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Climate change ‘will double’ El Niño events

By Rachel Banning-Lover (The Telegraph) - January 21, 2014

A critical weather pattern that fuels deadly weather around the world – the El Niño Southern Oscillation (ESNO) – was previously defined as occurring when warm water spreads across the surface of the Pacific and pushes rainfall to the east, causing catastrophic natural disasters.

These extreme meteorological events used to be relatively rare though, only happening once every 20 years, but now Australian climate change experts say one should be expected every decade after re-defining what causes the weather phenomenon.

Until recently, climate experts could not say whether climate change would make El Niños more regular or not as there was no consensus on whether Pacific temperatures will fluctuate more in the future.

The last major El Niño, during 1997 and 1998, killed 23,000 people and caused up to an estimated $45 billion in damage.

It brought flooding to the Americas and Africa, tropical cyclones to Pacific islands, and droughts and wildfires to Australia and south-east Asia.

However, a new study by Wenju Cai and her team at the Commonwealth Scientific and Industrial Research Organization in Melbourne has now re-defined El Niños as a massive re-organisation of rainfall, rather than the result of changes in sea surface temperature.

Using the new definition and looking at usually dry regions in South America experiencing a tenfold increase in rain, they found that climate models do suggest climate change will impact the ESNO weather pattern.

Ms Cai told the New Scientist that “the reason is quite simple”. The eastern Pacific is warming faster than the western Pacific.

As a result, even if surface temperature fluctuations stay the same as today, peak temperatures will still happen more often in the east. Since rainfall follows peak temperature, big disruptions to rainfall will be more common.

Ms Cai’s findings follow other recent research by the Australian Bureau of Meteorology that showed that in future even normal El Niños will have more severe drying and wetting effects.

Dietmar Dommenget, a professor at Monash University in Melbourne, told The New Scientist that these two papers were changing how scientists look at ESNO.

“People have been looking at it in terms of sea surface temperature but maybe that’s not so important. What is really important is the rainfall.”