Worsening El Nino

THE world’s most devastating global weather phenomenon – the weather events associated with “El Nino” – will double in frequency to once a decade if global warming remains unchecked.

The last extreme El Nino, in 1997-98, resulted in the hottest year on record, and the accompanying floods, cyclones, droughts and wild fires killed an estimated 23,000 people and caused huge sums in damage, particularly to food production. But, until now, scientists have been unable to agree how climate change will affect the frequency of extreme El Ninos.

The new study, published in the journal Nature Climate Change, concludes that in stark contrast to earlier work, the current rate of carbon emissions would mean twice as many extreme El Ninos over the next 100 years, with profound socio-economic consequences.

“This is a highly unexpected consequence of global warming,” said Prof Mat Collins of the University of Exeter in England, part of the research team. “Previously we had thought that El Nino would be unaffected by climate change. Tropical rainfall conditions such as those experienced in extreme El Ninos have a dramatic influence on the world ... the impact, therefore, on mankind is substantial.”

Another team member, Prof Eric Guilyardi of the University of Reading, said: “This research is the first comprehensive examination of the issue to produce robust and convincing results about extreme El Ninos.”

El Ninos begin with an unusual warming of the sea surface at the tropics of the eastern Pacific and spread to affect many parts of the world. Previous attempts to ascertain the effect of climate change were inconclusive, as different computer climate models produced conflicting results.

By focusing on those models known to best represent the changes in temperature, currents and clouds that occur in the real world, the researchers were able to produce a clear result for the first time. The work showed that climate change is most likely to warm the tropical Pacific waters that drive El Nino more rapidly than surrounding regions, meaning that extreme events would become twice as common.

“This is essentially an ‘irreversible’ climate change phenomenon, and it would take a dramatic reduction in greenhouse emissions over a number of generations to reduce the impact.

“It is even more evidence that cutting emissions would be a good idea,” said Collins.

The most recent extreme El Nino events were in 1982-83 and 1997-98, when warm sea surface temperatures in the normally cool and dry eastern Pacific caused a massive reorganisation of global rainfall.

“Nations in the western Pacific experienced devastating droughts and wildfires, while catastrophic floods occurred in the eastern equatorial region of Ecuador and northern Peru,” said Wenju Cai of the Commonwealth Scientific and Industrial Research Organisation in Victoria, Australia, part of the research team.

In another study, the Climate Council of Australia found that heatwaves in the continent are becoming more frequent, are increasing in intensity and are lasting longer.

It finds that climate change is having a key influence on a trend that has seen the number of hot days in Australia double and the duration and frequency of heatwaves increase in the period between 1971 and 2008.

South-eastern Australia has baked in extreme temperatures in recent weeks, with Melbourne and Adelaide seeing temperatures over 40°C.

The Climate Council is a privately run group of climate scientists and economists who previously formed the government-funded Climate Commission. – Guardian News & Media