Extreme El Nino events set to double
Stronger, more often Global warming could double the frequency of catastrophic events linked to extreme El Niños, say scientists.
The findings mean not just a rise in the number of devastating droughts and fires in Australia and Indonesia, and major floods in the normally cold and dry Peru and Ecuador, but also a rise in extreme weather events around the world.
"The influence of extreme El Niños reaches every continent," says Dr Wenju Cai, of CSIRO Marine and Atmospheric Research, who is lead author on a new paper published today in the journal Nature Climate Change.
Cai says the last extreme El Niño in 1997/98 led to 23,000 deaths and $50 billion worth of losses globally.
Under the El Niño weather pattern, the ocean in the eastern Pacific heats up more than normal, bringing more rain to that area and less rain to the western Pacific.
When the warming in the eastern Pacific passes a certain temperature, an extreme El Niño results. This causes extreme droughts in the western Pacific and a 10-fold increase in rain in the eastern equatorial Pacific region.
"Imagine an average of 5 millimetres a day everyday for three months," says Cai.
To investigate how extreme El Niños would respond to a warming planet in the future, Cai and colleagues aggregated 20 different climate models.
Each model covered a 200-year period between 1891 and 2090, and incorporated measurements of CO2 and other factors, both historical and future, as predicted by the IPCC.
The researchers then compared the historical period 1891-1990 with the period 1991-2090 and found an increase in extreme El Niño events.
"The model is simulating an extreme El Niño event 1 per 20 years from 1891-1990 on average," says Cai. "But from 1991 to 2090 the model simulates a doubling of the frequency of extreme El Niño events."
He emphasises it is not possible to identify which specific El Niño event is due to global warming because there will be some that occur anyway.
Cai says in the last two extreme El Niño events led to massive floods and landslides in Peru and Ecuador, resulting in the deaths of many people and seabirds, and coral bleaching.
During extreme El Niños, cyclones also occur in places they do not normally occur, for example in French Polynesia.
The 1982/83 extreme El Niño event caused the infamous Ash Wednesday bushfires in Australia, as well as $10 billion in lost productivity in the Murray Darling Basin, he says.
Cai says scientists believe there was an extreme El Niño event in 1877/78 when, according to a recent US study, 23 million people died globally due to drought-induced famines and floods.
The last El Niño was in 2009/10. This was followed in 2010/11 by a La Niña event, bringing extra flooding rains to Australia.
According to the Bureau of Meteorology it is not clear when the next El Niño is due - such events, which tend to peak in the summer months, can only be predicted 6-9 months out, says Cai.
"It's too early to call," he says.
But, adds Cai, the latest findings suggest when the next El Niño does come it could be an extreme one.
"We are due for a big one because the last extreme El Niño was in 1997/98."