Sea-level rise past and future

Press release by the Potsdam Institute for Climate Impact Research (PIK)

02/23/2016 (embargo expired)

Sea-level rise past and future: robust estimates for coastal planners

fp_sea_level_globeSea-levels worldwide will likely rise by 50 to 130 centimeters by the end of this century if greenhouse gas emissions are not reduced rapidly. This is shown in a new study led by the Potsdam Institute for Climate Impact Research that, for the first time, combines the two most important estimation methods for future sea-level rise and yields a more robust risk range. A second study, like the first one to be published in the US Proceedings of the National Academy of Sciences, provides the first global analysis of sea-level data for the past 3000 years. It confirms that during the past millennia sea-level has never risen nearly as fast as during the last century. Together, the two studies give critical information for coastal planning. For expert assessments of future sea-level rise, the authors make the tool available online.

“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,” says Anders Levermann, Research Domain Co-Chair for Adaptation at the Potsdam-Institute for Climate Impact Research (PIK), scientist at Columbia University’s Lamont-Doherty Earth Observatory,  and co-author of the study on future sea-level rise. “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 Paris Agreement is implemented, adaptation is a challenge

The scientists will make the computer simulation code available online so experts can use the information and the estimation tool for risk assessments. Even if ambitious climate policy follows the 2015 Paris Agreement, sea levels are projected to increase by 20 to 60 centimeters by 2100 – hence the relevance for coastal protection. “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 a few weeks ago.”

For future sea-level rise, the scientists combine two approaches. To forecast sea-level rise, some scientists use  process-based computer simulations that calculate the contribution of melting glaciers, ice sheet mass loss and the thermal expansion of sea-water from physical laws – warmer water takes more space. These simulations are computationally costly and slow. As an alternative, statistical analyses have been used to assess future sea-level rise quickly at low computational cost. “We designed our tool in a way it is consistent both with the past observations of sea-level rise and the long-term physical processes in the different elements of the Earth system,” says lead-author Matthias Mengel from PIK. “Importantly, our calculation method is fast, which makes it easy to reproduce and allows for a lot of simulation runs to provide probabilities of sea-level rise.”

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,” says 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.”

During past millennia sea-level has never risen as fast as during the last century

The study on future sea-level rise turns out to be confirmed by the other one on past sea-level rise: they yield nearly identical sea-level rise estimates for the 21st century. Also, the new estimates overlap with those of the latest IPCC report.

“Our study is for sea level what the now well-confirmed famous ‘hockey stick’ diagram was for global temperature,” says 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.” Based on the analysis of the past millennia of natural sea-level variations, the new study was also able to estimate how much human activities have contributed to modern sea-level rise: Almost certainly more than half of the 20th Century rise has been caused by human activity, possibly even all of it.

Confirming previous assumptions, as boring as it might sound, is of key relevance for the progress of science. “We can now show the effect in an unprecedentedly robust way, based upon the statistical analysis of a global database of regional sea-level reconstructions,” says Rahmstorf. “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.”

Article on future sea-level rise: Mengel, M., Levermann, A., Frieler, K., Robinson, A., Marzeion, B., Winkelmann, R. (2016): Future sea-level rise constrained by observations and long-term commitment. Proceedings of the National Academy of Sciences (PNAS) [DOI:10.1073/pnas.1500515113]

Weblink to the article on future sea-level rise:

Weblink to source code for future sea-level rise approximation tool:

Article on past sea-level rise: Kopp, R.E., Kemp, A.C., Bittermann, K., Horton, B.P., Donnelly, J.P., Gehrels, W.R., Hay, C.C., Mitrovica, J.X., Morrow, E.D., Rahmstorf, S. (2016): Temperature-driven global sea-level variability in the Common Era. Proceedings of the National Academy of Sciences (PNAS) [DOI:10.1073/pnas.1517056113]

Weblink to the article on past sea-level rise:

For further information please contact:
PIK press office
Phone: +49 331 288 25 07
Twitter: @PIK_Climate 

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1 Response

  1. Poo Carson says:

    This morning up here in the Great White North I walked my 4 plus miles through piles of snow. Had I a dog, I would have mushed. We’re only 88th in Canada for snowfall in these parts so I suppose it could have been better. I like snow. I’m a Canuck, eh?

    Pity those modellers at Potsdam didn’t spend more time in their math or logic classes. I especially like the photo of “Waves rolling towards the shore” from thinkstock as shown on their site. I mean isn’t that what waves do? How alarming! How extreme!

    Environmentalists generally fall into three groups: those who love the modern world, those who despise the modern world and the ultra-wackos who loathe everything from capitalism to working, most especially the latter.

    Modern environmentalists support industry, want to grow the economy, embrace scientific and technical progress and are for sound conservation planning and against pollution. The anti-modern environmentalists blame the modern world for environmental problems and would prefer to live in tents, electricity, heat and water supplied, free of charge, of course. The wackos are prepared to go to war for the environment, as they misunderstand it, providing any fighting is done by others and the government finances their part, such as it is.

    The moderns are doers not talkers and picketers. They don’t demonstrate, file petitions, agitate, or demand special status from governments. Rather, they raise private, not public, money to improve fish habitat, restore wetlands, plant trees, stock lakes, and repair degraded lands. Ducks Unlimited and the Ontario Federation of Anglers and Hunters come readily to mind here in the Great White North.

    The Antis never describe their end game. It is all magic allowing us to retain our jobs, cars, air travel, food, quality medical care and the many benefits of an industrial society like increased lifespans and better health not to mention our vastly improved finances since we have moved indoors from our tents and caves.

    The Antis are process driven. Give, and I do mean give, them a grant, a desk and a computer and life is good. The “Evolution” will begin via media demonstrations, sit-ins, petitions and pictures of pussy cats, I mean baby seals. Their agenda, such as it may be, is based on other people’s work.

    The Environmentalist Game is over. Somebody turn out the lights. Even the U. S. Supreme Court can see it calling, as they did earlier this month, for an immediate halt to the Narcissist in Chief’s Executive Ordered ‘Clean Power Plan’. “This could be the proverbial string which causes Paris to unravel,” The New York Times said.

    As usual, the Narcissist in Chief was beating his chest with an empty boast based on an unconstitutional plan or so said the 29 states and state agencies that successfully argued the “plan” needed congressional approval to proceed. I mean, isn’t that what a Congress is for after all.

    Obama thinks all his phony deals will give him a legacy beyond record debt (see Congressional Budget Office, White House Budget Office, World Bank, IMF, among others) rising health care costs and a litany of broken promises.

    More than 2,400 coal-fired power stations are under construction or being planned around the world. Obama Green Deal China is building 368 plants and planning a further 803. Potsdam has confirmed this. India is building 297 and planning 149 more. Japan has 40 plants in the pipeline and five under construction. Some legacy.

    Quite a deal that Paris deal, legacy wise. Not as good as the Iran deal which puts weapons and money into the hands of the largest sponsor of terror in the Middle East or the Syrian peace plan which allows for shooting and bombing!
    The 5 Star Paris gab fest allowed each nation to set their own goals and measure their own progress. Oh yes, and if by some idiotic miscalculation these phony targets are missed, well, there is no penalty. Our Liberals call targets like that “aspirational.” They never achieve them either.

    The Narcissist in Chief’s “transformative presidency” will not be remembered as the time when “the rise of the oceans began to slow and our planet began to heal” but rather as a time of lovely, but meaningless words, and lots of them.

    Last year and into early 2016 El Niño, the Pacific Ocean phenomenon that brings unusually warm weather to us occasionally, created propaganda opportunities for the eco-warriors. Good thinking, but if they can’t win converts on the warm days what will they ever do when the anticipated La Nina brings unusually cold weather?

    The American election season does not bode well for the eco-warriors either. The Democrats can offer only an unpopular Hillary or an unelectable Bernie. Though the demographics are massively against them for the Presidency, Republicans will still hold the purse strings through their control over the legislature and most States. Democratic Executive orders will be the order of the day.

    Hope does not spring eternal for the eco-warriors. The Narcissist in Chief has taught them that Hope is a 4 letter word. Oh yes, and don’t live too near water, in flood plains or at sea level. Historically, it has never been smart no matter the weather.

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