Greenhouse gases made hottest year on record '2,000 times more likely'

Australia’s hottest year on record in 2013 would’ve been “virtually impossible” without human-driven climate change, with the record temperatures made 2,000 times more likely due to greenhouse gases, research has found.

Four separate research papers into last year’s record heat have identified a distinctive human “fingerprint” on the series of highs, which included Australia’s hottest day, month, summer and spring since records began in 1910.

Researchers ran a number of simulations that looked at how 2013 would have unfolded without the influence of warming gases, such as those derived from burning fossil fuels.

Overall, the additional greenhouses doubled the chance of the most intense heatwaves, made extreme summers five times more likely and increased by seven-fold the chance of hot, dry drought-like conditions.

Specifically, the record heat of 2013 was “virtually impossible” without the influence of global warming, with greenhouse gases making the unprecedented temperatures 2,000 times more likely.

“When it comes to what helped cause our hottest year on record, climate change is no longer a prime suspect, it is the guilty party,” said Prof David Karoly of the University of Melbourne, who contributed to the research.

“Too often we talk about climate change impacts as if they are far in the future. This research shows they are here, now.”

Researchers from the University of NSW, University of Melbourne and the Australian National University (ANU) worked on the project for a special edition of the Bulletin of the American Meteorological Society.

While natural variability regularly causes hot years, the researchers insist that the level of heat experienced in 2013 suggests that greenhouse gases were a critical influence.

Dr Sarah Perkins, research fellow at UNSW, said the research was similar to the way that epidemiologists calculate the contribution of smoking towards lung cancer.

“I’d say there is a greater than 90% certainty that human-induced climate change increased the likelihood of that number and intensity of heatwaves,” she said.

“I’m a bit concerned by that because that summer of 2012 and 2013 was a neutral summer, we should’ve had average conditions with a few warm days. What happens when we have an intense El Nino?”

El Nino is a periodic climatic phenomenon that causes the warming of portion of the Pacific, causing unusually warm weather across Australia.

“The records were absolutely blitzed last year in a way we’ve never seen before,” Perkins said. “We need to reduce greenhouse gases and quickly, but I’m not sure how likely that is.

“We certainly need to make sure hospitals are prepared, give out warnings about heatwaves and provide good public education such as the importance to drink lots of water.”

Dr Sophie Lewis, researcher at ANU, said while not every year will be warmer than the last, it’s likely Australia will see increasingly hot summers in the future.

“We saw unusual heat throughout 2013, it was quite remarkable,” she said. “There was quite a dramatic contribution from greenhouse gases.”

2013’s average temperature was 1.2C above the long-term average, according to the Bureau of Meteorology.

Last January’s heatwave set records for the hottest day, week and month on record, as well as a new record for the number of consecutive days the national average temperature exceeded 39C – seven days between 2 and 8 January.

Australia has warmed by nearly 1C over the past century. The BoM and CSIRO have estimated that Australia could warm by as much as 5C by 2070, if current high emissions levels aren’t dramatically slashed.

Even if the planet keeps to an internationally-agreed goal of limiting warming to below 2C, Australia is likely to experience significant changes to rainfall patterns, extreme heatwave and drought frequency by the end of the century, especially in the southeast of the country.