Australia - climate change

Australia to see worse drought thanks to intensifying El Niño

New research by the Bureau of Meteorology – published shows El Niño will intensify between 2050 and 2100 thanks to climate change.

Physics,

14 October, 2013

El Niño is a complex interaction between air and sea in the tropical Pacific which controls many of our weather patterns. The findings show that eastern Australia will see worse droughts, while the central and eastern Pacific will see increased rainfall.

During an El Niño – properly known as El Niño-Southern Oscillation or ENSO – parts of the central and eastern Pacific Ocean warm more than usual, while the seas off eastern Australia cool. As warm water produces more moisture, the eastern and central Pacific see increased rainfall, while Australia experiences lower-than-average rainfall or drought.

Australia last saw a weak El Niño event over 2009-2010. The previous strong El Niño was 1997-1998.

El Niño's partner in crime – La Niña – is known for causing opposite effects. The summer of 2010-2011 was one of the strongest La Niña events on record, reflected in rainfall records across eastern Australia, and floods and cyclones in Queensland.

The researchers used four different climate models and found strong agreement between them for decreasing rainfall in eastern Australia.

Currently the Bureau of Meteorology is forecasting neutral El Niño conditions for the remainder of spring and summer.

Dr Scott Power from the Bureau, lead researcher on the paper, told the Australian Science Media Centre that continued global warming has the power to disrupt El Niño and its impacts.

"Until now, there has been great uncertainty about the way in which ENSO [El Niño] might actually change in response to global warming – despite scientists investigating the issue for more than two decades.

"Using the world's latest generation of climate models we discovered a consistent projection for the future of ENSO. Consistency across models increases confidence in the projections they display.

"Projections produced by the models indicate that global warming interferes with the impact that El Niño sea-surface temperature patterns have on rainfall. This interference causes an intensification of El Niño-driven drying in the western Pacific and rainfall increases in the central and eastern equatorial Pacific.

"The future of ENSO and the disruption it causes to the climate of the earth, its people and its ecosystems are clearer now than ever before."

Dr Wenju Chai from CSIRO, who did not contribute to the research, said that the paper is significant in that there is a stronger agreement between different climate models in predicting the future impact of El Niño.

"Up until now, there has been a lack of agreement among computer models as to how ENSO will change in the future."

"During El Niño, Western Pacific countries (Australasia, including Australia) experience unusually low rainfall, while the eastern equatorial Pacific receives more rainfall than usual. This study finds that both the wet and dry anomalies will be greater in future El Niño years. This means that ENSO-induced drought and floods will be more intense in the future."

Explore further: Global warming could change strength of El Nino

El Nino to 'take greater toll'

Australian scientists claim to have provided a clearer answer to a 20-year climate puzzle - but the finding will not be welcome news for farmers, policymakers or the wider public.

SMH,

26 January, 2013

Australian scientists claim to have provided a clearer answer to a 20-year climate puzzle - but the finding will not be welcome news for farmers, policymakers or the wider public.

The El Nino-Southern Oscillation, which operates over the Pacific and is viewed as an engine room for driving variability in the world's atmosphere, has long been studied to understand how it will be affected by global warming from greenhouse gases.

For these sorts of changes, the signal becomes larger as time goes on under the scenarios we've used.

New work by the Centre for Australian Weather and Climate Research, jointly run by the Bureau of Meteorology and CSIRO, shows that the impact of El Nino years - marked by a relative warming of waters in the eastern Pacific and shifting rainfall patterns - will be exacerbated by climate change.

Using the latest climate models, the team found western regions of the Pacific, such as east Australia, will have worse droughts during El Nino years, while the eastern Pacific will experience heavier rains. ''What we found was those two effects are intensified in the future, because global warming interferes with the impact El Nino has,'' Dr Power said, citing peer-reviewed research to be published on Monday in the journal Nature.

Wenju Cai, a senior CSIRO research scientist, said the latest study showed a stronger agreement than earlier climate models.

A satellite view of the equatorial Pacific. Photo: NASA

The results may also show that changes in La Nina years - when western Pacific waters are relatively warm - could bring more extreme conditions to eastern Australia, he said. ''During an El Nino period, the drought in the western Pacific could be more intense, or during La Nina [ones], the floods could be more intense or maybe both,'' Dr Cai said.

While separating the impact of greenhouse gas-induced global warming from natural variability can be difficult, human influence on El Nino patterns becomes clear from the latter part of the 21st century, Dr Power said.

''For these sorts of changes, the signal becomes larger as time goes on under the scenarios we've used,'' he said.

Heat - without the El Nino

Most of the hottest years globally and for Australia have been El Nino-dominant years, such as in 1997-98.

"When the world tends to warm up because of El Nino, so does Australia," Dr Power said. "That's because we tend to get less rainfall, so it dries out and clouds clear, we [then] get more radiation hitting the surface, less evaporation to moderate things, and temperatures go up."

While more research is under way on El Nino periods - such as whether their frequency will change from the current three to eight years - climatologists have been surprised at the unusual heat recorded in Australia over the past year even though El Nino-Southern Oscillation conditions have remained neutral.

"It is sobering to see that we're setting these records in non-El Nino years," Dr Power said.

Record warm sea-surface temperatures and extended periods of heat over central Australia have put the country well on course to record its hottest calendar year.

A record hot summer and winter has also extended into September, which notched the biggest monthly departure ever from long-term averages for heat.

Dr Power, a co-ordinating lead author in the latest Intergovernmental Panel on Climate Change report, said global temperatures are likely to rise 0.3-0.7 degrees over 2016-2035, compared with the past 20-year period.

"The magnitude of the changes [on future El Nino periods] will critically depend on the amount of emissions that the world ultimately ends up producing over coming decades," he said.