This story says that if global warming continues, by 2020, three major (coastal) Indian cities could be completely submerged.
http://www.ess.co.at/GAIA/CASES/IND/BOM/BOMmain.html
http://www.iclei.org/economy/conference/abstracts/A4_1.pdf
http://www.chennai.tn.nic.in/chndistprof.htm
Yup, looks pretty plausible to me.
2020 is way too soon for complete submersion. But large areas of those cities will be underwater under “ideal” conditions for periods of time. E.g., strong onshore winds, waterlogged soils and neap tides. Add another 40-60 years to get complete submersion. (You should also check the elevations of any property you own near the shore. If they are too low, they won’t be going up in price. Sell now, buy higher up.)
It is turning out to be very hard to predict sea level changes because the rate of temp. change is increasing faster than models have predicted. Once the Arctic Ocean is ice free during the summer, watch out.
There are numerous cities that will face the same problem, e.g., Venice (which is already having troubles unrelated to global warming), but the problem extends well beyond that. Many Pacific Island nations, located on small islands no more than a few meters above the current global mean sea level, will have to deal with the relocation of their entire populations. And frankly, the better part of Bangladesh, already overwhelmed on a regular basis by normal weather patterns, will be permanently inundated. Politically, the “death” of inundated nations and the climate refugee problem will be a thorny issue, but it’s seldom mentioned in popular discussions of the effects of global warming.
By the way, this statement
is incorrect. Melting of sea ice in the Arctic Ocean will not have any effect on mean global sea level, simply because the ice is already in the water and melting won’t add to ocean volume. Melting of ice sheets on Greenland and Antarctica, on the other hand, will have a significant impact on sea level because ice/water mass are transferred from land to the ocean. Should the West Antarctic ice sheet collapse, for example, global mean sea level will rise on the order of 6 meters.
It’s true though that global mean sea level needn’t rise very much for coastal cities to run into flooding problems on a regular basis. Changing weather patterns related to global warming may include more frequent and/or stronger storms that could make it very expensive to try to protect coastal properties.
[slight hijack & mild rant] No one should be building right next to beaches any more, and most certainly not on barrier islands. Beaches and barrier islands are geologically ephemeral features, capable of changing significantly in less than a few decades’ time, sometimes with the help of just one strong hurricane or winter storm. The ridiculous practice here in the U.S. of building jetties and piping in sand to rebuild beaches, meant to protect property values, is a tremendous waste of taxpayer resources that’s about as useful as whistling into the wind and hoping to change the wind direction. [/slight hijack & mild rant]
That would mean that we need to have over an 11m increase in sea level in the next twenty years. Not even the worst case scenarios allows for such a rapid rise.
Since water is more dense than ice, couldn’t it actually make the sea levels go down?
There is very little science behind these global warming scenarios…In 20 years not a single city will be wiped out due to “global warming”. It’s time to get a life people…Marcus
To completely submerge, yes.
How is mean sea-level calculated? Coz I’m from Bombay and believe me, the water won’t have to climb anywhere near 11m to submerge most of the “downtown” areas. More like half a metre.
That’s true. Estimates of how quickly global mean sea level will rise vary, partly because we aren’t certain how the increase in global mean temperature will proceed (speed up? slow down? remain at the current rate? role of anthropomorphic contributions vs. natural feedbacks? etc.), and partly because we aren’t certain just how natural systems will respond (e.g., will the West Antarctic ice sheet collapse or not, and if so, to what extent?). The most recent estimate released by the Intergovernmental Panel on Climate Change (IPCC) is 49 cm over the next hundred years, with an uncertainty of 20-86 cm. A more conservative estimate suggests a sea level rise of between 6-30 cm by 2130 AD.
Also keep in mind that that actual sea level rise in any given location is the combined result of changes in global ocean volume (through added water, thermal expansion) and local conditions (e.g., local response of river deltas to the increased mass of water sitting above them), which is why predictions for specific locations can be more difficult to determine.
This link is from an environmentally oriented site, but it is a nice summary of the more recent reports out of the IPCC. runinout, I strongly suggest that you do some reading - there is in fact a helluva lot of science going into studying climate change and the future impact of global warming. A search of GQ and GD will help get you started, because this topic has come up numerous times since I started lurking on this board.
Well in this case, the decrease in volume owing to the density contrast between ice and water is likely going to be muffled by thermal expansion of the water as a result of warming. I don’t think you can say that melting sea ice will have an overall positive (for people) effect on global mean sea level.
Global mean sea level used to be calculated by looking at long-term tidal gauge records in different locations. These days, such tidal data are combined with satellite data to calculate mean sea level to an impressively high degree of precision. A Google search on “global mean sea level” will get you plenty of links to the various organizations that contribute to the calculations.
And yes, mean elevations for cities don’t tell the whole story re: safety from mean sea level rise. New York City has a mean elevation of about 55 ft. (over 16 m), but I’m sure that would be cold comfort to the residents of Battery Park City when they have to start taking a ferry rather than the subway uptown. 
Runinout: funny, you’re the only person who hasn’t backed up your position… care to post some references?
This page has a nice summary of the impacts of accelerated sea level rise in general and on certain coastal areas in particular (and yes, Bombay is one of the vulnerable places mentioned).
For U.S. dopers, an assessment of coastal vulnerabilities. Flooding problems will impact Boston, New York, Charleston, Miami and New Orleans in particular.
Brief news item on vulnerabilities in Europe.
Reports issued by the IPCC can be found here.
I did not say that having the Arctic ice free in summer would directly increase sea levels. I’m not an idiot, I know ice floats, etc. Sheesh.
I definitely did say something very technically correct: When the Arctic is ice free for a good chunk of the year, the warming situation will change dramatically. Open water doesn’t reflect light nearly as well as ice. This will be a serious effect.
A friend of mine, who is always in a stae of wild-eyed panic, has this to say. The most immediate danger is contamination of ground water. Apparently he is talking about the salt and other minerals in sea water.
How immediate is this danger, if real at all? And what would the effect likely be?
True Blue Jack
- It’s about as dangerous as “global warming” itself.
- Don’t panic.
http://water.usgs.gov/ogw/gwrp/saltwater/links.html
http://ga2.er.usgs.gov/coastal/coastalreport.cfm
It has to do with seawater forcing itself into ground water in places that are right by the sea. Where does your friend live?
Sorry to have misunderstood you. I have heard people say that melting sea ice would directly impact sea level - on these very boards, even - and I thought you meant the same.
As for albedo effects (the reflectance of sunlight from the Earth’s surface) - yes, sea water does have a lower albedo than land and much lower than sea ice. However, at latitudes above the Arctic Circle, the impact of decreased albedo is less than you might think because average annual amount of solar radiation striking the Earth’s surface at high latitudes is significantly less than in the tropics and mid-latitudes. (See this page for a brief discussion on solar radiation and calculating the amount of solar radiation that reaches the Earth’s surface.)
Where an ice-free Arctic Ocean would have an impact is on regional climate patterns in the very least (e.g., increased precipitation, stronger storms). There is also the possibility that broader impacts could be felt if patterns of ocean circulation in the North Atlantic are disrupted, but at the moment climate models are not in agreement as to the severity and extent of such disruptions. A fresh water pulse disrupting the Gulf Stream is one thing that does come up frequently, and it certainly would have a negative impact on Europe’s weather.
This page has a nice explanation of the interactions between freshwater and salt water in aquifers along a coastline. If your friend lives along the coast, True Blue Jack, it might well be a concern for him, but it most certainly won’t be the only one - greater exposure to damaging storms and increased erosion on the shoreline will likely catch his attention first.
DDG, the problem of salt-water incursion is a very real one, albeit not necessarily related to global warming issues (see my link in this post). Your own links point that out. What’s the point of your two “points”?
Errr…I didn’t answer Jack’s questions? 
Q. “How immediate is this danger?”
A. “It’s about as dangerous as global warming itself.”
Q. “What will the effect likely be?”
A. “Don’t panic”. Link to most informative USGS Page O’ Links to other sites dealing with the phenomenon.
There were two assumptions inherent in my post:
A. That Jack is smart enough to understand that “global warming” doesn’t mean he has to pack his bags and flee for higher ground just yet.
B. That Jack is smart enough to click on a provided link to see what it says.
Where did I say that saltwater incursion was not a real problem?
Rising sea levels, directly, are equally harmful to all the big US coastal plain cities. But most of them do not get their water from aquifers. E.g., NYC gets its water from far off dams with really, really big pipes. They won’t be affected aquifer-wise.
But Florida, for example, doesn’t have any mountainous terrain where they can build dams, etc. So they depend a lot on aquifers, which are also made of quite porous stone. These are being rapidly damaged anyway from excess pumping, so rising sea levels will just speed up the process of “time to get water some other way.” Most of the Gulf States’s coastal regions are in the same boat. There are more rivers to tap into, but that water is surprisingly (!) Not Good To Drink.
Coastal regions from VA to GA are also going to have problems. They will have better access to inland sources, but there are already people using those. “Water wars” like you see out west will be a big problem.
On the US west coast. In the drier areas, there isn’t enough groundwater to begin with so they’ve been importing water for decades. In the wetter areas, there’s a lot more mountain runoff so that wells usually aren’t a primary resource (on the coast).