Sydney and Melbourne can expect summer days when the mercury climbs to 50 degrees within a couple of decades if greenhouse gas emissions continue to rise, new research has found.
The study, led by Sophie Lewis at the Australian National University, analysed new models being prepared for the Intergovernmental Panel on Climate Change (IPCC) to examine the difference between a 1.5- and 2-degree warming limit compared with pre-industrial times.
For Sydney and Melbourne, populations could swelter in 50-degree weather even if the 2-degree global warming limit agreed in the 2015 Paris accord were achieved, according to the research co-authored by Andrew King from Melbourne University and published Wednesday in Geophysical Research Letters.
The current records for the two cities are 45.8 degrees for Sydney, set on January 18, 2013, and 46.4 degrees for Melbourne on Black Saturday, 7 February, 2009. Such hot days increase the risks of bushfires.
What seems like a small increase in average temperatures, say 1 degree, can lead to a two- or three-fold acceleration in the severity of the extremes. Temperature records are being broken frequently in Australia, with hot records 12 times more likely to be set than cold ones since 2000. Under a high carbon emissions scenario, 50-degree days could arrive “as early as the 2040.
Even with less variability than land, oceans are also seeing significant warming. For temperature-sensitive coral reefs, the past few years of ocean heatwaves has triggered mass bleaching including on the Great Barrier Reef.