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]
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...]
The Multivariate ENSO Index (MEI) is the unrotated, first principal component of six observables measured over the tropical Pacific (see NOAA ESRL MEI, Wolter & Timlin, 1993,1998). To compare the global mean sea level to the MEI time series, we removed the mean, linear trend, and seasonal signals from the 60-day smoothed global mean sea level estimates and normalized each time series by its standard deviation. The normalized values plotted above show a strong correlation between the global mean sea level and the MEI, with the global mean sea level often lagging changes in the MEI. Since the MEI has recently sharply increased (coming out of a strong La Niña), we expect the global mean sea level estimates to also reverse their recent downward trend and begin to increase as the La Niña effects wane.
[Update, 2011/06/20: Media Matters has published a story on the attention our GIA correction has received.]
Regarding the Fox News article by Maxim Lott (derived from previous blogs, e.g., Heartland Institute/Forbes) that questions our application of the glacial isostatic adjustment (GIA) correction to the altimeter-based global mean sea level (GMSL) time series and rate estimates, we would like to direct interest to our Frequently Asked Questions (FAQ) page that discusses the GIA effect and also the differences between our global mean sea level estimates from altimetry and regional/local relative sea level measured by tide gauges. These FAQs were updated in May with content partially derived from the discussion with Mr. Maxim, but much of this important content unfortunately did not get published in the Fox News article or in recent blogs.
We would also suggest consulting the other unaffiliated sea level research groups around the world that independently estimate global mean sea level from altimetry and also apply the scientifically well-understood GIA correction. Their current GMSL rate estimates are listed on the left sidebar of our site for reference. Note that our current rate estimate is actually the lowest of the groups, which does not support the claim that we "doctor the sea level data" to artificially support pro-climate change opinions. Instead, we strive to produce estimates of the global mean sea level time series and rate using the best available information to address the following questions:
- How is the volume of the ocean changing?
- How much of this is due to thermal expansion?
- How much of this is due to addition of water that was previously stored as ice on land?
As the science of sea level change becomes better understood through peer-reviewed research, we include these advances in our global mean sea level estimates. This includes continuously improving some our applied altimetry corrections, such as better satellite orbits, ocean tides, and sea state bias models (all of which, along with the GIA correction, were updated and documented in our last 2011_1 release). For further study, we encourage interested parties to consult the references supplied in the FAQs and cataloged in our library and to also contact other research groups and scientists specifically studying global and regional sea level change.