Humanity’s difficulties dealing with climate change trace back to a simple fact: We are animals. Our cognitive and limbic systems were shaped by evolution to heed threats and rewards close by, involving faces and teeth. That’s how we survived. Those systems were not shaped to heed, much less emotionally respond to, faceless threats distant in time and space — like, say, climate change. No evil genius could design a problem less likely to grab our attention.

This is a familiar point, but some new research on sea level throws it into sharp relief. Let’s quickly review the research, and while we do, keep this question in the back of our minds: “Does this make me feel anything? Even if I understand, do I care?”


This post is not about seal levels, so I'm outta here.

butterflydreamThis post is not about seal levels, so I’m outta here.

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The first bit of research is a paper that’s gotten a lot of press attention: “The multimillennial sea-level commitment of global warming.”

Sea-level rise is a vexed issue in climate discussions because everyone wants to know where sea level’s going to be in 2050, or 2100 — years that we can, at least dimly, imagine. I’ll still be alive in 2050, presumably, and my kids or grandkids in 2100, with any luck.

The problem is that it’s much easier to project long-term sea levels than short term. It’s difficult to nail down the near-term timing of “nonlinear” (abrupt) events involving, say, ice sheets, but over a few thousand years, it all evens out. A century just isn’t that long in climatic terms.

A team of researchers led by Anders Levermann at the Potsdam Institute for Climate Impact Research has done something novel. They said, screw the short term. We know that CO2, once it’s in the atmosphere, is effectively permanent. We know that for a given level of CO2 concentrations, eventually you get a given temperature, and for a given temperature, sooner or later sea level will rise to adjust. When you raise the temperature, you “lock in” a certain amount of sea-level rise, even if you don’t know exactly how quickly it will happen.

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So Levermann and co. set out to determine how much sea-level rise gets locked in for every degree that global average temperature rises. They modeled all the main drivers — thermal expansion (warm water expands), glaciers melting, the Greenland ice sheet, and the Antarctic ice sheet — and then compared the results to the paleo data to make sure they matched up with the patterns in the historical record (they did).

This is, scientifically speaking, easier to do that predicting short-term sea levels. “On a 2,000-year time scale,” they say, “the sea-level contribution will be largely independent of the exact warming path during the first century.” A lot of stuff that might be abrupt or unpredictable over the next century or two washes out over the long-term.

So what’s the verdict? Long story short, for every degree Celsius that global average temperature rises, we can expect 2.3 meters of sea-level rise sometime over the ensuing 2,000 years. (U.S. translation: for every degree Fahrenheit, 4.2 feet of rising seas get locked in.) We are currently on track to hit 4 degrees Celsius by 2100, if not sooner. That means locking in 9.2 meters, or 30 feet, of sea level rise. Suffice to say, that would wipe out most of the major coastal cities and towns in the world.

PNAS: sea level lock-in

PNASClick to embiggen

There you have it: If we stay on our current trajectory, by the end of the century we will ensure the eventual destruction of our coastal developments. But! That destruction will happen at some point over the next 2,000 years. Maybe not for 100, maybe not even for several hundred, long after you and your children and your grandchildren are dead.


Do you care? Should you? Should you mobilize and put lots of money and effort toward an emissions-reduction regime that will prevent it? If you knew you were committing the place you live to destruction in 100 years, would it move you to action? What about 200 years? 500? 500 years ago was 1513, the year Juan Ponce de León “discovered” Florida and claimed it for Spain. I wonder if he worried what would happen in 2013.


Sea-level “lock in” is happening 10 times faster than sea-level rise itself, but thanks to the long time lag, it’s even more invisible. To bring it a little closer to home, Ben Strauss at Climate Central follows up on Levermann’s analysis by examining what sea-level rise might mean for America. (It’s a preview of a new paper that will be published Monday in the Proceedings of the National Academy of Sciences.) [Editor’s note: Strauss is on Grist’s board of directors.]

There’s grim news right up front:

To begin with, it appears that the amount of carbon pollution to date has already locked in more than 4 feet of sea level rise past today’s levels. That is enough, at high tide, to submerge more than half of today’s population in 316 coastal cities and towns (home to 3.6 million) in the lower 48 states.

That’s a done deal. Those places are effectively doomed. But the choices we make today will have huge repercussions on sea levels to come:

By the end of this century, if global climate emissions continue to increase, that may lock in 23 feet of sea level rise, and threaten 1,429 municipalities that would be mostly submerged at high tide. Those cities have a total population of 18 million. But under a very low emissions scenario, our sea level rise commitment might be limited to about 7.5 feet, which would threaten 555 coastal municipalities: some 900 fewer communities than in the higher-emissions scenario.

If we take heroic measures, we could lose “only” 555 American towns and cities to the ocean. Whee!

If we do nothing and stay on our current trajectory, over 1,400 are threatened, including:

Nationally, the largest threatened cities at this level [50 percent submerged at high tide] are Miami, Virginia Beach, Va., Sacramento, Calif., and Jacksonville, Fla.

If we choose 25 percent [submerged] instead of 50 percent as the threat threshold, the lists all increase, and would include major cities like Boston, Long Beach, Calif., and New York City.

To find how f’d your coastal town is, here’s a nifty interactive gizmo.

So, yeah, lots of American places are screwed over the long term. But how long? I mean, if it’s in 2,000 years … who knows if humanity will even exist? By then, surely the robots will have taken over.

Strauss addresses this question:

The big question hanging over this analysis is how quickly sea levels will rise to the committed levels. Neither Levermann and colleagues’ analysis, nor my new paper, address this question.

In a loose analogy, it is much easier to know that a pile of ice in a warm room will melt, than to know exactly how fast it will melt.

Levermann and company do put an upper limit of 2,000 years on how long it will take the sea level commitments described here to play out. Recent research indicates that warming from carbon emitted today is essentially irreversible on the relevant timescales (in the absence of its massive-scale engineered removal from the atmosphere), and will endure for hundreds or thousands of years, driving this long run unstoppable sea level rise.

On the other hand, our sea level rise commitment may be realized well before two millennia from now. The average rate of global sea level rise during the 20th century was about half a foot per century. The current rate is 1 foot, or twice that. And middle-of-the-road projections point to rates in the vicinity of 5 feet per century by 2100.

Such rates, if sustained, would realize the highest levels of sea level rise contemplated here in hundreds, not thousands of years — fast enough to apply continual pressure, as well as threaten the heritage, and very existence, of coastal communities everywhere. [my emphasis]

OK, so we’re probably talking hundreds instead of thousands of years. Let’s say, just for the sake of argument, that business as usual will put Miami under water in 100 years.

What is Miami worth to us? What will it be worth to the humans of 2113?

It depends, I would say, on what you think of those 2113 humans. Most people assume that humanity is going to experience a continual rise in wealth, technological sophistication, and living standards. That’s certainly the assumption baked into most economic models. If it’s true, the people of 2113 are going to be immeasurably more wealthy than us. Perhaps they’ll live in floating cities, or space stations. Perhaps they will drive amphibious vehicles. Perhaps they will leave their corporal bodies behind entirely and live on as clusters of electrons in Google data centers. What need will they have of Miami? They have transcended Miami. At any rate, we’re not inclined to worry about them. They’ll be better prepared to deal with the loss of Miami than we are to prevent that loss. Or so the thinking goes.

But there’s another way of seeing it. What if, as many people fear, we are churning through irreplaceable natural capital and our descendents are going to have less to work with than we do? What if our descendents face a world of resource shortages, insane weather, and denuded biodiversity? What if they need all the help they can get? If that’s true, it seems unthinkably irresponsible to allow a huge swath of our invested energy and capital to wash away in the sea.

What do you think? Do you care — really feel it, in your gut — that we’re in the process of consigning hundreds of American towns and cities to destruction? What does being a good ancestor mean to you?

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