Climate change signals raining down but proof will take centuries

For Australia, 2013 looks like being a "year of living extremely" if January is anything to go by.

The Bureau of Meteorology says January was the hottest ever month in just over a century of records.

Nationwide, the January average maximum temperature anomaly was 2.28 degrees, "a substantial increase" on the previous record of 2.17 degrees set in 1932.

And, thanks to the unusual scale of the massive heatwave that dominated the first half of January, all states and territories posted above-average temperatures, the bureau said.

This week's floods, of course, added to the extremes. The Queensland Premier, Campbell Newman, warned damage to the state's economy was $2.4 billion and rising, eclipsing the $2.388 billion bill from the huge flooding of 2011. Insurers don't think it will be that bad for them.

Add in record low rainfall for much of southern Australia, a flurry of bushfires and it looks a lot like climate change is kicking in - or does it?

Professor John McAneney, the director of Risk Frontiers, an independent research group funded mostly by the insurance industry, says that based on a database of natural hazard events in Australia, including some dating back to 1803, "there has been no increase in the frequency of natural hazard events since 1950".

But what of the spiralling insurance claims in the wake of hailstorms, floods, cyclones (think Yasi at $1.4 billion) and bushfires ($4 billion for Victoria's Black Saturday firestorms)?

"What we can see very clearly is that when this dataset … is corrected for the increases in numbers of buildings at risk and their value, no long term trend remains," Professor McAneney said.

''It is indisputable that the rising toll of natural disasters is due to more people and assets at risk."

He said US hurricane modelling to identify a signal climate change is contributing to storm strength suggests it could be a while before the data is definitive. Averaging 18 different climate models, "it's going to take 260 years", he said.

"This whole thing about climate change being responsible for an increase in extreme weather, or natural disasters, is just a fiction really."

Cue howls of protests from climatologists and cries of "gotcha" from climate change doubters? Not quite.

Some climate change signals are clearer than others, and there is no reason to ignore the direction most indicators are clearly pointed, said Andrew Ash, director of the climate adaptation flagship at the CSIRO.

"It doesn't mean all extremes are changing," Mr Ash said.

Take temperature, for instance. The weather bureau notes that during 2001-11, the frequency of record high temperatures in Australia was 2.8 times (for maximum temperatures) and 5.2 times for minimums than the rate of record low temperatures.

Sea temperatures are also increasing, with waters in the Australian region about 0.6-0.7 degrees warmer than they were in 1900, said Neil Plummer, assistant director of the weather bureau's climate information services.

Add a warmer atmosphere - with temperatures about 1 degree higher than pre-industrial levels and rising - there is little doubt more moisture can be held and then dumped in the form of more severe rain deluges.

A peer-reviewed report for the American Meteorological Society's Journal of Climate by researchers including Seth Westra, a hydrologist at the University of Adelaide, bears that out. The report found statistically significant increasing trends globally of annual maximum daily precipitation, using a dataset of 8326 high quality observing sites with more than 30 years of records.

The median intensity of extreme precipitation increases "in proportion with changes in global mean temperature at a rate of between 5.9 per cent and 7.7 per cent per degree, depending on the method of analysis," the report found.

The big wet, when it comes, is getting wetter. But what of Australia? The weather bureau says it depends where you look.

The annual number of days with more than 30 millimetres of rain from 1950-2012 has decreased in the southern and eastern parts of the country but increased in the north.

And as for the frequency of disasters, such as cyclones, the answer is complex because there aren't many instances in the record to count.

"Because you're dealing with a very small number of very extreme events … the size of the signal you would need to have before it was statistically significant is detectable is quite big," said Blair Trewin, a senior climatologist at the bureau.

"The absence of evidence is not the evidence of absence."

Smartphone
Tablet - Narrow
Tablet - Wide
Desktop