Australia: How Australia's big wet befuddled scientists

So how wet was Australia in 2010 and 2011?

Wet enough, it turns out, to reverse the climb of global sea levels in a temporary shift that baffled scientists.

New research from the US shows the normally dry outback regions of Australia acted like a gigantic sponge, sending sea levels sinking until the water gradually made its way back to the oceans via evaporation or seepage from land.

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Only in Australia could the atmosphere carry such heavy tropical rains to such a large area 

“For an 18-month period beginning in 2010, the oceans mysteriously dropped by about 7 millimetres, more than offsetting the annual rise,” the US National Science Foundation said in a statement before the release of a report to be published next month in the Geophysical Research Letters journal.

Sea levels as measured by satellites over the past 20 years.

“In late 2010, early 2011, there was a whole series of flooding events in Queensland, in Victoria, in the Northern Territory – and then tropical cyclone Yasi hit northern Queensland,” said David Karoly, professor of meteorology at the University of Melbourne. “If you look at the area of Australia and the amount of water that fell, it's not surprising that it had an impact on global sea levels.”

The country had its wettest back-to-back years on record, with rainfall averaging more than 50 per cent above normal, Dr Karoly said.

Sea levels have largely been heading one way for a long time.

The US researchers said Australia's unique topography and the lack of river run-off west of the Great Dividing Range were key to the impact on global sea levels.

"No other continent has this combination of atmospheric set-up and topography," John Fasullo, a lead researcher on the project from the US National Centre for Atmospheric Research, was quoted as saying. "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."

Tropical south

A flash flood in Toowoomba. 2011. Photo: Reuters

That moist air also extended well to the south. On January 13, 2011 weather balloons at Melbourne Airport measured an air column containing the equivalent of 65 millimetres of water.

“That was 20 per cent higher than any previous daily record for the last 50 years,” said Professor Karoly. “It was really indicative that this was tropical air.”

Most of Australia recorded exceptionally wet conditions. Source: BoM

While natural variations were dominant factors in creating the abnormal weather over Australia, carbon emissions related to human activities also played a role. "Global greenhouse (gas) was a contributing factor, making conditions worse than they would have been,” Professor Karoly said.

But the halt to rising sea levels was only temporary.

Those levels have been rising at about 3.2 millimetres a year in recent decades as a warming climate causes water to expand, and also prompts more melting from glaciers and ice sheets.

The 2010-11 years were the wettest two years in a row.

Earlier this week, leaked details of an important United Nations report on climate change indicated that scientists now expect seas will rise between 290 and 820 millimetres by the end of the century, up from a previous forecast range of 180-590 millimetres.

Dr Fasullo said the pause in ocean creep caused by the Australian rainfall events was “a beautiful illustration of how complicated our climate system is”.

John Hunter, an expert at the University of Hobart in sea-level rises associated with climate change, said more such short-term shifts – such as a slowdown in global temperature increases in recent years – could be expected.

“There are always going to be a few surprises along the way,” Dr Hunter said. “It doesn't mean the long-term trend has changed. It just means you have a deviation from it. “

Since 2011, sea-level rises have picked up again, surging at a rate as fast as 10 millimetres a year, the peer-reviewed US report found.