US, EU, China, India and Russia responsible for over half the projected sea-level rise caused by emissions under Paris Agreement pledges
The U.S. and four other countries are the biggest polluters and will be responsible for more than half of the estimated sea-level rise caused by emissions released in the 15 years following the Paris Agreement. According to a research team - led by Climate Analytics, Germany, and the Potsdam Institute for Climate Impact Research (PIK), Germany - 15 years of emissions released by countries under the current Paris Agreement, would alone cause sea-levels to rise by 20 centimeters by 2300.
This, say experts, is as much sea-level rise as scientists have observed over the entire 20th century. The pledges, made after first adopting the Paris Agreement in 2015, expire in 2030.
"Our results show that what we do today will have a huge effect in 2300. 20 centimeters is very significant; it is basically as much sea-level rise as we have observed over the entire 20th century. To cause that with only 15 years of emissions is quite staggering," said Alexander Nauels, lead author of the study from Climate Analytics.
The implications are clear, says the team, which states emissions today will inevitably cause seas to rise a long way into the future, and this process cannot be reversed. Nauels said, "The true consequences of our emissions on sea-level rise unfold over centuries, due to the slow pace at which the ocean, polar ice sheets and glaciers respond to global warming. The more carbon we release now, the more sea-level rise we are locking in for the future."
Just over half of the 20-centimeter contribution could be attributed to the top five polluters - China, U.S., EU, India and Russia - and emissions released by them will cause seas to rise by 12 centimeters by 2300. The findings have been published in the Proceedings of the National Academy of Sciences (PNAS).
"Five economies are responsible for more than half of the projected sea-level rise caused by emissions released in the 15 years following the Paris Agreement. To limit long-term sea-level rise, it is crucial that these countries step up their emission reduction efforts," said Johannes Gütschow from PIK, another author of the study.
When accounting for all the emissions released between 1991, the year after the Intergovernmental Panel on Climate Change (IPCC) published its first scientific assessment of climate change, and 2030, the long-term sea-level rise commitment of the five biggest emitters increases to 26 centimeters.
According to the researchers, the study is the first to quantify the sea-level rise contribution of human activity-induced greenhouse gas emissions that countries would release if they met their current Paris Agreement pledges, also referred to as nationally determined contributions or NDCs. The study, however, did not take into consideration the potential impact of an already irreversible melting of parts of the Antarctic ice sheet.
The team used sea-level modeling to estimate the contributions from historical greenhouse gas emissions and those currently pledged under the Paris Agreement to global mean sea-level rise until the year 2300. The model projects that greenhouse gas emissions up to 2030 would lock in approximately 1 meter of global mean sea-level rise by 2300 as compared with the baseline period 1986-2005, with about 20 centimeters of sea-level rise resulting from emissions pledged under the Paris Agreement.
"The 15 years from 2016 to 2030 commit about 8 centimeters of additional sea-level rise in 2100 or 20 centimeters of additional sea-level rise in 2300," said the study. This, said the team, "is one-fifth of the total committed sea-level rise caused by the emissions released from the start of industrialization up to 2030,"
"A focus on the 21st century fails to provide a complete picture of the consequences of anthropogenic greenhouse gas emissions on future sea-level rise and its long-term impacts. Here we identify the committed global mean sea-level rise until 2300 from historical emissions since 1750 and the currently pledged National Determined Contributions under the Paris Agreement until 2030. Our results indicate that greenhouse gas emissions over this 280-year period result in about 1 meter of committed global mean sea-level rise by 2300, with the NDC emissions from 2016 to 2030 corresponding to around one-fifth of that commitment," the findings stated.
The analysis, said the team, demonstrate that global and individual country emissions over the first decades of the 21st century alone will cause a substantial long-term sea-level rise. They recommend that governments need to scale up their efforts to reduce emissions.
According to Climate Analytics' Carl-Friedrich Schleussner, who also contributed to the study, governments need to put forward much stronger emission reduction pledges by 2020 to decarbonize at a pace in line with the Paris Agreement's 1.5°C temperature goal.
"Only stringent near-term emission reductions in line with achieving the 1.5°C long-term temperature goal of the Paris Agreement would provide a chance of limiting the long-term sea-level rise to below 1 meter," said the team.
They added, "Our ability to quantify and attribute such global sea-level commitments raises highly policy-relevant questions with respect to the need and responsibilities of supporting adaptation and loss and damage responses in low-lying coastal zones and small islands that will experience the most severe impacts."
Experts have projected in previous studies that as seas rise, extreme sea-level events will happen more often and increase flood risks. The September 2019 IPCC special report stated that sea level would continue to rise for centuries, and it could reach around 30-60 centimeters by 2100 even if greenhouse gas emissions are sharply reduced and global warming is limited to well below 2°C.
"While sea level has risen globally by around 15 centimeters during the 20th century, it is currently rising more than twice as fast – 3.6 millimeters per year – and accelerating. It could reach around 60-110 centimeters if greenhouse gas emissions continue to increase strongly," said the report on the ocean and cryosphere in a changing climate.
The IPCC report also warned that sea-level rise will increase the frequency of extreme sea-level events - which occur, for example, during high tides and intense storms - and this will have potentially devastating impacts for many coastal and island communities.