2010/04/18

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.""

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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....

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