Regional warming occurs in a series of steps rather than as a gradual trend, a new study by Victoria University has found.
Climate scientist Professor Roger Jones from the Centre for Strategic Economic Studies told the Greenhouse 2011 Conference in Cairns this week that south-eastern Australia had experienced two large steps in warming during the past 45 years. The evidence showed most of the change was not due to natural climate variability.
The first step-change was in 1968 when minimum temperature increased by 0.7°C. There was also an underlying change in maximum temperature, which was masked by increased rainfall. During the second period of major change, from 1997-98, maximum temperatures increased by 0.9°C and rainfall fell by 9 per cent.
Most of the warming in south-eastern Australia has occurred during these two periods, with little change in between.
The southern hemisphere also warmed in a step-wise fashion in these two periods. In 1997, the step-change was mirrored globally, with average temperatures worldwide increasing by 0.3°C.
When regional climate simulated by eleven climate models was analysed, the same patterns of change were found. "Early 20th century climate is stable in all simulations until the second half of the 20th century", he said. "Warming begins abruptly in one or two steps, then during the 21st century as greenhouse gas emissions accelerate, regional temperature warms in steps and trends."
The 1968 step-change coincided with major decreases in rainfall over south-west Western Australia. Professor Jones said major effects of the 1997""98 step change in south-eastern Australia included increased fire danger, heat stress, water shortages and faster crop ripening times.
"On the Mornington Peninsula, grapes have ripened at least three weeks faster since an abrupt shift in 1998. The forest fire danger index in Victoria has increased by almost 40 per cent from 1997.
"Most planning for adaptation to climate change is based on assuming gradual change. These findings have the potential to completely alter how we manage changing climate risks."
Professor Jones is available for comment: 0434 543 425
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