‘Our study is for sea level what the now well-confirmed famous ‘hockey stick’ diagram was for global temperature’
The global rise of sea level may not be as dramatic or as easily visible as some other signs of global warming like melting glaciers, but it will be one of the most destructive and expensive long-term impacts. With a huge percentage of the world’s population living in coastal regions, society will need to take costly measures to protect people. In some cases, there will no option but to move entire communities away from the rising waters.
While there is still some uncertainty among climate scientists as to the extent of future sea level rise, there is little doubt that the current increase is unprecedented in recent times, according to a recent study by scientists with the Potsdam Institute for Climate Impact Research.
“Our study is for sea level what the now well-confirmed famous ‘hockey stick’ diagram was for global temperature,” said Stefan Rahmstorf, co-author of the paper on past sea-level rise and Co-Chair of PIK’s research domain Earth System Analysis. “We can confirm what earlier, more local sea-level data already suggested: during the past millennia sea-level has never risen nearly as fast as during the last century.”
The researchers said greenhouse gas emissions have caused at least half of the observed sea level rise in the 20th century, and possibly even all of it.
While the study didn’t break new ground in terms of projections, it’s important to be able to show with great certainty how much sea level will rise, Rahmstorf said.
“The new sea-level data confirm once again just how unusual the age of modern global warming due to our greenhouse gas emissions is – and they demonstrate that one of the most dangerous impacts of global warming, rising seas, is well underway.”
Barring any catastrophic climate feedback loops that could accelerate the meltdown of Arctic and Antarctic ice, the researchers said sea-levels worldwide will rise by 50 to 130 centimeters by the end of this century if greenhouse gas emissions are not reduced rapidly.
“With all the greenhouse-gases we already emitted, we cannot stop the seas from rising altogether, but we can substantially limit the rate of the rise by ending the use of fossil fuels,” said PIK’s Anders Levermann, who specializes in climate adaptation.
“We try to give coastal planners what they need for adaptation planning, be it building dikes, designing insurance schemes for floodings, or mapping long-term settlement retreat.”
Even if the world’s countries live up to the 2015 Paris climate agreement, sea level will rise 20 to 60 centimeters by 2100.
“This is quite a challenge, but less expensive than adaptation to unabated sea-level rise which in some regions is impossible”, Levermann adds. “If the world wants to avoid the greatest losses and damages, it now has to rapidly follow the path laid out by the UN climate summit in Paris.”
The likely future sea-level rise cannot be brought down to just one number, but is represented as a range, which at first sight might seem large.
“The range allows for a risk assessment,” said Ben Marzeion from the University of Bremen, Germany. “Coastal Planners need to know how a reasonable worst-case scenario as well as a well-founded best-case scenario look like to weigh chances and costs. The best available science is now converging towards a common uncertainty range of future sea-level rise. Curbing greenhouse gas emissions now gives us the chance to prevent sea level rise to accelerate further.”