Climate change a key factor in extreme weather, experts say

Date

March 4, 2013

A few years ago, talking about weather and climate change in the same breath was a cardinal sin for scientists.

Now it has become impossible to have a conversation about the weather without discussing wider climate trends, according to researchers who prepared the Australian Climate Commission’s latest report.

The report, The Angry Summer, says behind the litany of broken heat and rainfall records this year, a clear pattern has now emerged.

”Statistically, there is a one in 500 chance that we are talking about natural variation causing all these new records,” said Will Steffen, the report’s lead author and director of the Australian National University’s Climate Change Institute. ”Not too many people would want to put their life savings on a 500-1 horse.”

”We are talking about a massive amount of additional energy, most of which is being held around the surface layers of the ocean, which is driving the increased evaporation and rainfall,” Professor Steffen said.

The tumbling of records had prompted conversations in the scientific community to turn a corner, he said. Previously, ”weather is not climate” was the mantra, but now the additional boost from greenhouse gases was influencing every event.

It might even be the case that the mantra chanted after every catastrophic weather event – that it can’t be said to be caused by climate change, but it shows what climate change will do – has become a thing of the past.

”I think the steroids analogy is a useful one,” Professor Steffen said. ”Steroids do not create elite athletes – they are already very good athletes. What happens when athletes start taking steroids is that suddenly the same athletes are breaking more records, more often. We are seeing a similar process with the Earth’s climate.”

The past summer has been the hottest in Australian records. In the 102 years of uniform national weather records, there have been 21 days when the entire continent averaged more than 39 degrees – and eight of those took place this year.

Rainfall extremes have also smashed records, particularly along the east coast, with more rain contributing to floods and less to watering crops. The effects have also continued into autumn, with parts of Sydney experiencing a month’s average rainfall in the past three days.

The intensity of the weather was considered highly unusual because it took place in a year without an El Nino cycle – a periodic phase of warm, dry conditions that pushes up temperatures. The previous three hottest summers recorded in Australia all took place in El Nino years.

Australia does not exist in a bubble and extremes here have been mirrored around the world. The US also had the hottest summer on record in 2012.

”In summary, there is now an ongoing fundamental shift in the climate system,” the commission’s report said.

”It is highly likely that extreme hot weather will become even more frequent and severe in Australia and around the globe over the coming decades.

”The decisions we make this decade will largely determine the severity of climate change and its influence on extreme events for our grandchildren.”

The report has been reviewed for accuracy by scientists from leading universities, the Bureau of Meteorology and the CSIRO, and endorsed by a range of emergency services and health groups, including the Australian Medical Association.