“If we continue with business-as-usual emissions, extreme seasons will inevitably be the norm within decades,” said Lewis. “If we don’t reduce our rate of emissions the record hot summer of 2013 in Australia – when we saw temperatures approaching 50 degrees Celsius in some areas – could be just another average summer season by 2035,” she added.

“This research tells us we can potentially prevent record-breaking seasonal temperatures from becoming average at a regional level,” said Lewis. The idea of a new normal has been used repeatedly when talking about climate change but had never been clearly defined until researchers developed a scientific definition for the term.

“Based on a specific starting point, we determined a new normal occurred when at least half of the years following an extreme year were cooler and half warmer. Only then can a new normal state be declared,” Lewis said. This process was also used to determine new normal conditions for seasonal and regional changes to the climate, she said.

Using the ANU’s National Computational Infrastructure supercomputer to run climate models, the researchers explored when new normal states would appear under the Intergovernmental Panel for Climate Change’s (IPCC) four emissions pathways. The research team examined seasonal temperatures from December to February across Australia, Europe, Asia and North America.

“The results revealed that while global average temperatures would inevitably enter a new normal under all emissions scenarios, this was not the case at seasonal and regional levels,” said Lewis. “We found that with prompt action to reduce greenhouse gases a new normal might never occur in the 21st century at regional levels during the Southern Hemisphere summer and Northern Hemisphere winter,” she said. The research was published in the Bulletin of the American Meterological Society.