Last week, a group of scientists led by Anders Levermann of the Potsdam Institute for Climate Change Research released a paper that made a stark forecast: For every 1 degree Celsius of temperature increase, the world will eventually experience a 2.3-meter increase in sea level. That means that should carbon emissions continue to rise at or near current rates, and temperatures soar 4 to 5 degrees C in the next century or two, the world could well experience sea level increases of many meters — dozens of feet — in the centuries and millennia to come.
Yale Environment 360: What are the main points that you think readers should take away from this paper?
Anders Levermann: The real new thing is we have asked the question not how much sea level rise will there be in 2100, but rather how much sea level rise are we already committed to at a certain level of global warming? And these numbers are much higher than the numbers we expect in 2100.
Sea level is like a big ball — it takes a while until you get it rolling, but once it’s rolling you can’t stop it easily. The projections by 2100 are significantly below 2 meters [6.6 feet] of global sea level rise. But we expect over a period of 2,000 years a sea level rise of 2 meters for each degree Celsius of warming. Now if you look at the projections for temperature by 2100, a business-as-usual scenario in which we increase the CO2 emissions every year like we have done in the past would lead to a warming of about 4 to 5 degrees Celsius [7 to 9 degrees F]. And long-term, 4 to 5 degrees in our study translates to something in the vicinity of 9 meters [29.6 feet] of sea level rise. So it’s less than 2 meters sea level rise projected for 2100, but in the long term it’s 9 meters.
e360: So you’re saying once this warming is in the atmosphere, it’s going to take a while for the melting of various ice sheets and the thermal expansion of water to catch up to it?
Levermann: What I’m saying is once you put a certain amount of CO2 in the atmosphere, you’ll have to live with the corresponding warming for a long time. This is a problem we look into with respect to sea level rise because this long-term warming results in a long-term sea level rise that will not stop in 2100, but will go on and on for a long time.
e360: Could you discuss your confidence in your findings and what measurements and models you used to make sure that the numbers you came up with represent a pretty reasonable forecast.
Levermann: What we have done is we take the state of the art physical models for each component that is relevant for sea level rise — the thermal expansion of the ocean, melting of [mountain] glaciers, and melting of the
What I would say is we simply put expiration dates on certain cultures and societies.’Greenland and Antarctic ice sheets — we take these four models and ask the question: How much sea level rise do you get after 2,000 years when you elevate the temperature? Then we add them all together and we get a result for the total sea level contribution for different levels of warming and then we compare this to the paleological data. All of this gives a consistent picture, which says we can expect an increase in sea level of 2.3 meters for each degree of warming.
e360: Tell me a little bit about the paleo data?
Levermann: When you go into paleo records you can never use direct measurements because there was obviously no one around taking measurements 10,000 years ago or even longer. So that’s why you use what we call proxy data, where we use certain chemical components or isotopes in order to make statements about, first, the temperature, and then the sea level. Sea level has an additional way we can derive it from, and that’s simply from looking at the sea level that you see in the geological record. In some places around the world, you can simply see where the sea level was at certain times in history.
e360: Let’s say we continue on the current path of emissions and that by 2100 we are 4-5 degrees Centigrade hotter than we are now. How long after that do you think you could begin to see significant sea level rise as the Antarctic and Greenland ice sheets begin to melt at a more rapid rate?
Levermann: Significant is very much defined here by society. The 20 centimeters [8 inches] that we have observed in the last 100 years are significant for the smaller island states in the Pacific, which are inevitably going to vanish in the future. And also, for example, tropical storm Nargis in Myanmar in 2008 went much farther inland because of this additional 20 centimeters than it would have in pre-industrial times.
So the question of what is significant is very much dependent on the coastline you look at and what society wants or can adapt to. I would say that a meter in the 21st century would be highly significant for the Netherlands
People will have to reconsider what’s home and how long you build a home for.’and Europe, but also for London and Florida and New York and so on because you always have to add on top the storm surges.
We picked the 2,000 years date because it is far enough in the future so that the small scale variations and the sea level rise have been averaged out. So we can be quite certain that after 2,000 years this kind of sea level rise will be observed, but it could be well before that.
e360: If the conclusions of your research are correct, civilization is going to be looking at sea level rise that could well exceed 5 meters [16 feet], or could be 10 meters within the next 2,000 years. These are really massive increases. What do you think your paper says about adaptation and what the world needs to be doing now about adaptation?
Levermann: What I would say in short is that we simply put expiration dates on certain cultures, on certain societies around the globe. Definitely for some small island states in the Pacific and in the tropics in general, but also for regions that are now low-lying, like the Netherlands and Bangladesh, and also regions in the U.S. And that simply poses the question of what kind of infrastructure we build, what buildings we build — the churches, the power plants, and so on. For what time period do we build them and is there a cultural heritage we have to abandon in the long run?
e360: Your term “expiration date” is striking. With 5 or 10 meters of sea level rise, you would be looking at an expiration date, if you would, for much of the world’s coastal areas, would you not?
Levermann: I think it’s culturally very important whether we have an open-ended future or whether we can say there’s a limit to it. If you are living on a Pacific island, and you simply know that in 100 years your home won’t be there anymore, then I would assume you build your society differently, you think differently about your children, about your grandchildren. And with these kinds of numbers we’ll have to do something similar. People will have to reconsider what’s home and how long you build a home for.
e360: How would you characterize society’s understanding and acceptance of these facts at this point?
Levermann: There’s one very important aspect to the adaptation problem and that is that people consider this to be a local problem and I would strongly argue against it. We are living a globalized world and our societies are relatively fragile already. Now after Fukushima — the Japanese catastrophe — we had supply failures in Europe in the automobile industry.
I haven’t decided myself what is the price we are willing to pay for saving the coastline of Florida.’The same was true after the great recent Thailand flood — we had a shortage of hard drives in the U.S. and in Europe for months in 2012 and this was really not expected. So we had a remote event which impacted us from afar. Now if we don’t get hard drives for a while that won’t collapse a society obviously. But what happens if we get a whole series of these kinds of impacts like Katrina and Sandy in the same year, and a drought and a heat wave that brings the California electricity sector into collapse or something. Will this stay within the U.S. or will it spread around the world? And this is why we need to consider adaptation as a global problem.
A lot of transportation routes at the moment depend on harbors or infrastructure that is close to the coastline. If, for example, a storm surge would destroy the harbor of Rotterdam, where a lot of containers go through, you would strongly disrupt the supply chains for a lot of production in different countries. This is why sea level rise and the associated storm surges directly lead into a global adaptation problem because what we have to do is we have to rearrange our supply network in a way that is robust against terror attacks of nature, if you like. That’s in a sense what it is — it’s not intentional, obviously that’s why it is not a terror attack, but it’s a localized disruption by nature on our supply chain, which requires a robust supply network. I believe that this global supply network would adapt by itself, if it was given the information about its vulnerability. We are planning to set-up a Web-platform similar to Wikipedia where such information is gathered and provided. It will be launched at www.zeean.net.
e360: When we are talking about 500 years, 1,000 years, 2,000 years, that’s really distant in time. In 100 years one can imagine one’s grandchildren for example, but in 2,000 years of course that’s unimaginable. How do you get society to care about potential long-term impacts when they and their grandchildren will be long gone?
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I personally believe that we cannot adapt to a warming of 4 or 5 degrees [C] because the increase in extreme events and also sea level rise, combined with extreme storm surges, will simply increase the pressure on our complex societies, which might bring them to the verge of collapse. Obviously, we do not know whether this will happen, but I think that such a threshold is out there somewhere — we just do not know where. We do need to adapt to the climate change that cannot be avoided anymore, but we definitely need to mitigate any warming that we cannot adapt to.