Humans optimistically believe that populations and economies will continue to grow without limit for centuries to come. The history of the Earth begs to differ. There is consistent relationship between between CO2 concentrations and sea level which can not be ignored. Greenhouse gas concentrations like those we have now (almost 400 parts per million) are systematically associated with sea levels at least 9 meters (28.5 feet) above current levels.
By comparing reconstructions of atmospheric CO2 concentrations and sea level over the past 40 million years, researchers based at the National Oceanography Centre, Southampton have found that greenhouse gas concentrations similar to the present (almost 400 parts per million) were systematically associated with sea levels at least nine metres above current levels.
[image left: New York City as envisioned after a mere 3 meter rise in sea level.]
[My note: The CO2 level in the atmosphere is currently 393/394 ppm (parts-per-million) in the atmosphere.]
The study determined the ‘natural equilibrium’ sea level for CO2 concentrations ranging between ice-age values of 180 parts per million and ice-free values of more than 1,000 parts per million.
It takes many centuries for such an equilibrium to be reached, therefore whilst the study does not predict any sea level value for the coming century, it does illustrate what sea level might be expected if climate were stabilized at a certain CO2 level for several centuries.
Lead author Dr Gavin Foster, from Ocean and Earth Science at the University of Southampton which is based at the centre, said, “A specific case of interest is one in which CO2 levels are kept at 400 to 450 parts per million, because that is the requirement for the often mentioned target of a maximum of two degrees global warming.”
The researchers compiled more than two thousand pairs of CO2 and sea level data points, spanning critical periods within the last 40 million years. Some of these had climates warmer than present, some similar, and some colder. They also included periods during which global temperatures were increasing, as well as periods during which temperatures were decreasing...
The researchers found that the natural relationship displays a strong rise in sea level for CO2 increase from 180 to 400 parts per million, peaking at CO2 levels close to present-day values, with sea level at 24 +7/-15 metres above the present, at 68 per cent confidence limits.
Although it has taken "many centuries" for a CO2/sea level equilibrium to be reached during the last 40 million years, that delay doesn't mean that New York City is off the hook. Consider this graph from The Observed Increase in Oceanic and Atmospheric CO2 and an Outlook for the Future by Pieter Tans, published in the journal Oceanography in December, 2009 (pdf).
Note: Not all emitted carbon dioxide goes into the atmosphere. Some of it is absorbed by the oceans, which leads to ocean acidification, and some of it is taken up by the terrestrial carbon sink (photosynthetic biomass). Thus total emissions are higher than shown in this graph (left scale). CO2 persists in the atmosphere long after anthropogenic emissions start declining.
Although for various reasons I incline to Scenario A, which shows emissions peaking well before 2050, this less "dire" scenario for atmospheric CO2 also shows that carbon dioxide in the atmosphere remains above or near 400 ppm for five centuries after the peak. I'm guessing that's enough time for sea levels to stabilize at (at least) 9 meters above the current level. Even if I miss my guess, that should certainly be enough time for the sea to rise 5-6 meters on the way to an even bigger flood.
Therefore, we are entitled to conclude that sometime in the coming five centuries, and probably sooner rather than later, depending on how the Greenland and West Antarctic ice sheets respond to the warming, The City That Never Sleeps will be toast. The Big Apple is going to become the Big Moose Pie. Looking on the bright side, such sea level rise will certainly also wipe out Washington D.C., which I think we can all agree would be a good thing
But don't despair, you future citizens of Gotham. All is not lost. How about underwater nightclubs?