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Rising seas are irreversible on human time scales and among the most severe consequences of climate change. Emissions released in the coming decades will determine how much coastlines are reshaped for centuries to come. New research, published in Nature Climate Change, shows that near-term mitigation could spare future generations around 0.6 meters of sea-level rise, if we start lowering our carbon emissions according to the Paris Climate Agreement. This makes today’s decisions critical not only for limiting warming but also for coastal impacts. The study was conducted by researchers from the Austrian research intistute IIASA Royal NIOZ and Utrecht ľ�ϸ���Ӱ��.

goes beyond the usual sea level projections by quantifying how much sea-level rise in 2300 will be “locked in” by emissions this century. By isolating the effect of near- and mid-term emissions, the study provides a direct link between today’s policy choices and sea levels hundreds of years from now – an aspect that has not been quantified in this way before.

The long term legacy of greenhouse gas emissions

“It is common for researchers to make predictions about sea level rise in 2100 based on a standard set of emission scenarios,” explains lead author Alexander Nauels from IIASA. "But that doesn’t allow us to isolate the longer-term sea-level impacts of today’s greenhouse gas emissions.” Because oceans and ice sheets keep responding for centuries, we have to explore these impacts also on timescales beyond 2100. “Our study shows clearly that mitigation decisions on emissions in the next few decades will have multi-century consequences for coastlines worldwide.”

NIOZ researcher and co-author adds: 'Because sea levels vary greatly from place to place, we have also calculated what the sea level elevation will look like on a regional scale. In our study, we show how reducing greenhouse gas emissions in the coming decades will affect sea level rise in coastal areas worldwide.' The new research thus helps to better understand the effects of different policy choices on greenhouse gas emissions. The associated sea level rise determines the extent to which coastal areas can adapt to future changes.

Rapid reduction could make a difference of 0.6 metres

The researchers found that under current policies, emissions from 2020 until 2050 would already commit the world to about 0.3 meters of additional sea-level rise by 2300. This may seem like a modest increase, but it would have major implications for long-term adaptation planning for coastal areas. Extending emissions on this trajectory until 2090 would lock in a global rise of about 0.8 meters in 2300. The study shows that we could prevent roughly 0.6 meters of that rise, if the world started reducing emissions consistent with the Paris Agreement immediately. These differences can determine whether some low-lying coastal areas and islands, for example in the Pacific Ocean,  remain habitable or not. Co-author Tim Hermans, climate researcher at Utrecht ľ�ϸ���Ӱ��: “Reducing sea level rise is also important for the Netherlands, because it reduces the consequences of, for example, salt intrusion and the increasing risk of flooding.”

Lead author Nauels concludes: “The difference between continued high emissions today and a sharp reduction in emissions determines not only how many degrees the Earth will warm up, but also the extent of sea level rise, that will reshape coasts worldwide for centuries. We show that we still have the opportunity to limit the sea-level rise legacy we pass on to future generations.”