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Australia’s Flooding Rains Briefly Slowed Sea Level Rise

Scientists may have zeroed in on the cause of a mysterious 18-month drop in global average sea level that occurred between 2010 and 2011, pointing to events that occurred on the world’s smallest continent: Australia. New research shows that during those two years, flooding rains in Australia, which resulted from a rare combination of factors, took huge quantities of water out of the oceans without returning it, like a library user with mounting late fees.

Flooding in Toowoomba, Australia, in 2011.
Credit: Tim Swinson/flickr.

The study, which is to be published in a forthcoming issue of the journal Geophysical Research Letters, found that peculiarities in Australia’s soils and topography prevented much of the excess rainfall from ever making its way back into the oceans, instead soaking it like a sponge.

As the climate warms, the world’s oceans have steadily risen in recent decades, and the rate of rise has accelerated recently to about 3.2 millimeters per year, or about 1.25 inches per decade. That is because runoff from melting ice sheets and retreating glaciers is making its way into the oceans, and because water expands as it is heated.

However, for an 18-month period starting in 2010 and coinciding with a strong La Niña event in the tropical Pacific Ocean, the oceans dropped by about 7 millimeters, or about 0.3 inches, which caused some climate skeptics to question whether sea level rise had stopped altogether. Since 2011, however, sea level rise has resumed, and at a faster pace than before.

Following a historic drought, Australia was inundated with flooding rains during the 2010-2011 period, with devastating flooding occurring in Queensland, which is in northeastern Australia and contains the city of Brisbane. The study found that the rains resulted from an unusual confluence of three different natural climate cycles, as well as a contribution from global warming-related increases in sea surface temperatures, said coauthor John Fasullo of the National Center for Atmospheric Research, in an interview.

The dip in global average sea level between 2010-2011, based on satellite data.
Credit: NASA JPL.

“We didn’t know how much an effect Australia could have on the global oceans,” Fasullo said, noting that he was surprised to find that the continent “could contain such a large quantity of mass (of water) over a long period of time.”

The researchers used measurements of groundwater storage from NASA’s Gravity Recovery and Climate Experiment satellites, which allowed them to quantify small changes in land mass. They also examined data from an array of sophisticated buoys deployed throughout the Pacific Ocean, and satellite-based altimeters that keep track of global sea level changes.

Fasullo and his co-authors published research last year that tied the observed drop in sea level to the 2010-2011 La Niña, which cooled surface waters in the eastern Pacific while enhancing rainfall in Africa, South America, and Australia. But the researchers were puzzled by the fact that previous La Niñas were not accompanied by such a significant and prolonged dip in sea level, leading them to suspect that other factors were also involved.

The new study shows that it wasn’t just La Niña that caused the sea level rise slowdown, but other cyclical climate phenomena that together produced extraordinary rainfall amounts over the Australian continent. A pattern known as the Southern Annular Mode also helped direct moisture toward Australia, and even more moisture was added by a pattern known as the Indian Ocean Dipole, which is a system of ocean and air circulation throughout the equatorial Indian Ocean that influences rainfall patterns in Australia, among other areas.

Image showing increase in land mass during 2010-2011 in Australia as well as parts of South America.
Credit: NASA JPL.

Fasullo said increased sea surface temperatures in parts of the Pacific Ocean, which are thought to be related to global warming, also boosted the amount of moisture that was directed toward Australia.

Thanks to this combination of factors, Australia endured one of its wettest periods on record, and the lack of river runoff from the continent’s interior meant that most of the rain collected on land and eventually seeped into the ground or evaporated, rather than returning to the ocean.

The rains led to the formation of vast inland seas, Fasullo said, including the Lake Eyre Basin in eastern Australia, which went from “a small lake to a body of water that you couldn’t see across.” The Lake Eyre Basin covers about one-sixth of Australia, and is equivalent in size to the state of Texas. It contains the largest ephemeral lake in the world, which expands dramatically during times of abundant rainfall and ceases to exist in more arid times.

“No other continent has this combination of atmospheric set-up and topography,” Fasullo said in a press release. “Only in Australia could the atmosphere carry such heavy tropical rains to such a large area, only to have those rains fail to make their way to the ocean.”

When viewed over the long-term, the rainfall-related dip in sea level looks more like a small blip amid a steady march toward higher sea levels, which spell serious trouble for coastal cities worldwide.

A forthcoming report from the U.N. Intergovernmental Panel on Climate Change is expected to conclude that the global average sea level may rise by an average of up to 2 feet by 2100, depending on future greenhouse gas emissions and how sensitive the climate system proves to be to those emissions.

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Comments

By Dave (Basking Ridge, NJ 07920)
on August 21st, 2013

To be fair to the many tons of ocean involved, according to GRACE data as reported by NASA/JPL some of that excessive precipitation transfer-from-the-ocean also landed in northern South America and Southeast Asia. And evidently some of that total shared amount has indeed since flowed back into the oceans causing an unusually steep short term rate of rise in global mean sea level (GMSL) since 2011.

BTW: For anyone interested in more details about current GMSL measurements, the current measured background trend for global mean sea level rise is actually better expressed as 3.2+/- 0.4 mm per year. CU: http://sealevel.colorado.edu/content/2013rel5-global-mean-sea-level-time-series-seasonal-signals-removed

AVISO calculate the trend in global mean sea level rise from satellite data slightly differently calling it the reference mean sea level but come up with basically the same number for the same period: 3.19 +/- 0.6mm per year, where the uncertainty range quoted here encompasses a 90% confidence interval.
http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/
This page is also interesting because it provides data showing just how regionally variable mean sea level rise is today.

So for casual conversation purposes the current GMSL rate of rise is somewhere between 1 and 1.5 inches per decade with 90% certainty in Climate Central preferred units.

Reply to this comment

By Atanacio Luna (Quail Valley, CA 92587)
on August 25th, 2013

Related Conjecture: Groundwater approximately equals frozen water on earth. Both have been largely static in earlier human history, thus not affecting GIA (Glacial Isostatic Adjustment) much. Fossil fuels have changed that. 1) provided energy to pump substantial amounts of groundwater. 2) Increased global temperature causing frozen water shifts. and 3) Changed groundwater loads on different parts of continents with changes in precipitation patterns.
A) Will this effect GIA?
B) If so, will it effect plate tectonics?
Pluvinergy’s hypothesizes yes! via over a dozen mechanisms. Example: Place two thick books binder to binder on table. Lift both books where they meet, creating a V shape between them. Place your finger in the V and lower the books, the pressure on your finger forcing the books apart. Magma formation could act as your finger in microscopic or synoptic proportions. We offer resulting in transatlantic rift, and most other plate tectonics.
V and M causation is mostly due to complex wave harmonics, that is: incremental addition of wave motion in a given direction as different effects of gravity waves, per moon and other Astros, GIA, and other planet mechanics.
The result of this conjecture is that fossil fuels may also cause changes in seismic activity, fracking seismic effects being nearly meaningless. 
What do you think? maybe you want to do a paper about it         wink.

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