Why do sea levels not rise uniformly around the world?


While reading the article Hawaii’s Beaches Are in Retreat, and Its Way of Life May Follow on The New York Times’s website, I was surprised to find out that sea levels do not rise around the world at a uniform rate. Assuming that the global warming is true (I think there’s enough credible evidence for it – but I don’t want a debate on the veracity of global warming – therefore, just assume it’s true), what may be the reason for the non-uniformity?

asked May 15 ’12 at 15:35

1 Answer

up vote 5 down vote accepted

There’s a good article about this at http://climate.nasa.gov/blogs/index.cfm?FuseAction=ShowBlog&NewsID=239. Since it’s a NASA blog I assume it’s reasonably trustworthy. The key points are:

  • ocean currents and the prevailing wind patterns cause water build ups in some areas
  • ocean temperatures vary and higher temperature areas have higher levels because the water density is lower
  • the weight of ice sheets affect the Earth’s axis of rotation and the water distribution

I must admit I’m not sure about the last of these as it seems to me it would be a very small effect. Finally, another longer term effect I’ve seen mentioned in some discussions is that land rises as it’s freed from the weight of the ice. The north of the UK is still rising, and the south still sinking, after the ice melted at the end of the last ice age.

answered May 15 ’12 at 15:59
John Rennie
Wrt your third point, I think the issue is also that some pieces of land rise due to less ice sheets elsewhere. So the apparent sea level rise at those locations is less. – Bernhard May 15 ’12 at 17:00
@Bernhard sort of. What happened during the last glacial was that the crust under the ice sheets was pushed down by IIRC several hundred meters while crust south of the icesheets rose by a similar amount. With the ice sheets gone the crust is flexing back to its pre-glacial shape. in the extreme case, part of northern Canada is rising almost 2cm/year. In coastal areas mean sea level rises or falls with the movement of the crust. en.wikipedia.org/wiki/Post-glacial_rebound – Dan Neely May 16 ’12 at 17:46
There’s very small (0.7ms/century) shift in the length of the day due to mass distribution changes. I doubt this is enough to affect the distribution of the ocean meaningfully. – Dan Neely May 16 ’12 at 17:47

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