[extropy-chat] Re-save the world
pharos at gmail.com
Thu Feb 15 12:06:35 UTC 2007
On 2/15/07, Robert Bradbury wrote:
> Interesting. A great application of the mapping software that would have
> been completely unavailable a decade ago.
> You have to zoom in quite a bit to see what would go under with a 7m rise in
> sea level.
> Where I live is fine (I think I'm at ~200 feet). One does however lose some
> interesting airports. JFK and Regan (National) almost entirely and
> significant amounts of Logan and Laguardia. I suspect it would be major
> ports (Seattle, Oakland, LA, Brooklyn) that would suffer the most as the
> unloading docks aren't that much above sea level.
> Oh, and you do lose most of Cape Canaveral and the JFK space center.
> But if one is willing to compensate for the rise (sea walls, land fill,
> etc.) most of the U.S. goes untouched (raising of course the problem of how
> to motivate people to be concerned). It does however look like some places,
> e.g. the Bahamas, really get creamed.
His web site has some caveats about the mapping accuracy at the
detailed level and areas outside the US.
There are a number of significant sources of inaccuracy. All of these
inaccuracies are optimistic - correcting the inaccuracy would make the
consequences of sea level rise look worse. I've made a conscious
effort to avoid ad hoc corrections for these effects. If these maps
have a purpose, it is to encourage the general public to consider the
consequences of global warming. If I were to make corrections that
make more bits of the map shaded blue, then I would run the risk of
having the whole thing discredited as alarmist.
Firstly, the model knows nothing about the tides. Since tidal
variation can be 10m or more in some parts of the world, this is a
Secondly, the NASA data itself is not very accurate. Jonathon Stott
has said that "NASA claims their height data is accurate to +/- 16m
with 90% certainty". NASA gathered the data by radar from orbit, so
buildings and trees cause a systematic overestimation of the elevation
of built-up and forested areas.
Thirdly, the NASA data does not extend beyond +/-60 degrees latitude.
Its accuracy becomes degraded at the extremes of its range, especially
in the Southern hemisphere, I am told.
Fourthly, the simulation takes no account of the effects of coastal
erosion. I believe that anywhere within a metre or so of daily maximum
sea level would be swiftly eroded. So areas which my model shows as
future 'coastline' would almost certainly be quickly eroded away.
Fifthly, I don't take any account of coastal defences. It's obviously
possible to build defences that protect habitable land far below sea
level. I've got no way of knowing whether current defences (in
Holland, say) are able to withstand an extra +1 metre of mean sea
level. I imagine that the impact would depend upon how quickly the
oceans rise, and how much money was available for building new
Finally, there are areas of the world far from the oceans that are far
below sea level. These areas are shown as flooded on my map, where
clearly they are not in danger. The area North of the Caspian Sea is
the most striking example.
If you want a detailed local view, your best bet is to look at
detailed topographical maps for your area and follow the contour
Investigating old maps is also interesting. The coastline of England
has changed a lot since the Middle Ages. Some areas have been lost to
the sea and other areas have been reclaimed.
Another point to bear in mind is that if all the ice melts, flooding
may only be a small part of the problem. The sea circulation will
probably stop, leading to huge climate change effects.
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