Antinuclear

Until recently, public health authorities would issue a warning whenever the temperature was likely to exceed a certain level.

However, heatwaves are also related to the conditions people are accustomed to. To reflect that, the Bureau of Meteorology last year pioneered a heatwave service that predicts the severity of coming heatwaves based on both how far temperatures are likely to deviate from historical averages but also taking into account the previous month’s weather.

In a further tweak, the bureau has added charts to assess the impact of each heatwave after it’s hit. That’s needed because people often don’t realise the damage to health can come from exposure to prolonged warmth rather than a particular temperature spike.

“If the body doesn’t have time to recover overnight, or for some period during 24 hours, that’s when significant problems start to emerge,” said Alasdair Hainsworth, assistant director of hazard prediction services at the bureau.

“We know that Australia is warming … and we believe we should provide some level of warning associated with that,” Mr Hainsworth said, adding the charts may one day be common features of weather reports.

Indeed, of the emerging signals of climate change in Australia, rising temperatures and increasing heatwaves are the probably the clearest.

For New South Wales, average maximum temperatures have already risen by half a degree over the last two decades or so. They are likely to increase by another 0.7 degrees by 2030 and as much as 2.6 degrees by 2070, according to research released by the state government and the University of NSW earlier this month.

“We know heatwaves have a big impact,” said Matthew Riley, director of climate and atmospheric science for the Office of Environment and Heritage. “They are the costliest natural disaster in terms of the loss of human life in Australia.”

While Victoria’s 2009 Black Saturday bushfires killed 174 people, at least 370 people died during the heatwave that preceded the fires – drawing much less public or media focus.

NSW Health has identified people aged over 75, infants and those taking perscription medicine that restricts perspiration as among those most at risk from heat stress.

Human physiology means that excess warmth starts to undermine health for most of us when body temperatures exceed 37.8 degrees. Similar damage is inflicted on plants when certain thresholds are crossed (see related article).

When overlaid on Australia’s famously variable climate, the existing temperature rise is also associated with heatwaves becoming more intense, more common, lasting longer, and starting earlier in spring.

Research published in August in the Journal of Climate predicts Sydney will experience as many as 42 heatwave days each summer by the end of the century, assuming greenhouse gas emissions remain at the high end of trajectories. That tally would exceed even Perth’s 40 such days and Melbourne’s 12.

“Definitely we’ll see more heatwaves and the number of heatwave days will increase,” said Sarah Perkins, a heatwave expert at UNSW’s ARC Centre of Excellence for Climate System Science and one of the report’s authors. “It’s not a good story.”

By contrast, Sydney had just three heatwave days on average 60 years ago and about six to seven now, Dr Perkins said. A heatwave is defined as having at least three days in a row with temperatures in the top 10 per cent for those days.

The government-backed study, meanwhile, generated scenarios down to 10km resolution for the first time, giving local governments greater clarity on what to expect as the climate shifts……….http://www.smh.com.au/environment/climate-change/as-shepherds-watched-it-got-hotter-and-hotter-20141223-124o27.html