Melbourne’s climate can be expected to warm across all seasons, with less rainfall in winter and spring but more intense rain events, according to the latest projections by the CSIRO and the Bureau of Meteorology.
The first update of the agencies’ Natural Resource Management report since 2007 builds on improved modelling to project how the climate for the city and the country is likely to differ by 2030 and 2090.
Since 2001, extreme heat records have exceeded cold records throughout Australia by three to one for maximum temperatures and five to one for minimums. Heatwaves have increased in duration, frequency and intensity in many parts of the country, the report says.
“We expect more hot days and hotter hot days and fewer cold days,” CSIRO climate unit group leader Kevin Hennessy said.
“We’re starting to see what we can expect in the future with greater frequency and intensity.”
Australia’s average temperatures have already warmed 0.9 degrees since 1910, with rising greenhouse gases a contributing factor. Further warming and other climate impacts are already locked in for 2030, but the severity and extent of changes beyond then hinge on whether global carbon emissions are reduced.
“Beyond 2030, the different types of emission scenarios really matter and global action to reduce emissions can have a big effect on the ultimate impacts,” Mr Hennessy said.
The wide-ranging report from the CSIRO and weather bureau comes as governments around the world, including Australia’s, are readying pledges to cut greenhouse gas emissions after 2020. The United Nations wants the promises to be made public by the end of March to add momentum towards a summit in Paris in December to set a new global climate treaty.
Major climate agencies in the United States and Japan have declared 2014 to be the world’s hottest year on record, eclipsing 2005 and 2010. For Australia, 2013 was its hottest, with 2014 ranked third.
The latest report includes projections for Australia’s sea-level rises, a shorter ski season with shallower snow depths, and a longer, more intense fire season. The models have “medium confidence” that tropical cyclones would be fewer but more intense when they made landfall.
The report is particularly aimed at getting planners to prepare for damage from a more volatile climate.
“There really needs to be a greater consciousness of the need to build resilience to these extreme weather events,” Mr Hennessy said.
“It’s the extreme weather events that are really going to have the biggest impacts.”
A separate study, released on Monday by Nature Climate Change, by CSIRO’s Cai Wenju and other researchers, found that the number of extreme La Nina events will almost double under current carbon emissions trajectories from one in 23 years during the 20thcentury to one in 13 years in the 21st. Ominously, about 75 per cent of the increase would come with super La Nina events following hard on the heels of their counterparts – extreme El Nino years.
For Melbourne, average temperatures will increase across all seasons, the CSIRO/Bureau of Meteorology report found. By 2030, summer temperatures, for instance, are likely to be 0.6 degrees warmer than the average for 1986-2005, and depending on the emissions scenario, 1.5-3.4 degrees warmer by 2090.
How rainfall patterns change is less clearcut in a warming world. Southern Australia – particularly the far south-west and the far south-east – is likely to have drier winters, forcing farmers to alter crops and stock to adjust.
For Melbourne, rainfall may drop about 2 per cent throughout the year by 2030 and 7 to 9 per cent by 2090. For the latter year, the drop in winter rainfall may be as much as 10 per cent in winter and 19 per cent in spring.
While summer rains may increase for much of the country, rising temperatures are likely to cause more evaporation. Overall soil moisture and run-off levels are also likely to drop, affecting agriculture and water management, the report found.
