Thursday, January 28, 2010

Heatwaves on the rise as record lows decline

ABC News Online, Posted Thu Jan 28, 2010 

New research from the Bureau of Meteorology shows that in the past 50 years, Australia's had far more record high temperatures than low temperatures.

And the scientist who did the research says there are more extremely hot days to come.
The Bureau's Blair Trewin said the trend was increasingly noticeable over the past decade.
"While both high temperature records and low temperature records continue to be set in Australia, we've seen over the last 50 years high records increasingly outnumbered low records," he said.
"And over the last 10-12 years, high temperature records have been broken at a rate two-to-three times higher than low temperature records."
Dr Trewin says while low records are still occurring, they are being set less frequently.
"Low temperature records are still occurring, however, record highs have become increasingly frequent since the mid-1990s," he said.
"In 2009 Australia experienced three major heatwaves - in January/February, August, and November - all of which saw widespread record-breaking over large areas. The last time record lows occurred on that scale was in June 2007 in tropical Australia."
The results were taken from an analysis of 68 locations around Australia covering the period since 1957, and tie in with the warming trend of 0.1-0.2 degrees Celsius per decade over the same period.
The figures also come after Australia experienced its hottest decade since records began in 1910.
"It's consistent with a lot of other information we have. We know there's been consistent warming trend in average temperatures in Australia over that time period," Dr Trewin said.
"We know there's been an increase in the number of days over 35 degrees, a decrease in the number of nights below zero in those places that get as cold as that. So the findings we've made with respect to temperature records are consistent with all of those other pieces of information."
He also said the research had been specifically constructed to avoid any inaccuracy caused by data collection, a claim commonly used by climate-change sceptics to dismiss temperature studies.
"What we did was we took data from 68 locations, spread around Australia," he said.
"We selected locations with the best long-term records over that time and also the most consistent records - data sets - over that time. Because there are some places where, perhaps, the site has moved, or it's been influenced by urban development and you might get misleading results from those."
"And we do things like we look at historical files and see how the local environment around a site has changed.
"So we do take those types of influences into fairly careful account and, in this study, we made sure that we eliminated any locations that we believed were suffering from some of those issues that had been raised about a particular location."
Dr Trewin also said the length of the study helped to minimise the possibility of one reading skewing overall results, such as the 1998 climate data which is cited by many experts as proof the planet is cooling.
"A decade's a very short period of time to be looking at. And in the case of global temperatures, 1998 was a massive El Nino year and if you're only taking trends over 10 years, one outlying year like that can really influence your results," he said.
"But once you go out to 40, 50, 100 years, trends become much less sensitive to the start and end points."
And Dr Trewin is confident the pattern will continue into the future.
"We expect that both with the bringing it up to date just with the last couple of years of information and also into the future, we expect to see average temperatures continue to warm," he said.
"And with that, we would expect to see a continued trend towards more high extremes and fewer cold extremes."

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