Friday 8 September 2017

Indicators of global climate change are detected in tropical oceans


Researchers from the University of California, Irvine and NASA's Jet Propulsion Laboratory have reported the first observation of sea level "fingerprints," tell-tale differences in sea level rise around the world in response to changes in continental water and ice sheet mass. The team's findings were published in the American Geophysical Union journal Geophysical Research Letters.

Indicators of global climate change are detected in tropical oceans
"Scientists have a solid understanding of the physics of sea level fingerprints, but we've never had a direct detection 
of the phenomenon until now," says study co-author Isabella Velicogna, a UCI professor of Earth system science
 and Jet Propulsion Laboratory research scientist, shown here on an expedition to Greenland 
[Credit: Maria Stenzel/UCI]
"Scientists have a solid understanding of the physics of sea level fingerprints, but we've never had a direct detection of the phenomenon until now," said co-author Isabella Velicogna, UCI professor of Earth system science and JPL research scientist.

As ice sheets and glaciers undergo climate-related melting, they alter Earth's gravity field, which causes nonuniform sea level change. Certain regions, particularly in the middle latitudes, are harder hit. For instance, Antarctica-generated sea level rise in California and Florida is as much as 52 percent greater than what's average in the rest of the world.

Indicators of global climate change are detected in tropical oceans
Cumulative sea level fingerprints calculated from observations of Greenland, Antarctica, glaciers 
and ice caps and land water storage mass changes observed with the GRACE satellites for the time
 period January 2003 to April 2014 [Credit: Isabella Velicogna & Chia-Wei Hsu/UCI]
The team calculated sea level fingerprints using time-variable gravity data collected by the twin satellites of NASA's Gravity Recovery & Climate Experiment between April 2002 and October 2014. During that time, according to the study, the global mean sea level grew by about 1.8 millimeters per year, with 43 percent of the increased water mass coming from Greenland, 16 percent from Antarctica, and 30 percent from mountain glaciers. The scientists verified their calculations of sea level fingerprints associated with these mass variations via ocean-bottom pressure readings from stations in the tropics.

Indicators of global climate change are detected in tropical oceans
Sea level fingerprints in millimeters per year calculated from observations of the mass loss of Greenland, 
Antarctica, glaciers and ice caps and changes in land water storage using time-variable gravity data collected 
by the twin satellites of the U.S./German Gravity Recovery and Climate Experiment mission between April 2002 
and October 2014. The blue contour (1.8 mm/year) is the average sea level rise if the total addition of mass 
of water to the ocean was spread uniformly over the world’s oceans. The SLF are not uniform and bulge
 around the equatorial regions [Credit: Isabella Velicogna & Chia-Wei Hsu/UCI]
"It was very exciting to observe the sea level fingerprints in the tropics, where they were not expected to be detectable," said lead author Chia-Wei Hsu, a graduate student researcher at UCI. "In the tropics, sea level fingerprint values are very close to global average sea level values, making them harder to detect."

Velicogna added: "We know that sea levels climb faster in the middle to low latitudes versus the high latitudes and that Greenland and Antarctica contribute differently to the process. With our improved understanding through GRACE data and other techniques, we're now able to take any point on the global ocean and determine how much the sea level there will rise as a result of glacier ice melt."

Source: University of California - Irvine [September 08, 2017]

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