New study using GRACE data shows global sea levels rising less than 7 inches per century

Finds sea levels have risen over the past 9 years [2002-2011] at a rate of only 1.7 mm/yr, equivalent to 6.7 inches per century, matching tide gauge data rates.

The paper corroborates the NOAA 2012 Sea Level Budget which finds sea levels have risen at only 1.1-1.3 mm/yr over the past 7 years from 2005-2012 [less than 5 inches/century], and the paper of Chambers et al finding “sea level has been rising on average by 1.7 mm/year over the last 110 years.” 

From the IPCC FAR Chapter 5.5.2: Holgate and Woodworth (2004) estimated a rate of 1.7 ± 0.4 mm yr^–1 sea level change averaged along the global coastline during the period 1948 to 2002, based on data from 177 stations divided into 13 regions. Church et al. (2004) (discussed further below) determined a global rise of 1.8 ± 0.3 mm yr^–1 during 1950 to 2000, and Church and White (2006) determined a change of 1.7 ± 0.3 mm yr^–1 for the 20th century.

The paper:

Impact of Continental Mass Change on Rate-of-Rise of Sea Level

Present-day continental mass variation as observed by space gravimetry reveals secular mass decline and accumulation. Whereas the former contributes to sea-level rise, the latter results in sea-level fall. As such, consideration of mass accumulation (rather than focussing solely on mass loss) is important for reliable overall estimates of sea-level change. Using data from the Gravity Recovery And Climate Experiment satellite mission, we quantify mass-change trends in 19 continental areas that exhibit a dominant signal. The integrated mass change within these regions is representative of the variation over the whole land areas. During the integer 9-year period of May 2002 to April 2011, GIA-adjusted mass gain and mass loss in these areas contributed, on average, to -(0.7 ± 0.4) mm/year of sea-level fall and + (1.8 ± 0.2) mm/year of sea-level rise; the net effect was + (1.1 ± 0.6) mm/year. Ice melting over Greenland, Iceland, Svalbard, the Canadian Arctic archipelago, Antarctica, Alaska and Patagonia was responsible for + (1.4±0.2) mm/year of the total balance. Hence, land-water mass accumulation compensated about 20 % of the impact of ice-melt water influx to the oceans. In order to assess the impact of geocentre motion, we converted geocentre coordinates derived from satellite laser ranging (SLR) to degree-one geopotential coefficients. We found geocentre motion to introduce small biases to mass-change and sea-level change estimates; its overall effect is + (0.1 ± 0.1) mm/year. This value, however, should be taken with care owing to questionable reliability of secular trends in SLR-derived geocentre coordinates.

A slide show on the paper is available here: Baur_GGHS2012

Reference

Baur, O., Kuhn, M. and Featherstone, W.E. 2013. Continental mass change from GRACE over 2002-2011 and its impact on sea level. Journal of Geodesy 87: 117-125.

Background

The authors write that “present-day continental mass variation as observed by space gravimetry reveals secular mass decline and accumulation,” and that “whereas the former contributes to sea-level rise, the latter results in sea-level fall.” Therefore, they state that “consideration of mass accumulation (rather than focusing solely on mass loss) is important for reliable overall estimates of sea-level change.”

What was done

Employing data derived from the Gravity Recovery And Climate Experiment – the GRACE satellite mission – Baur et al. assessed continental mass variations on a global scale, including both land-ice and land-water contributions, for 19 continental areas that exhibited significant signals. This they did for a nine-year period (2002-2011), which included “an additional 1-3 years of time-variable gravity fields over previous studies.” And to compensate for the impact of glacial isostatic adjustment (GIA), they applied the GIA model of Paulson et al. (2007).

What was learned

Over the nine years of their study, the three researchers report that the mean GIA-adjusted mass gain and mass loss in the 19 areas of their primary focus amounted to -(0.7 ± 0.4 mm/year) of sea-level fall and +(1.8 ± 0.6) mm/year of sea-level rise, for a net effect of +(1.1 ± 0.6) mm/year. Then, to obtain a figure for total sea-level change, they added the steric component of +(0.5 ± 0.5) mm/year, which was derived by Leuliette and Willis (2011), to their net result to obtain a final (geocenter neglected) result of +(1.6 ± 0.8) mm/year and a final (geocenter corrected) result of +(1.7 ± 0.8) mm/year.

What it means

The final geocenter-corrected result of Baur et al. is most heartening, as Chambers et al. (2012) indicate that “sea level has been rising on average by 1.7 mm/year over the last 110 years,” as is also suggested by the analyses of Church and White (2006) and Holgate (2007). Concomitantly, the air’s CO2 concentration has risen by close to a third. And, still, it has not impacted the rate-of-rise of global sea level!

References

Chambers, D.P, Merrifield, M.A. and Nerem, R.S. 2012. Is there a 60-year oscillation in global mean sea level? Geophysical Research Letters 39: 10.1029/2012GL052885.

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.

Paulson, A., Zhong, S. and Wahr, J. 2007. Inference of mantle viscosity from GRACE and relative sea level data. Geophysical Journal International 171: 497-508.

This essay was derived from several sources: CO2Science.org, The Hockey Schtick, and independent located content.