Australian heatwaves getting hotter and longer, says Climate Council

Council releases 1971-2008 climate findings as Adelaide and Melbourne brace for historic heat  

Oliver Milman, 

theguardian.com, Thursday 16 January 2014

ßee also - Australian heatwaves more frequent,  hotter and longer, ABC News Online, 16 January 2014

Heatwaves in Australia are becoming more frequent, are increasing in intensity and are lasting longer, according to an interim report by the Climate Council.

The report, which will be released in full in February, 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 this week, with Melbourne set for four consecutive days over 40C – a run not replicated since 1908. Adelaide is due to go one further and have five days over 40C, with Thursday's forecast of 46C threatening to break city's record temperature of 46.1C.

The Climate Council, a privately run group of climate scientists and economists who previously formed the government-funded Climate Commission, defines a heatwave to be at least three consecutive days at a temperature in the top 10% for that time of year.

Its interim report states there will still be record cold events but that these events are being eclipsed by record hot events by a ratio of three to one. Heatwave frequency in Australia will "increase significantly" in the future, the report warns.

"As greenhouse gases continue to accumulate in the atmosphere from the burning of fossil fuels, more heat is trapped in the lower atmosphere," the report states. "This increases the likelihood that hot weather will occur and that heatwaves will become longer and more intense.

"It is crucial that communities, emergency services, health and medical services and other authorities prepare for the increases that are already occurring in the severity and frequency of many types of extreme weather.

"The south-east of Australia, including many of our largest population centres, stands out as being at increased risk from many extreme weather events – including heatwaves."

Dr Sarah Perkins, report co-author and research fellow at the UNSW, told Guardian Australia that the current heatwave was happening during a "neutral" period of climatic variability.

Before the 2009 Black Saturday fires, there was a decade-long drought, which produced some climatic variability reasons behind it," she said.

"This year, we aren't in an El Niño, we're in a neutral pattern, so we might expect some extreme weather but not this hot scorching weather. Last year was a neutral year too, on the back of a strong La Niña, and we still got extreme weather.

"I'm not discounting natural variability, but there is still the background signal of climate change. The high-pressure system probably would've happened anyway, but climate change is exacerbating these events.

"While we can't blame climate change for any one event, we can certainly see its fingerprint. This is another link in the chain."

Perkins said her latest work had analysed heatwave trends up to 2013. She said the trend "just gets worse – it's a bit scary really".

"We are experiencing between one to three extra heatwave days a year, compared to the long term average, which doesn't sound a lot but it doesn't need many of these days to kill people or cause damage," she said.

"And this is with background warming of 1C. If current trends continue and we get to 4C warming, it will be a whole lot worse than now."

Perkins' fellow report author Will Steffen said the increase in heatwaves would have a wide range of impacts on the way Australians live.

"Heatwaves have significant impacts on our health, our infrastructure, our agriculture and our ecosystems," he said.

"It is essential that we understand the influence of climate change on heatwaves to ensure that health services, transport providers, farmers and the community are prepared for what is happening now and what will happen increasingly in the future.

"Australia has always had hot weather. However, climate change is loading the dice toward more extreme hot weather."

The Greens have cited the heatwave in an attack on Tony Abbott's climate change policies, calling for him to abandon plans to dismantle the carbon pricing system.

"The Climate Council has warned that global warming will bring more extreme weather and heatwaves and we can't pretend it's not going to happen," said the Greens senator Lee Rhiannon. "We must prepare for it and stop it getting worse by reducing greenhouse pollution.

"The clean energy laws are already reducing greenhouse pollution and creating jobs. It really is time for Tony Abbott to abandon his ideological rejection of the climate science and put the Australian community first."

The Department of Environment has been contacted for its response to the report.

Old-growth forests seen more valuable as carbon sinks: study

The Age, January 16, 2014

Bigger trees grow faster than smaller ones, contradicting previous assumptions that growth rates slowed with age, according to a study in the journal Nature. That means larger trees will absorb carbon dioxide faster.

Growth rates increased with size in 97 per cent of tropical and temperate trees, according to a study published today of more than 650,000 individual trees from 403 species. As part of photosynthesis, trees absorb greenhouse gases that cause global warming.

The results may change the way researchers create climate models, said Nate Stephenson, a forest ecologist with the U.S. Geological Survey in Three Rivers, California. Under the United Nations clean development mechanism, large-scale tree planting projects in developing countries may apply for emissions credits that can be traded and sold.

"This finding is going to be surprising to a lot of people," said Stephenson, who co-wrote the study. "Let's say you're the manager of a sports team -- what we found is the equivalent of your star players are a bunch of 90-year-olds. In human terms, we expect our star players to be in their 20s, 30s, maybe in their 40s, but not in their 90s."

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Less mature forests still play an important role in sucking carbon from the atmosphere, he said, in part because there are more younger trees than older ones.

"In these old forests, which already hold a huge amount of carbon in them, it turns out that the star players are the biggest trees in old forests," Stephenson said yesterday in a telephone interview. "If you're trying to look at the role of forests in the future and feedbacks to climatic changes, you've got to get the players right."

Climate change set to give us a home without the gumtrees

Lucy Cormack

The Age, January 13, 2014 

Australia's standing as the home among the gumtrees could be challenged, with increased climate stress causing extensive change to Australia's eucalypt ecosystems.

A study by the National Environmental Research Program's Environmental Decisions Hub has found that climate stress on eucalypts will mean many of Australia's 750 species will struggle to cope with climate change.

''Those that will be most affected are the Eucalyptus and Corymbia species in the central desert and open woodlands area,'' said author Nathalie Butt of the NERP Environmental Decisions Hub and the University of Queensland.

The study found that ''under the mid-range climate scenario, these species will lose 20 per cent of their climate space, and twice that under the extreme scenario''.

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The mid-range scenario suggests that ''temperatures will increase by more than 1C by 2055 and by more than 2C by 2085. For the extreme scenario temperatures will increase by more than 1.5C and 2.5C respectively'', Dr Butt said. She said there is additional concern for the impact these conditions will have on wildlife in such areas. ''Trees are habitats and food sources. So this will have a cascade effect on birds, bats and invertebrates that are reliant on eucalypt, and it will affect pollinators as well,'' she said.

While carbon dioxide alone may contribute to additional plant growth, rising heat extremes and rainfall shortages could counter any gains. ''No matter how much carbon dioxide there is, there will become a point where water limitation will override that. What the climate projections are suggesting is that the seasonality of rainfall will increase so there will be longer dry seasons,'' Dr Butt said.

One expected change is the shift of open woodland areas to savannah-like conditions, with more grassland.

As eucalypt ecosystems adjust to cope with warmer and drier conditions it is predicted that trees may shift their ranges towards the coast where growing conditions are more favourable, Dr Butt said.

Australia’s hottest year was no freak event: humans caused it

The Conversation, 6 January 2014

Sophie Lewis, Postdoctoral Research Fellow at University of Melbourne,  

David Karoly, Professor of Atmospheric Science at University of Melbourne

See also  - BoM, Annual climate statement 2013,

 - The Guardian, Australia's hottest year recorded in 2013,

 - The Age, 2013 confirmed as Australia's hottest year on record,

 - ABC News, 2013 was hottest year on record in Australia

The Bureau of Meteorology has confirmed that 2013 was the hottest year in Australia since records began in 1910.

Unusual heat was a persistent feature throughout the year. For the continent as a whole, we experienced our hottest day on record on January 7. Then January was the hottest month on record, and the 2012-13 summer was the hottest recorded for the nation.

The nation-wide temperature record set for the month of September exceeded the previous record by more than a degree. This was the largest temperature anomaly for any month yet recorded.

Averaged across all of Australia, the temperature for 2013 was 1.2C above the 1961-1990 average, and well above the previous record hot year of 2005 of 1.03C above average.

What caused these extreme temperatures? Climate scientists have a problem: because climate deals with averages and trends, we can't attribute specific records to a particular cause.

But our research has made significant headway in identifying the causes of climate events, by calculating how much various factors increase the risk of extreme climate events occurring. And we have found sobering results.

We previously analysed the role human-caused climate change played in recent extremes across Australia.

For various record-breaking 2013 Australian temperatures, we investigated the contributing factors to temperature extremes using a suite of state-of-the-art global climate models. The models simulated well the natural variability of Australian temperatures.

Using this approach, we calculated the probability of hot Australian temperatures in model experiments. These incorporated human (changes in greenhouse gases, aerosols and ozone) and natural (solar radiation changes and volcanic) factors. We compared these probabilities to those calculated for a parallel set of experiments that include only natural factors. In this way, natural and human climate influences can be separated.

In our previous studies, we then applied an approach (known as Fraction of Attributable Risk) widely used in health and population studies to quantify the contribution of a risk factor to the occurrence of a disease. Health studies, for example, can quantify how much smoking increases the risk of lung cancer.

Using the climate models, the Fraction of Attributable Risk (FAR) shows how much the risk of extreme temperatures increases thanks to human influences.

In our earlier study of our record hot Australian summer of 2012-13, we found that it was very likely (with 90% confidence) that human influences increased the odds of extreme summers such as 2012-13 by at least five times.

In August 2013, Australia broke the record for the hottest 12-month period. The odds of this occurring increased again from the hottest summer. We found that human influence increased the odds of setting this new record by at least 100 times.

Recent extreme temperatures are exceeding previous records by increasingly large margins. The chance of reaching these extreme temperatures from natural climate variations alone is becoming increasingly unlikely. When we considered the 12-month record at the end of August, it was nearly impossible for this temperature extreme to occur from natural climate variations alone in these model experiments.

We have just completed a preliminary investigation of contributing factors for the record Australian temperature in the 2013 calendar year.

In the model experiments, it is impossible to reach such a temperature record due to natural climate variations alone. In climate model simulations with only natural factors, none of the nearly 13,000 model years analysed exceed the previous hottest year recorded back in 2005.

In contrast, in model simulations including both natural and human factors, such as increasing greenhouse gases, record temperatures occur approximately once in every ten years during the period 2006 to 2020. (On a mathematical note, as there is no instance in which the record hot yearly temperature occurred without human contributions, the FAR value is one.)

Clearly both natural climate variability and global warming from humans contribute to recent temperature records. Natural variability always plays a major role in the occurrence of weather and climate extremes. But in the case of our recent hottest year on record, human-caused global warming made a crucial contribution to our extreme temperatures.

Our extensive catalogue of 2013 record-breaking events in Australia occurred in a global context of increasing temperatures that must be considered. Globally, 2013 will likely rank as the 6^th hottest year recorded.

So to return to our question, what caused the 2013 record hot year across Australia? Simply put, our climate has changed due to human activities. Recent extremes, such as this hot year, are occurring well outside the bounds of natural climate variations alone.