Failure to meet the goals of the Paris Agreement within the next few decades could have long-lasting impacts on global sea level rise in the coming centuries, new research finds.
The new study, published in Nature Communications (Mengel et al, 2018), estimates how delays in meeting the goals of the Paris Agreement could affect the total amount of sea level rise by 2300.
Under the Paris Agreement, countries have pledged to cut their rates of emissions in order to keep future global temperature rise “well below” 2C. To achieve this, nations agreed to reach “peak” CO2 emissions “as soon as possible”. This will be key to achieving “net-zero emissions” within the second half of this century.
The new research shows that the speed at which the world can cut its greenhouse gas emissions is becoming “the major leverage for future sea levels,” says study lead author Dr Matthias Mengel, a postdoctoral researcher from the Potsdam Institute for Climate Impacts (PIK) in Germany, in an interview with Carbon Brief.
The results suggest that sea levels could rise by 70 – 120cm by 2300 under a low emissions scenario (known as RCP2.6, see below). This level of sea rise could significantly increase the risk of flooding in coastal cities, such as New York, and island atoll nations. Currently, global emissions are tracking a higher scenario known as RCP8.5.
The results also indicate that, even once net-zero emissions are achieved and temperatures begin in fall, sea levels will continue to rise. This is because the drivers of sea level rise respond slowly to climate change. Global warming causes sea levels to rise in three main ways, Mengel says: thermal expansion (when seawater expands as the oceans absorb additional heat from the atmosphere); melting glaciers; and ice loss from the large ice sheets of Greenland and Antarctica.
The findings show that the world must “reduce its emissions as fast as possible” in order to protect future generations from extreme sea level rise.
- RCP2.6: The RCPs (Representative Concentration Pathways) are scenarios of future concentrations of greenhouse gases and other forcings. RCP2.6 (also sometimes referred to as “RCP3-PD”) is a “peak and decline” scenario where stringent mitigation and carbon dioxide removal technologies mean atmospheric CO2 concentration peaks and then falls during this century. By 2100, CO2 levels increase to around 420ppm – around 20ppm above current levels – equivalent to 475ppm once other forcings are included (in CO2e). By 2100, global temperatures are likely to rise by 1.3-1.9C above pre-industrial levels.
- RCP8.5: The RCPs (Representative Concentration Pathways) are scenarios of future concentrations of greenhouse gases and other forcings. RCP8.5 is a scenario of “comparatively high greenhouse gas emissions“ brought about by rapid population growth, high energy demand, fossil fuel dominance and an absence of climate change policies. This “business as usual” scenario is the highest of the four RCPs and sees atmospheric CO2 rise to around 935ppm by 2100, equivalent to 1,370ppm once other forcings are included (in CO2e). The likely range of global temperatures by 2100 for RCP8.5 is 4.0-6.1C above pre-industrial levels.
- Mengel, M. et al. (2018) Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action, http://nature.com/articles/doi:10.1038/s41467-018-02985-8
- Carbon Brief: https://www.carbonbrief.org/every-five-year-delay-in-meeting-paris-goals-could-add-20cm-to-global-sea-levels.