NCAR Report: Australia's Unique Influence on Global Sea Level in 2010–2011

A latest study claimed that excessive precipitation over Australia in 2010 and 2011 resulted in fall of ocean level globally.

Created On: Aug 22, 2013 17:20 ISTModified On: Aug 23, 2013 12:34 IST

A study titled Australia's Unique Influence on Global Sea Level in 2010–2011 conducted by the National Center for Atmospheric Research (NCAR) revealed that the world’s ocean level has dropped measurably, due to the excessive precipitation over Australia in 2010 and 2011. The excessive perspiration was the result coming together of the three atmospheric patterns over the Indian and Pacific Oceans.  Whereas, the soil and topographical conditions of Australia prevents running off of almost all perspiration into the ocean. As per the report, the long term trend of rise in the sea-levels due to rise in temperature resulting in melting of ice sheets at poles was temporarily halted during 2010-11. The process continued for over a period of 18 months from 2010 during which the level of oceans dropped by 7 millimeters (which is more that annual rise of water i.e. 3 millimeters).

Apart from this, at present more rain is falling over the tropical oceans as a result of which the seas are rising and this has happened due to the snapping back of the atmospheric patterns.  

Recent trend of Rise in Ocean Water

As per the latest reports, the warming of earth has caused rise in the level of ocean water by 3 millimeter annually in past few decades. The rise in the level of sea was caused due to two reasons (a) heat causes water to expand, and (b) water runoff from retreating glaciers and ice sheets.

A research paper published in 2012 prepared by Fasullo and his co-authors demonstrated the reason for increased rainfall over the tropical continents. They credited La Nina, an atmospheric oscillation as a reason for suppressed rainfall. La Niña cooled tropical surface waters in the eastern Pacific and suppressed rainfall in the region. It also enhanced it over other portions of the tropical Pacific, Africa, South America, and Australia.

To prove transformation in the landscape of Australia due to heavy rains, scientists used two different NASA satellite images of floodplains in Southwestern Queensland. The two images provide a clue towards the fall of the ocean level globally (for time being). The two images were taken on different dates, September 2009 and March 2011 respectively.  

Earlier, La Nina played a role of cooling the surface waters in the eastern Pacific Ocean and pushing moisture towards the west. Southern Annular Mode (a climate pattern) coaxed the moisture into interiors of Australia, which caused widespread flooding across the continent. Further more moisture was pushed into the interiors of Australia from the Indian Ocean Dipole that collided with La Niña-borne moisture in the Pacific to increase the moisture content of Australia resulting in one of the wettest periods in the history of the continent.  

The basic region identified in the study for the fall in sea level resulted because maximum rainfall during 2010-11 periods in the vast interiors of Australia called Outback remained inland rather than flowing back to oceans. This happened due to the dry environment of Outback and lack of river runoff. Remaining water got evaporated or sank into the granular dry soil of western plateau and filled Lake Eyre basin in the east.

To measure the difference the researchers used three state-of-the-art instruments for observation, those were:

• NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites: it helped in making detailed measurements of the Earth’s gravitational field and enabled them to monitor changes in the mass of continents.
• To measure the temperature and salinity of the upper 6000 feet of ocean the Argo global array of 3000 free-drifting floats  was used
• To subtract the seasonal variations and estimate the sea level changes globally, satellite-based altimeters were used. These altimeters are calibrated against a network of tide gauges.

Comment: As per the scientists, Australia, the smallest continent of the world has affected the sea level of earth and its effect has been successful in overcoming the recent trend rise in the level of sea due to change in climatic conditions.

The study was authored by John T. Fasullo, Carmen Boening, Felix W. Landerer and R. Steven Nerem. The study was co-authored from Jet Propulsion Laboratory and the University of Colorado at Boulder and was funded by Science Foundation, the sponsor of NCAR, and by NASA.

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