A definitive report on observed changes in long term trends in Australia’s climate has been released today by CSIRO and the Bureau of Meteorology.
Bureau chief executive Dr Rob Vertessy said temperatures across Australia were, on average, almost 1°C warmer than they were a century ago, with most of the warming having occurred since 1950.
“Australia’s mean temperature has warmed by 0.9°C since 1910,” Dr Vertessy said.
“Seven of the 10 warmest years on record in Australia have occurred since 1998. When we compare the past 15 years to the period 1951 to1980, we find that the frequency of very warm months has increased five-fold and the frequency of very cool months has decreased by around a third.
“The duration, frequency and intensity of heatwaves have increased across large parts of Australia since 1950.
“Extreme fire weather risk has increased, and the fire season has lengthened across large parts of Australia since the 1970s.
“We have also seen a general trend of declining autumn and winter rainfall, particularly in southwestern and southeastern Australia, while heavy rainfall events are projected to increase. Australian average annual rainfall has increased slightly, largely due to increases in spring and summer rainfall, most markedly in northwestern Australia.”
CSIRO chief executive Dr Megan Clark said Australia has warmed in every state and territory and in every season.
“Australia has one of the most variable climates in the world. Against this backdrop, across the decades, we’re continuing to see increasing temperatures, warmer oceans, changes to when and where rain falls and higher sea levels,” Dr Clark said.
“The sea-surface temperatures have warmed by 0.9°C since 1900 and greenhouse gas concentrations continue to rise.”
CSIRO and the Bureau of Meteorology play a key role in monitoring, measuring and reporting on weather and climate, contributing to improved understanding of Australia's changing global climate system. State of the Climate 2014 is the third report in a series and follows earlier reports in 2010 and 2012.
The full report is available at www.bom.gov.au/state-of-the-climate/
Following is a summary of the findings. For example, over the past 15 years, the frequency of very warm months has increased five-fold and the frequency of very cool months has declined by around a third, compared to 1951-1980.
Sea-surface temperatures in the Australian region have warmed by 0.9°C since 1900.
Moreover, rainfall has increased since 1900, with a large increase in northwest Australia since 1970.
The duration, frequency and intensity of heatwaves have increased across large parts of Australia since 1950.
Finally, a wide range of observations show that the global climate system continues to warm. It is extremely likely that the dominant cause of recent warming is human-induced greenhouse gas emissions and not natural climate variability, the report said.
Ice-mass loss from the Antarctic and Greenland ice sheets has accelerated over the past two decades.
The Earth is gaining heat, most of which is going into the oceans. Global mean sea level increased throughout the 20th century and in 2012 was 225 mm higher than in 1880.
Rates of sea-level rise vary around the Australian region, with higher sea-level rise observed in the north and rates similar to the global average observed in the south and east.
Ocean acidity levels have increased since the 1800s due to increased CO2 absorption from the atmosphere.
Finally, atmospheric greenhouse gas concentrations continue to increase due to emissions from human activities, with global mean CO2 levels reaching 395 ppm in 2013.
Global CO2 emissions from the use of fossil fuel increased in 2013 by 2.1 per cent compared to 3.1 per cent per year since 2000.
The increase in atmospheric CO2 concentrations from 2011 to 2013 is the largest two-year increase ever observed.
As a result of these findings, the report said Australian temperatures are projected to continue to increase, with more hot days and fewer cool days.
Average rainfall in southern Australia is projected to decrease, with a likely increase in drought frequency and severity.
While tropical cyclones are projected to decrease in number (but increase in intensity), projected sea-level risea will increase the frequency of extreme sea-level events