20 February 2018
The study, now published in the journal Nature Communications, analyzes the possible sea-level rises until 2300 within the constraints of the Paris Agreement. The researchers’ central projections indicate global sea-level rises between 0.7 m and 1.2 m until 2300 with Paris put fully into practice. As emissions in the second half of this century are already outlined by the Paris goals, variations in greenhouse gas emissions before 2050 will be the main determining factor for future sea levels. The researchers estimate that each five-year delay in peak global CO2 emissions will likely increase the median sea-level rise for 2300 by 20 cm.
“Man-made climate change has already preprogrammed a certain amount of sea-level rise for the coming centuries, so for some it might seem that our present actions might not make such a big difference – but our study illustrates how wrong this perception is,” explains lead author Matthias Mengel from the Potsdam Institute for Climate Impact Research (PIK). “Every delay in peaking emissions by five years between 2020 and 2035 could mean additional 20 cm of sea-level rise in the end – which is the same amount the world’s coasts have experienced since the beginning of the pre-industrial era.”
Global sea-level rise is driven by warming and expanding ocean water, as well as the melting of mountain glaciers, ice caps, and the vast Greenland and Antarctic ice sheets. These contributors respond in different ways and within different timescales to a warmer climate, ranging from centuries to millennia – a delayed response to today’s atmospheric warming. To analyze the sea-level rise under the Paris Agreement and the legacy of delayed mitigation, the scientists used a combined climate-sea-level model. They fed it with a set of scenarios of emission reductions in line with the Paris goals that span different reduction rates and emission peak years.
The model represents the sea-level contributors individually and can thus reflect their different responses to a warming world. The authors incorporate new scientific insights pointing to an Antarctic ice sheet very sensitive to atmospheric warming.
“Indeed, the uncertainty of future sea-level rise is at present dominated by the response of Antarctica. With present knowledge on ice sheet instability, large ice loss from Antarctica seems possible even under modest warming in line with the Paris agreement”, says Matthias Mengel. “Even a sea-level rise of up to three meters until 2300 cannot be ruled out completely, as we are not yet fully certain how the Antarctic ice sheet will respond to global warming.”
IIASA researcher Joeri Rogelj is a coauthor on the paper. He provided the international policy context and supported the design of scenarios for the modeling in line with the Paris Agreement.
“The Paris Agreement sketches a set of broad goals for future global climate action, like peaking global emissions as soon as possible, or limiting warming to well below 2°C,” says Rogelj. “These goals are important, because if we stay within the envelope of goals sketched by the Paris Agreement, future sea level rise will be limited significantly. At the same, these goals also allow for some wiggle room over the next couple of decades. Delaying a global peak in emissions over the next couple of decades will add to sea level rise, impacting people and populations in the centuries to come.”
Text adapted from a press release by Potsdam Institute for Climate Impact Research (PIK)
Mengel M, Nauels A, Rogelj J, Schleussner CF (2018). Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action. Nature Communications DOI: 10.1038/s41467-018-02985-8
Last edited: 23 February 2018
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