Not too late to save islands and low-lying areas from flooding

How high will sea levels have risen by the year 2300, and how much of this rise is already certain due to emissions this century? Researchers from the International Institute for Applied Systems Analysis (IIASA) recently published a study on this topic in Nature Climate Change, in collaboration with colleagues from the United Kingdom, Belgium, the Netherlands and Germany. Chris Smith, senior climate specialist at Vrije Universiteit Brussel (VUB), also contributed to this study. By isolating the effects of short- and medium-term emissions, the study establishes a direct link between today's policies and sea levels hundreds of years from now – an aspect that has not been quantified in this way before.

Research into sea level rise usually leads to projections up to the year 2100 based on a standard set of scenarios, but these do not allow us to distinguish the long-term consequences of current emissions. However, we must also consider these effects beyond 2100, because oceans and ice caps continue to respond for centuries," explains lead author Alexander Nauels. Nauels is a senior researcher in the Integrated Climate Impacts Research group of the IIASA Energy, Climate, and Environment programme. ‘Our study clearly shows that mitigation decisions in the coming decades will have consequences that extend over several centuries for coastlines worldwide.’

"We demonstrate that long-term, recorded sea level rise is closely linked to the peak level of global warming. It is therefore essential to limit the temperature increase as much as possible. We often say that every tenth of a degree counts: here, that translates into every tenth of a metre”, emphasises Chris Smith, senior climate specialist at Vrije Universiteit Brussel (VUB) and also co-author of the study. "For Belgium, this means an increased risk of flooding for large parts of Flanders."

The authors wanted to determine how much future sea level rise has already been determined by emissions from the past and the near future, and to show how strongly choices made in the coming decades will influence outcomes over centuries. "Those choices will determine when adaptation limits are reached and how many options coastal communities in vulnerable regions will still have," says co-author Aimée Slangen of the Royal Netherlands Institute for Sea Research (NIOZ).

‘The difference between decisive climate policy today and persistently high emissions is measured not only in degrees of warming, but also in metres of sea level rise that will reshape coastlines worldwide for centuries to come. It is important that we show that we still have the opportunity to limit the extent of sea level rise that we pass on to future generations,’ concludes Nauels.

The researchers discovered that current policies, taking into account emissions between 2020 and 2050, would lead to a sea level rise of approximately 0.3 metres by 2300. If emissions continue at the same rate until 2090, this would result in a global rise of approximately 0.8 metres. However, approximately 0.6 metres of this could be avoided if the world now implements the emission reductions in line with the Paris Agreement. These differences could determine whether some low-lying coastal areas and islands remain habitable.

“Our work highlights the lasting legacy of current emissions and shows that adaptation plans need to look centuries ahead,” says Matthew Palmer of the UK Met Office and co-author of the study. “We also show that some regions, such as the vulnerable islands in the Pacific, will experience even greater sea level rise than the global average. These regional and local changes need to be understood in much greater detail in order to better inform policymakers.”