Extreme El Niño events ‘to double’ with AGW


El Niño

El Niño

A new paper in Nature Climate Change claims that extreme El Niño events are set to double with a warming climate. The ABC reports:

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.”

The fact that the modelling of the El Niño events is based on existing climate models means the conclusions drawn should be treated with a heap of caution. With a single model, garbage in equals garbage out, but with two models, it’s garbage in equals garbage-squared out.

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