Two papers published today stress, once again, the urgency for world governments to take the goals set by the Paris Climate Agreement seriously. If emissions of greenhouse gases are not curbed and global temperatures are not kept below the agreed target, sea-level rise from Antarctic glaciers thawing might become unstoppable, models show.
The two models look at this issue from two different points of view. In the study led by Dr Tamsin Edwards of King's College London, published in Nature, the team modeled what would happen if we meet the ambitious Paris Agreement goal of keeping the global temperature increase to below 1.5°C (2.7°F) by 2100.
Meeting that target would halve the expected sea-level rise we could see by the end of the century, they found. Previous research has shown the average expected rise is 25 centimeters (9.8 inches), but Edwards and colleagues’ model, based on current pledges to curb emissions, reduces the increase to 13 centimeters (5.11 inches).
If the Paris Agreement goal becomes a reality it would also drastically reduce the melting of Greenland ice by 70 percent and the contribution of melting global glaciers to sea-level rise would be cut by 50 percent by 2100. Currently, almost all global glaciers are losing ice mass and this loss has been accelerating over the last few decades.
The second study, led by Dr Robert DeConto from the University of Massachusetts Amherst and also published in Nature, looked at both meeting the original Paris Agreement target of 2°C (3.6°F) or failing to fight the climate crisis altogether, leading to a 3°C (5.4°F) increase in the average global temperatures, the warming trajectory consistent with current fossil fuel emissions. In the former case, the melting will continue more or less as we are already seeing it. The meltwater from the Antarctic ice sheets will contribute between 6 and 11 centimeters (2.4 to 4.3 inches) to global sea-level rise.
This increase will put millions of people around the world in danger. But if these measures are not attempted, we are looking at an even worse situation. Without ambitious and serious interventions by 2060, the sea-level rise contribution from Antarctica alone would be up to 21 centimeters (8.2 inches) by 2100. If that happens, the ice-sheet collapse will become irreversible with glaciers continuing to retreat for centuries.
"If the world continues to warm, the huge glaciers on Antarctica might begin behaving like their smaller counterparts on Greenland, which would be disastrous in terms of sea-level rise," Dr DeConto said in a statement.
Long-term models become less precise as more factors can affect the outcome, but so far, scientists' sea-level projections for the early 21st century have proven accurate. This new model shows if we fail to tackle the climate crisis by 2060, the global sea level could be 10 meters (33 feet) higher by 2300.
The model even included the "optimistic" ability one day to geoengineer the planet or pull CO2 right out of the atmosphere. These interventions are currently theoretical but would result in a reduction – though not a cessation – of further sea-level rise so can't be relied upon, even if they existed, should we fail to meet the climate target.
So how are the world’s governments doing so far? The realistic answer is "poor but improving". According to the Climate Action Tracker, based on current policies we are looking at a global increase of 2.9°C (5.2°F) on average by 2100. If the pledges from the recent White House Climate Summit are respected that could take us down to a 2.4°C (4.3°F) rise, still in the danger zone but getting better.
The Paris Climate Agreement’s goals are ambitious but achievable; the actions we take today will affect our planet for centuries.