Why The Hay Paper On Sea Level Got It So Wrong

By Paul Homewood    

 

Further to the Hay et al paper, which claims that sea level rise must have been less during the 20thC, a reminder of another paper in 2013 by Gregory et al which came to the opposite conclusion.

just to recap, Hay et al claim that sea levels up to around 1990 could not have risen as fast as just about every study based on tidal gauges has found, which suggest around 150 to 200mm/C. Hay’s logic is that global sea temperatures were not high enough to cause enough thermal expansion, and that glacial melt was also too small.

 

The Gregory paper was written by a who’s who of marine and glacial experts, including Church, White and 18 others.

 

 

 

Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts?

 

ABSTRACT

Confidence in projections of global-mean sea level rise (GMSLR) depends on an ability to account for GMSLR during the twentieth century. There are contributions from ocean thermal expansion, mass loss from glaciers and ice sheets, groundwater extraction, and reservoir impoundment. Progress has been made toward solving the “enigma” of twentieth-century GMSLR, which is that the observed GMSLR has previously been found to exceed the sum of estimated contributions, especially for the earlier decades. The authors propose the following: thermal expansion simulated by climate models may previously have been underestimated because of their not including volcanic forcing in their control state; the rate of glacier mass loss was larger than previously estimated and was not smaller in the first half than in the second half of the century; the Greenland ice sheet could have made a positive contribution throughout the century; and groundwater depletion and reservoir impoundment, which are of opposite sign, may have been approximately equal in magnitude. It is possible to reconstruct the time series of GMSLR from the quantified contributions, apart from a constant residual term, which is small enough to be explained as a long-term contribution from the Antarctic ice sheet. The reconstructions account for the observation that the rate of GMSLR was not much larger during the last 50 years than during the twentieth century as a whole, despite the increasing anthropogenic forcing. Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors’ closure of the budget is that such a relationship is weak or absent during the twentieth century.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00319.1

 

 

So they find:

1) Thermal expansion was greater. (They speculate volcanic forcing, but surely higher global temperatures, as originally derived before all of the adjustments since, is a much more likely candidate?)

2) Glacial loss was much more than originally assumed and was not smaller in the first half of the 20thC. (Again, why the surprise? Studies of glacial loss from Alaska and the Alps, among others, have always shown that).

3) Ice loss from the Greenland ice sheet has been occurring throughout the 20thC. (Again, why the surprise? We know that temperatures in Greenland, and around much of the Arctic, were just as high in the 1930’s and 40’s as they are now).

 

The last sentence is crucial:-

Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors’ closure of the budget is that such a relationship is weak or absent during the twentieth century.

 

Translation – there is little evidence of any relationship between GMSLR and “global climate change”.  All we have been seeing is a natural rise in sea levels following the Little Ice Age, during which, according to climatologists such as HH Lamb, sea levels fell.