Sunday, October 13, 2013

Bushfire risks will get worse, research shows

Peter Hannam, Carbon economy editor  
The Age, October 14, 2013

Scientists claim to have provided a clearer answer to a 20-year climate puzzle, but the finding won't 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 as humans emit more greenhouse gases.

New work by the Centre for Australian Weather and Climate Research, jointly run by the Bureau of Meteorology and CSIRO, shows 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.

''There's an intensification of changes in rainfall that are driven by El Nino,'' said Scott Power, research leader and a senior climate scientist at the bureau.

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

Prolonged or aggravated droughts are bad for farmers and also contribute to more dangerous bushfire seasons because fuel dryness is a big factor in elevated risk.

Wenju Cai, a senior CSIRO research scientist, said the latest research was significant as it showed a stronger agreement than in earlier climate models. The results may also show changes in La Nina years - when western Pacific waters are relatively warm - could also 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.

Dr Power says while separating the impact from greenhouse gas-induced global warming from natural variability can be difficult, modelling shows humans' influence on ENSO patterns becomes clear from the latter part of this century. ''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 Ninos - 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 ENSO 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 recently released 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 Ninos) will critically depend on the amount of emissions that the world ultimately ends up producing over coming decades," he said.

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