New paper: Global sea level linked to global temperature

Global sea level linked to global temperature
By Martin Vermeera, and Stefan Rahmstorf
October 26, 2009
http://www.pnas.org/content/106/51/21527.full.pdf

This new paper takes a 'modern' look at sea level rise projections out to 2100 AD.

The abstract notes:
"For future global temperature scenarios of the Intergovernmental Panel on Climate Change’s Fourth Assessment Report, the relationship projects a sea-level rise ranging from 75 to 190 cm for the period 1990–2100"

In the discussion on projections of future sea levels:-
"Qualitatively we consider this decline in the thermal share and increasing importance of ice melt a robust result, which is our key difference to the IPCC AR4 (2), where the ice-melt share is assumed to diminish with thermal expansion contributing between 55% and 70% of the total sea-level rise over the 21st century."

which fits well with my albeit uneducated perspective,

In
Discussion: Implications for the Future
If our method presents a reasonable approximation of the future sea-level response to global warming, then for a given emission scenario sea level will rise approximately three times as much by 2100 as the projections (excluding rapid ice flow dynamics) of the IPCC AR4 (2) have suggested. Even for the lowest emission scenario (B1), sea-level rise is then likely to be [about] ~1 m; for the highest, it may even come closer to 2 m.

Uncertainties remain, however..."

The discussion concludes:

"In addition, highly nonlinear responses of ice flow may become increasingly important during the 21st century. These are likely to make our linear approach an underestimate. Therefore, we have to entertain the possibility that sea level could rise faster still than suggested by the simple projection based on Eq. 2.

How much faster? Pfeffer et al. (25) provided an independent estimate of maximum ice discharge based on geographic constraints on ice flow; they concluded that sea-level rise in the 21st century is very unlikely to exceed 200 cm. If this estimate is correct, a nonlinear dynamical ice-sheet response may not change our estimate upward by very much. To limit global sea-level rise to a maximum of 1 m in the long run (i.e., beyond 2100), as proposed recently as a policy goal (26), deep emissions reductions will be required. Likely they would have to be deeper than those needed to limit global warming to 2 °C, the policy goal now supported by many countries. Our analysis further suggests that emissions reductions need to come early in this century to be effective.""

--

and still...
ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_mm_mlo.txt
Seasonally corrected March 2010 level of CO2 = 389.44ppm, and so based on the average rate of change over the last three months, its probably about 389.73ppm today, and still rising....

Now: Why it's even worse than we feared.

In relation to the Science behind my estimates of sea level rise we can now add the information from an article by Sharon Begley at newsweek.com published 24 July 2009. Sharon pulls together some recent views on the state of the ice on and around Greenland. Read the article for the details.

http://www.newsweek.com/id/208164

Some quotes:

...the sea ice found a more open, ice-free, and thus faster path westward thanks to Arctic melting.

...The loss of Arctic sea ice "is well ahead of" what the Intergovernmental Panel on Climate Change forecast, largely because emissions of carbon dioxide have topped what the panel—which foolishly expected nations to care enough about global warming to do something about it—projected. "The models just aren't keeping up" with the reality of CO2 emissions, says the IPY's David Carlson.

... satellite measurements of Greenland's mass, show that it is losing about 52 cubic miles per year and that the melting is accelerating. So while the IPCC projected that sea level would rise 16 inches this century, "now a more likely figure is one meter [39 inches] at the least," says Carlson. "Chest high instead of knee high, with half to two thirds of that due to Greenland." Hence the "no idea how bad it was."

...estimates of how much carbon is locked into Arctic permafrost were, it turns out, woefully off. "It's about three times as much as was thought, about 1.6 trillion metric tons, which has surprised a lot of people," says Edward Schuur of the University of Florida. "It means the potential for positive feedbacks is greatly increased." That 1.6 trillion tons is about twice the amount now in the atmosphere. And Schuur's measurements of how quickly CO2 can come out of permafrost, reported in May, were also a surprise: 1 billion to 2 billion tons per year. Cars and light trucks in the U.S. emit about 300 million tons per year.

...the G8, led by Europe, has vowed to take steps to keep global warming below 2 degrees Celsius by reducing CO2 emissions. We're now at 0.8 degree. But the amount of CO2 in the atmosphere is already enough to raise the mercury 2 degrees. The only reason it hasn't is that the atmosphere is full of crap (dust and aerosols that contribute to asthma, emphysema, and other diseases) that acts as a global coolant. As that pollution is reduced for health reasons, we're going to blast right through 2 degrees, which is enough to ex-acerbate droughts and storms, wreak havoc on agriculture, and produce a planet warmer than it's been in millions of years.

...The test of whether the nations of the world care enough to act will come in December, when 192 countries meet in Copenhagen to hammer out a climate treaty. Carlson vows that IPY will finish its Arctic assessment in time for the meeting, and one conclusion is already clear. "A consensus has developed during IPY that the Greenland ice sheet will disappear," he says.

Now what happens to Greenland will also be mirrored in the Antartic, where as detailed in previous posts and below, the West Antarctic Ice Sheet is showing signs of distress. The combination serves to push the "Very Likely" sea level rise closer to two metres, and the possible worst case through my estimated five metres.

I insure my house against fire for the possible worst case. I don't know anybody who has had their house burned down, do you? But we all act to protect ourselves and our record collections against the conceivable worst case. Five metres is conceivable, and even more so in terms of these latest discoveries by the International Geophysical Year scientists.

We should act accordingly.