely require even lower temperatures (although more research is needed on this front);
The ‘climate repair’ narrative that has been gaining traction recently, which implies climate interventions such as geoengineering can ‘return’ the Earth to some previous healthy state, does not really account for these kinds of feedbacks and their century-scale consequences. Ice sheets are infinitely easier to melt than to regrow, and relying on some technological solution to lower the Earth’s temperature at some later point won’t bring them back and prevent sea level rise from causing extensive loss and damage or mass displacement.
The writer of this article is Dr. Seema Javed, an environmentalist & a communications professional in the field of climate and energy
