Volume 13, Number 4: 27 January 2010
"Global mean sea level change," in the words of Leuliette and Miller (2009), "results from two major processes that alter the total volume of the ocean." These processes are (1) changes in total heat content and salinity, which produce density or steric changes, and (2) the exchange of water between the oceans and other reservoirs (such as glaciers, ice caps and ice sheets, plus land-based liquid water reservoirs), which result in mass variations. And in regard to these several components, they note that although satellite radar altimeters have provided global observations since the early 1990s, only since 2002 have satellite gravity observations allowed for global estimates of mass variations, and not until 2007 had the Argo Project achieved its goal of 3000 floats measuring truly global steric changes.
Using appropriate data to see if the sum of global steric and global mass contributions to global sea level rise were indeed equal to the observed global sea level rise (within the error bounds of each side of the equation), two prior attempts to close the global sea level rise budget were performed by Lombard et al. (2007) and Willis et al. (2008). Both of these attempts, however, were unsuccessful. Consequently, and with a little more data, Leuliette and Miller attempted to obtain closure (and, therefore, greater confidence in the final result) one more time.
The two U.S. researchers say their "new analysis of the sea level rise budget for the period January 2004 to December 2007 used corrected Jason-1 and Envisat altimetry observations of total sea level, improved upper ocean steric sea level [data] from the Argo array, and ocean mass variations inferred from GRACE gravity mission observations." This effort yielded success, as they closed the global sea level rise budget by finding that the sum of steric sea level and ocean mass components had a trend of 1.5 ± 1.0 mm/year over the period of their analysis, which they state is "in agreement with the total sea level rise observed by either Jason-1 (2.4 ± 1.1 mm/year) or Envisat (2.7 ± 1.5 mm/year) within a 95% confidence interval."
Of course, there is still the question of which of the three mean results lies closest to the truth, which is of great importance, since the last of the three results is fully 80% greater than the first. In this regard, we note that Woppelmann et al. (2009) recently obtained a result of 1.58 ± 0.03 mm/year, by analyzing GPS observations from a global network of 227 stations over the period January 1997 to November 2006; and they cite a result of 1.7 mm/year obtained by both Church and White (2006) and Holgate (2007).
All in all, it would appear that researchers are gradually closing in on the truth (if they are not essentially already there); and that truth suggests that we are not yet seeing any of the catastrophic sea level rise that is so highly hyped by both Al Gore and James Hansen.
Sherwood, Keith and Craig Idso
Reference
Church, J.A. and White, N.J. 2006. A 20th century acceleration in global sea-level rise. Geophysical Research Letters 33: 10.1029/2005GL024826.
Holgate, S.J. 2007. On the decadal rates of sea level change during the twentieth century. Geophysical Research Letters 34: 10.1029/2006GL028492.
Leuliette, E.W. and Miller, L. 2009. Closing the sea level rise budget with altimetry, Argo, and GRACE. Geophysical Research Letters 36: 10.1029/2008GL036010.
Lombard, A., Garcia, D., Ramillien, G., Cazenave, A., Biancale, R., Lemoine, J., Flechtner, F., Schmidt, R. and Ishii, M. 2007. Estimation of steric sea level variations from combined GRACE and Jason-1 data. Earth and Planetary Science Letters 254: 194-202.
Willis, J.K., Chambers, D.P. and Nerem, R.S. 2008. Assessing the globally averaged sea level budget on seasonal to interannual timescales. Journal of Geophysical Research 113: 10.1029/2007JC004517.
Woppelmann, G., Letetrel, C., Santamaria, A., Bouin, M.-N., Collilieux, X., Altamimi, Z., Williams, S.D.P. and Miguez, B.M. 2009. Rates of sea-level change over the past century in a geocentric reference frame. Geophysical Research Letters 36: 10.1029/2009GL038720.