In summary, this is the outcome of two studies published this Wednesday in Nature. They can be seen as a shot ahead of the November climate summit in Glasgow. The aim of the summit is for the member states of the United Nations to tighten up their targets for reducing greenhouse gas emissions. If they achieve their current targets, warming would be 3°C. In 2015, the UN agreed in Paris to limit global warming to at least 2°C, and preferably 1.5°C. Many countries have already announced a tightening of the targets, but this has yet to be established within the UN.

All glaciers in the world

The two studies now published are pilot studies, but they differ in nature and design. One has simulated the contribution of all melting land ice to rising sea levels up to 2100, under different scenarios, and using a wide arsenal of climate and glacier models. This concerns all the glaciers in the world, and the large ice caps on Greenland and Antarctica. It is the most comprehensive model study of future sea level rise to date. The publication has 85 authors.

The other research has focused on the melting of the Antarctic ice sheet until 2300, based on one model. That is a very fine-grained model. It simulates the behavior of the ice sheet and the drifting ice shelves in the sea in different scenarios. “This is the best model of the Antarctic melt we have yet. They set the standard with this,” says Roderik van de Wal, who was not involved in this study, but who is one of the 85 authors of the other study. He is professor of sea level and influence on the coast at Utrecht University.

This is the best model of the Antarctic melt

Roderik van de Wal professor

The disadvantage of both studies is that they do not provide a picture of the total sea ​​level rise, but only of the melting land ice share, or of Antarctica. “That is indeed a bit confusing,” says Van de Wal. For example, the sea level also rises because the water heats up and expands as a result. This factor accounted for almost 40 percent of sea level rise between 2006 and 2015, according to the special report published by the IPCC, the UN climate agency, two years ago – Van de Wal was one of the lead authors. “You still have to convert our figures for the total sea level rise,” says Van de Wal.

The large study calculates, for example, that the contribution of land ice to sea level rise will halve in 2100 if warming does not come to 3°C, but 1.5°C. “It is clear that we will stay out of trouble in many places with that 1.5 degree warming,” says Van de Wal.

Varying Outcomes

The 85 authors do emphasize the uncertainty surrounding Antarctica in particular. The different models give very different results. In the pessimistic case, the contribution of Antarctica in 2100, even with a warming of 1.5°C, is already half a meter of sea level rise.

The other study shows a clear difference for Antarctica between a warming of 2 and 3°C. In the latter case, the melting of the ice sheet will accelerate abruptly around 2060. By 2300, Antarctica will cause a 1.5 meter rise in sea level. If you add the contributions from Greenland, all the other glaciers, and the expansion of the ocean water, you arrive at about 2.5 meters, according to Van de Wal.

That will be even more if greenhouse gas emissions do increase. Then Antarctica alone could cause a ten meter rise in sea level by 2300.

According to Van de Wal, the big question is whether we will limit warming to 1.5 or 2 degrees. Since the pre-industrial era, the earth has already warmed 1.1°C, and greenhouse gas emissions have only increased in recent decades. The corona pandemic has caused a downturn, but it is questionable whether this is temporary, now that economic activity is picking up again. Further warming will not stop until emissions are completely reduced to zero. Van de Wal: “I think we can be happy if we can still save that 2 degrees of warming.”