Blogs

NASA mission takes stock of Earth's melting land ice

Edited: 2015-05-04

NASA mission takes stock of Earth's melting land ice - In the first comprehensive satellite study of its kind, a University of Colorado at Boulder-led team used NASA data to calculate how much Earth's melting land ice is adding to global sea level rise. [NASA Climate News]

NASA Satellites Detect Pothole on Road to Higher Seas

Edited: 2015-05-20

Our colleagues at JPL have also been interested in how the global mean sea level is affected by the ENSO (i.e., El Niño and La Niña).  They find that GRACE measurements helped to identify the distribution of abnormally high rainfall over land resulting from the recent strong La Niña.  This temporary transfer of large volumes of water from the oceans to the land surfaces also helps explain the large drop in global mean sea level. But they also expect the global mean sea level to begin climbing again.

An Update from NASA's Sea Level Sentinels:

Like mercury in a thermometer, ocean waters expand as they warm. This, along with melting glaciers and ice sheets in Greenland and Antarctica, drives sea levels higher over the long term. For the past 18 years, the U.S./French Jason-1, Jason-2 and Topex/Poseidon spacecraft have been monitoring the gradual rise of the world's ocean in response to global warming.

While the rise of the global ocean has been remarkably steady for most of this time, every once in a while, sea level rise hits a speed bump. This past year, it's been more like a pothole: between last summer and this one, global sea level actually fell by about a quarter of an inch, or half a centimeter.

So what's up with the down seas, and what does it mean? Climate scientist Josh Willis of NASA's Jet Propulsion Laboratory, Pasadena, Calif., says you can blame it on the cycle of El Niño and La Niña in the Pacific. [Read more...]

GMSL Updated and Compared to MEI

Edited: 2011-07-29

We recently updated the global mean sea level time series through Jason-2 cycle 102.  In this release, we updated the sea state bias model (SSB) for TOPEX to the CLS Collinear v. 2009 model (Jason-1 and Jason-2 were already updated to this same model in 2011_rel1). Additionally, we replaced the classical inverted barometer correction with the improved AVISO Dynamic Atmopshere Correction (DAC) for all missions. Although the latest Jason-2 GMSL estimates are well below the trend line, the rate increased slightly from 3.1 to 3.2 mm/yr due to the improvements to the TOPEX SSB model and replacement of the classical IB correction with the improved DAC correction.

We also began comparing the GMSL time series to the Multivariate ENSO Index since previous studies have shown that GMSL and ENSO changes are correlated. From the quick comparison, changes in the MEI tend to lead changes in the GMSL. Therefore, as the recent strong La Niña wanes, we expect the recent drop in GMSL to reverse and begin increasing (following the MEI reversal). We will continue investigating this in more detail.

GIA FAQ Updated with Peltier Reference

Edited: 2011-07-29

Regarding the glacial isostatic adjustment (GIA) correction, Professor Dick Peltier, Director of the Centre for Global Change Science at the University of Toronto and one of the leading experts on GIA and its effects on sea level, sent us the initial reference for the GIA correction that we apply to the global mean sea level estimate. The GIA FAQ and 2011_1 release notes have been updated with this reference. Here is Prof. Peltier's view on our applying the GIA correction and the recent attention it has received (hyperlinks added by us):

"...the upward correction of 0.3 mm/yr to the rate of sea level rise being measured by the altimetric satellites Topex/Poseidon and Jason-1 is a correction that was first pointed out as necessary by myself. The initial reference in which this was noted is the following:

Peltier, W.R., 2001, Global glacial isostatic adjustment and modern instrumental records of relative sea level history, on page 80 in chapter 4 of the book Sea level Rise:History and Consequences, Bruce C. Douglas, Michael S. Keaney and Stephen R. Leatherman eds, Academic Press, volume 75 in the International Geophysics Series.

The result was most recently reconfirmed in the following two papers:

Peltier, W.R. and Luthcke, S.B., 2009, On the origins of earth rotation anomalies: new insights on the basis of both "paleogeodetic" data and Gravity Recovery and Climate Experiment (GRACE) data. J. Geophys. Res. 114, B11405, doi:10.1029/2009JB006352.

Peltier, W.R., 2009. Closure of the budget of global sea level rise over the GRACE era. Quat. Sci. Rev., doi:10.1176/2009JCL12481.1 


The physical reason for the necessity of this adjustment to the atimetric satellite measurements of global sea level rise is due to the fact that, due to the large mass of water that was added to the ocean basins during the last deglaciation event of the Late Quaternary ice-age, the ocean basins are continuing to subside of average by this amount.

I'm assuming that the adjustment that Nerem has been making to his analysis of the satellite altimetry observations is this adjustment that I have previously shown to be required. Presumably he has referenced my original papers in deciding to inlcude. It has always been inlcuded in the analyses being perfomed by the group of Anny Cazenave who is the leading European scientist working in this area.

There should be nothing controversial about the necessity of making this correction. Since the need of it was established 10 years ago I'm surprised that it should be attracting attention!"
-- Dick Peltier, June 19, 2011
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