How many people live near the ocean?

The real question is, if sea levels rose due to melting glacial ice, what percentage of the word's population would get their feet wet? There are several problems with addressing this question, including the fact that it depends on how high sea levels rose. Most studies or calculations are based on what most people consider to be a large rise in sea level of about 10 meters/30 feet. Given this sort of consideration, the number of people living in the global food zone is significant. Here are a few tidbits from the Intertubes:

  • Three-quarters of the world's mega-cities are by the sea.*
  • By 2010, 80 per cent of people will live within 60 miles of the coast.*
  • 2010 some 80 percent of people will live within 62 miles of the coast, with about 40 percent living within 37 miles of a coastline.*
  • "For a while, it was said, 'Oh, two-thirds of all the population lives within 100 kilometers of a coastline," ... The numbers showed that low-elevation areas (under 10 meters/30 feet) are home to 634 million people...."Roughly one in 10 persons in the world lives in this low-elevation coastal zone," Balk says.*

Current estimates for the absolute maximum sea level rise, if the glaciers at both polls melted, range from 225 to 365 feet, with the latter being more likely accurate. If sea levels rose that much, coastal lands would be depressed several meters and transgressive erosion would also occur. So, for instance, even though Long Island has many points that are above 300 feet or so, none of it would survive the transgressive erosion because it is all glacial till. It is hard to extrapolate from the numbers above to a 100+ meter rise, and improper to do so, but consider that if the human population is concentrated near the seas, and 10% live below the 10 meter line, then it is probably true that well more than half live below the 100 meter line, and many more within the area that would be claimed by the sea through erosion and depression.

I've only done a cursory check for sources. If you have better information, please send it my way and I'll update the post.

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Well the Mississippi river valley might flood up to Cape Girardeau, Missouri (current elevation 351 ft above sea level). Florida would vanish (highest point 345ft above sea level). The California central valley would flood. The Ganges river valley would flood beyond Allahabad. Bangladesh would vanish except for the Chittagong Hills. The Brahmaputra would flood to above Dibrugarh. The Indus would also flood a fair bit inland. The Nile would flood nearly to Aswan. Beijing is currently at 143ft above sea level.

Might be easier to enumerate the major cities that would be safe from immediate effects. Denver, Chicago, Dallas, Atlanta in the US. New Delhi in India, Moscow and Kiev, but not Paris or London or Berlin.

Greg: there's graph lying around the netheregions of my iMac that supplies relatively monotonic relationship: for every 1 m of sea level rise, we can expect 100 million fleeing
inhabitants. Or something like that. I will try to dig it up.

James, that would be great. Or, as we were discussing last night (this blog post is in response to a cocktail party conversation) people would be slowly backing up sloshing ankle deep in the water saying "Hey, what's going on here" until the got sufficiently uphill.

One of the problems is that the rate at which a proper study would be proposed, funded, and carried out to answer this question may be slower than the demographic shifts. What if Rio stagnated in grown for five years while Mexico City went up in population by 20%, or if regions like Indonesia had a small shift in economics or policy so people moved up or down five meters in that hilly terrain. Etc.

The majority of international trade in products like grain and oil is by ship. How many ports could continue to operate with even a 5m rise in sea level? I suspect very few.

Regarding a 100+m rise in sea level, I see that Lake Ontario would become the Bay of Ontario, with large parts of Toronto under water.

By Richard Simons (not verified) on 19 Oct 2011 #permalink

"if the glaciers at both polls melted"

I knew it was getting hard to vote, but that's ridiculous.

By Randolph the p… (not verified) on 20 Oct 2011 #permalink

Richard, I actually studies this indirectly when looking at sea level rise and coastal ecology. Everything would have to be rebuilt, of course, but the interesting thing is that in some regions harbors could simply ride "up hill" (the cities they would run into would have to be removed of course) and in other areas the good harbors would simply vanish and others would reappear in totally different places. Like, maybe, in your neighboring country, state, or province.

Yeah, regarding Toronto, this would affect the row boat races they have there, I imagine, but whale watching would become a possibility!

I don't see any sensible way to talk about this outside of a time frame. A 300 foot rise in sea level is huge. But if that's centuries from now, it has to be set in the context of what we think people will be doing then. And whatever we think there likely is wrong.

The shorter-term question may be more interesting. What is the maximum rise we might see in the next half-century? Five feet? Even that is enough to cause large problems in a lot of coastal communities. And I'm pretty sure people will still be wanting to live in Miami and NYC in fifty years.

Isn't 100m kinda crazy? I thought most estimates were looking at around 1 meter of sea level rise. We're not really expecting the polar ice to all melt. That'd be an apocalyptic scenario. Here's Earth in the Cretaceous, when the continents were sorta in a modern configuration and there was no polar ice:

Even that is unrealistic because there's been a lot of uplift. Here's the Earth in the Miocene, when there is Antarctic Ice, but even that isn't what anyone's actually expecting:

The folks at Columbia Univ/CIESIN have done tremendous work in geolocating the projected world population and making it accessible -- projected data are here: Historical data linked to low-lying areas are here, which answers most of the question as posed: The more precise LandScan data are licensed and require approval for use ( )

I think the number is around 200-600 million people. Sea level rise will also have some non-linear discontinuities due to erosion, land depression, and hurricane/cyclone flooding effects, so this depends on the modeling of those effects and the accuracy of the population grid.

Isn't 100m kinda crazy? I thought most estimates were looking at around 1 meter of sea level rise. We're not really expecting the polar ice to all melt. That'd be an apocalyptic scenario.

Crazy, yes. Unlikely, no. Yes, one of the points I've been making lately is that the estimates are not realistic. They only refer to a small part of the likely melting. One meter is ridiculous. At the low end of the scale and over coming decades, expect at least that. At the higher end of the scale, at the level of ice caps melting, 100 meters is the minimum estimate, probably more like 110 or so. It is crazy but it is not wrong. It is simply what would happen.

Carbon was at 200 ppm. Now it is almost 400. The maximum during the times you are referring ot was between 3000 and 4000.

Does this mean that Carbon levels have to get to 4000 to melt all the ice caps? No. The process is far more complex than that. The northern ice including the Greenland Glaciers can melt with much much lower numbers ... we may be close enough now ... because the northern polar region is integrated with the rest of the climate system with no buffering, and it is only semi-polar, there being an ocean in the north. The southern ice cap is isolated by sea and thus also by air currents, so it may take much more to melt that. Probalby less than 3,000 however.

So, other than slowdowns because of economic crisis, what is the event, force, or change that is going to stop us from putting about 200 ppm per 40 years or so into the atmosphere, or even more? Tell me what that is, then I'll tell you that maybe the ice caps wont' melt.

Regarding the reconstructions of earlier sea levels: Those are not relevant. As you point out, there is uplift and other changes. But we don't need those reconstructions. We have maps of the present. We just need to know how many cubic km's of water is trapped in ice.

Short term, sea level rise is probably very small. Medium term (a few decades) it is going to be a real problem, and it is too late to fix that. We can't reverse the current trends fast enough for there to not be problems, and we are already seeing problems. All those are the responsibility of the Global Warming Denialists.

The longer term, say with multi-tens of meters of sea level rise is not stoppable by any means I know of, because there is no political process that will do that. Mass die-offs of humans due to epidemics or whatever could always happen, but otherwise, I see not real hope. But, we can pretend that a long term plan will reverse the process of, essentially, releasing that Cretaceous Carbon back into the atmosphere. But we are lying to ourselves. We have no mechanism for doing that. The best we can do is the Tea Party.

Estuaries and large cities not held to ransom by the Tea Party can address the problem by investing in infrastructure. This one is both beautiful and a fine example of forward planning. Even so, it is only expected to be enough until the middle of the current century and planning for the next stage - a higher barrier downstream of this - is already underway.

That's a single channel - mapped, monitored and corseted* for two thousand years. Now imagine trying to do it with NYC, let alone the Brahmaputra.

* I was lucky enough to be working nearby when a Museum of London team excavated a Roman revetment by London Bridge Station, so I am not making this up!

By maureen.brian#b5c92 (not verified) on 20 Oct 2011 #permalink

Greg and Schenck, I think the forecasts of 1/2 meter to a meter refer only to thermal expansion, not ice melting. Everything I've read says if all the ice melts, it's 100 meters.

A lot of people got their feet (and basements) wet in the Baltimore area a few years ago during hurricane Isabel. One needs to consider the storm surges and not just calm conditions.
I think it was the Department of Defense that reported on what vital infrastructure along the Gulf Coast would need to be replaced due to global warming.

We have heard many climates predictions of various conditions with dates of 2050 and 2100; e.g. the oceans will rise 30-40 cm by 2050, or 2 meters by 2100. While these may be correct, folks not in the science community may have the impression that if we can get to 2100 and it's not to bad, we're home free. As Greg clearly understands (but readers of USA Today may miss) it will continue to get worse for centuries after that, before it gets better (if ever).

The answer of how many people live near the ocean was never specifically addressed and I donât think it can be given the non-specificity of the question. More addressed was the question of how many people would be affected if the sea levels rose. If the two glaciers melted on each poll we are looking at a major global problem. There would not be a single person unaffected by the flooding waters. Now if you are asking how many people would actually get wet, that would be difficult to answer. A clear response wasnât given because you would have to take a census of how many people live within the areas that would be affected, but you would have to know exactly the boundaries affected. Al in all this is a really tough topic to think about.

Good info but I think 100 meters a lot? I think it would be less.

Thank you so much for your fascinating post, but I thought it worth mentioning that no one is claiming sea level rise of even close to 10 meters in the short term. I've seen estimates between 0.25 meters and a meter over the next hundred years. While certainly unfortunate, that is not exactly a New York killer. Interestingly New York has actually been growing faster than that due to land recrimination.

Isaac, thanks for your comment.

People (as in climate scientists) are indeed suggesting that the Greenland and West Arctic ice sheets are at risk of significant melting, and that would produce a great deal of sea level rise. There is real meaning to the term "short" vs. "long" term here. If we build cities as we do now for the next century or two, and the sea level rises several feet by 200 years from now, the cities flood. If something unexpected happens and the sea level rises in half that time, the cities still flood.

Meanwhile, a very small amount of sea level rise is implicated in the flooding of the subways in New York City during Hurricane Sandy.

The problem is, we don't have at present a good way to estimate the timing and nature of melting in the future. But we do know this: Avoiding extensive glacial melting requires curtailing the transfer of fossil carbon into the atmosphere. We've not done anything real to curtail that process. The timing and magnitude of future sea level rise is unknown. That we are at present doing virtually nothing to stop this is a fact.

Meanwhile, current sea levels seem to be enigmatically low, based on the palaeorecord. Think of sea level as a range that can occur in a given climatic setting. It is very likely that at present we are NOT at the high end of that range, and we may well be at the low end of that range. This is of concern.

Wow! When did IQ's suddenly take a nosedive. Here we are in 2014, and people are still counting on computer models (like the ones that can't predict the weather?) to tell us what's going to happen a few decades out? Global warming is a natural process that Earth continues to cycle through. Instead of forecasting doom, gloom and blame, you should be preparing yourselves. Adjust or die - those are your two options. All your worrying, forecasting, and even action will not stop it. REPENT.

By Noneya Bizness (not verified) on 31 Jan 2014 #permalink

None ya, at this point in history it is safe to assume that you know you are wrong. So you are lying. Why? Are you getting paid or are you just some kind of jerk?

NASA says over 1/3 (NOT 80%!!) of human pop. lives w/in 100 km.s (60 miles) of sea in 2010. get your facts right! your blog pops up high on google and kids will be totally misled -- this is a huge discrepancy -- CHANGE your blog please to reflect correct numbers -- Thnakyou

By Tom Killion (not verified) on 11 Apr 2014 #permalink

Tom, do you have a link to your NASA number? That would be interesting.

Also, do read the blog post before you criticize it so obnoxiously. Most kids will probably not have a problem reading this. But do supply the link please.

Dry in terms of fresh water has nothing to do with coastal.

By Brian Donovan (not verified) on 02 Jul 2014 #permalink