Australian scientists say carbon dioxide levels in the atmosphere are now higher than at any time in the past 800,000 years.
The scientists, from the Commonwealth Scientific and Industrial Research Organisation, say the past decade in Australia was the warmest on record.
Their annual State of the Climate report, released on Wednesday, says Australia's annual average daily maximum temperatures have increased by 0.75 °C since 1910.
The temperatures are forecast to rise by between 1 °C and 5 °C by 2070.
However the report says 2010 and 2011 were the coolest years recorded since 2001 because of two consecutive La Nina events.
They say the amount of carbon in the atmosphere has reached 390 parts per million; they have been unable to find any previous evidence of level exceeding 300 parts per million.