CSIRO: warming up to five degrees by 2070

Even an La Niña event and cool weather in Australia in 2010 and 2011 haven’t reversed the overall long-term trend to a warmer globe, according to Australia’s latest State of the Climate report.

The report was assembled by Australia’s peak science body, the Commonwealth Scientific and Industrial Research Organisation, and the Bureau of Meteorology. It predicts ongoing global temperature increases, with Australia likely to experience between 1°C and 5°C increases by 2070.

The La Niña event – which has soaked the country for two successive summers and brought flooding in Queensland, New South Wales and Victoria – damped the trend for 2010 and 2011. Temperatures in those two years in Australia were kept below the long-term average by 0.24°C, the report states, however 2010 was the warmest on record during a La Niña event and still managed to be the 11th warmest year, the report says.

“The highest temperatures on record are occurring with greater frequency and over greater areas of Australia”, the Bureau of Meteorology’s Dr Karl Braganza told ABC Radio.

That view is supported by CSIRO CEO Dr Megan Clark said: “We’ve seen changes in CO₂ over very long geological history, but never this fast.”

Other key points in the report are: global CO₂ emissions from 2009 to 2010 grew by 5.9 percent (reversing a small decline in the global financial crisis years of 2008-2009); sea surface temperatures globally are rising, and the rise is faster around Australia; and this country’s sea level rise since 1993 is at least equal to, and often greater than, the global average.

The global temperature increase, the report states, “continues the trend since the 1950s of each decade being warmer than the previous”, something masked but not reversed by the current La Niña event.

Daily maximum temperatures in Australia, the report finds, have increased by 0.75°C since 1910, the annual average daily mean temperatures are up by 0.9°C over the same period, and annual average overnight minimum temperatures are up by 0.9°C.

In addition, the report states, “there has been an increase in the frequency of warm weather and a decrease in the frequency of cold weather … the frequency of extreme (record) hot days has been more than double the frequency of extreme cold days during the past two years.”

Changes in rainfall also show some worrying trends, in spite of the southern oscillation (the cycle between El Nino / La Niña periods) bringing heavy rainfall: in the North, monsoonal rains are rising, while across the south, the autumn and winter rains that drive agricultural activity are decreasing.

“Recent drying trends across southern Australia in autumn and winter have been linked to circulation changes. The causes of these changes are an area of active research,” the report says. South-western Australia is also experiencing a decreasing rainfall trend.

The study repeats predictions that over the long term, more droughts are likely, interspersed with intense rainfall events.

“The fundamental physical and chemical processes leading to climate change are well understood,” the report concludes. ®