Global warming likely to 'energise' El Nino effect, research shows

Peter Hannam, Carbon economy editor   

The Age, October 31, 2013  

Australia may face more intense and frequent bouts of extreme weather in the future as global warming "energises" the El Nino-Southern Oscillation (ENSO), the dominant climate system over the Pacific, according to an Australian-led team of researchers.

The research, led by Shayne McGregor at the University of NSW's Climate Change Research Centre, found that the ENSO phenomena were more active and intense during the 1979-2009 period that at any time in the past 600 years.

"Our research suggests in a warming world we are likely to see more extreme El Nino and La Nina events, which over the past decade in Australia have been related to extreme flooding, persistent droughts and dangerous fire seasons," said Dr McGregor.

An El Nino occurs when the central and eastern Pacific waters are relatively warm, weakening easterly trade winds. A reduction in clouds typically results in droughts and heatwaves for eastern Australia in particular, such as during 1982-83 and 1997-98.

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La Nina years see the patterns reverse, with sea-surface temperatures to Australia's north relatively warm, with floods more common.

"In Australia we don't want El Nino to become more variable," said Matthew England, a co-author of the report published in the Climate of the Past journal, and also from the Climate Change Research Centre. "We're possibly having slightly more events, and they're becoming more intense when they do occur."

Professor England said the research – "Inferred changes in El Nino-South Oscillation variance over the past six centuries" – found a minimum of ENSO variance during the so-called Little Ice Age from 1550-1880 when parts of Europe were "incredibly cold".

The opposite looks likely to be true, however, as humans pump more greenhouse gases into the atmosphere, driving temperatures higher.

"If we warm the planet we tend to energise El Nino," Professor England said. "We tend to excite it to become more variable, and so the events become stronger."

Karl Braganza, manager of climate monitoring at the Bureau of Meteorology, said research is ongoing to examine the link between climate change and extreme weather.

"If they can show a relationship with global temperatures [and ENSO variance], that's a pretty important result," Dr Braganza said of the latest research. (A separate study out earlier this month found that ENSO systems could have a greater impact on Australia in the future even if they did not intensify.)

Australia's extraordinary run of above-average temperatures continued in October despite ENSO being a "neutral" mode, neither El Nino or La Nina.

Sydney, for instance, recorded its second-hottest October on record by daytime and equalled the highest number of days of 32 degrees or warmer weather at five. Brisbane had its hottest October with an average maximum of 28.8 degrees.

Nationally, this month will probably be among the 10 warmest Octobers over the past century, the bureau said. That's enough to make both the past 12 months and the year-to-date periods, the hottest on record for Australia.

"A lot of climate experts are expecting the global climate to take a step up the next time an El Nino occurs," Professor England said. "Temperatures that year will break records in a significant way."

Bushfire risks will get worse, research shows

Peter Hannam, Carbon economy editor  

The Age, October 14, 2013

See Nature Online - Robust twenty-first-century projections of El Niño and related precipitation variability, Power et al.

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.

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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.

New climates for Melbourne, Sydney predicted

Nicky Phillips, Science Reporter  

The Age, October 9, 2013

See Nature 502,  183–187 (10 October 2013), Mori et al., The projected timing of climate departure from recent variability

See also The Guardian, 10 October, John Abraham, Global warming – a world of extremes and biological hotspots

And ABC Online, 10 October, Stephanie Small, Researchers warn record temperatures could hit as early as 2020

Melbourne has just endured its hottest September on record. Sydney is predicted to set an October temperature record on Thursday.

But when do we stop talking about breaking records and admit we've got a radically different climate?

In Melbourne, a new study suggests, it will be 2045. In Sydney that time will come in 2038.

Climate scientists have created an index of the year when the average climate of any given region on earth will likely push outside the extreme records experienced in the past 150 years should greenhouse gas emissions continue unabated.

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This means that regardless of the natural variation in the climate, the lowest monthly dips in temperature will still be hotter than the planet has experienced in the past century and a half.

And the heatwaves many countries have endured in recent years will be part of the new normal.

Research leader Camilo Mora, from the University of Hawaii, said while scientists had repeatedly warned about climate change and its likely effects on biodiversity and people, their study showed change was already upon us. "Within my generation, whatever climate we were used to will be a thing of the past," said Dr Mora.

The index, published in the journal Nature, found if emissions continued under a business as usual scenario, countries in the tropics would be the first to enter new climate territory, around 2038.

Parts of Indonesia would face such conditions by the end of the decade, while the average global temperature would depart from the climate variability of the last 150 years by 2047.

If emissions were stabilised in the coming decades the shift could be delayed until 2069.

The index projections, created from 39 global climate models from 12 countries, used the minimum and maximum temperatures between 1850 and 2005 to define the boundaries of historical variations in climate at any given location.

From climate projections of the next 100 years they calculated the year in which the average climate for a given location would shift outside the extremes of the past 150 years.

The shifts will have far-reaching effects on the environment and people, particularly food and water supply, the spread of infectious diseases and increase the incidence of heat stress, said the researchers.

Study co-author Ryan Longman said many of the first countries to be impacted had the least capacity to respond, but were, ironically, the countries least responsible for climate change in the first place.

Australian climate scientist Sarah Perkins, from the ARC Centre of Excellence for Climate System Science, said the study's results were in line with the latest global projections.

But she expressed reservations about the study's time frames, saying climate models were not designed to provide projections for such precise times and locations such as a year or a city.