But the fall was slight because the drop in car use was mostly cancelled out by the increasing amount of carbon released by coal-fired power stations.

NSW bucked the national trend, emissions from coal-fired power falling 107,000 tonnes, or 0.7pc.

Victoria, which burns more emissions-heavy brown coal, accounted for most of the carbon increase.

The figures, compiled by the independent body The Climate Group, measure emissions from coal, natural gas and petrol, based on electricity use and fuel sales in NSW, Victoria and Queensland.

The Climate Group's Australian director, Rupert Posner, said: "This report shows that the good news of decreasing emissions from petroleum products has been entirely undone by another big increase in emissions from coal-fired power stations, particularly those burning the most greenhouse-intensive brown coal."

Altogether about 68 million tonnes of carbon dioxide or its equivalent was sent into the atmosphere from energy and transport over summer.

This was about 600,000t less than in the previous summer.

The amount of greenhouse gas pumped out by vehicles in NSW fell by 3.6pc on the previous year.

During the year the trend towards less road transport, which was evident the previous year, continued, even though petrol prices fell again after reaching record highs the year before.

The Victorian heatwave in the first week of last month led to surging demand for power as millions of people turned air conditioners up full blast.

But the resulting rise in carbon emissions was felt most strongly in NSW, which generated most of the extra power and exported it across the state border.

The new figures came as a study by another group, The Climate Institute, suggested that Australia's total carbon emissions had continued to rise even though the economy was staggering from the global financial crisis in the December quarter.

The Federal Government needed to set more ambitious targets for greenhouse gas cuts than the 5pc it has committed to achieve by 2020, said the institute's director, John Connor.

"This data reveals an Australian economy still highly geared to pollution needing strong new policies to clean up the economic engines so as the economy recovers we'll be growing clean jobs and a clean economy."