Professor Will Steffen.

Professor Will Steffen. Photo: Alex Ellinghausen

Canberra is set to log its hottest July on record, breaking records set in the mid-1990s.

But meteorologists are predicting cooler days and higher than average rainfall for the coming months.

And climate scientists say the unusually warm July serves as a reminder of the effects of human-made climate change.

Aaron Coutts-Smith, manager of climate services at the Bureau of Meteorology, said on Tuesday Canberra this month had recorded an average maximum temperature of 13.3 degrees, compared with the 13.2 degrees average recorded in 1993 and 1994. If the temperature reaches more than 12 degrees on Wednesday, the last day of the month, he said it would be Canberra's hottest July since records began in 1939.

Canberra generally averages minus 0.1 degrees overnight in July, he said, but this year the overnight average has been 1.6 degrees.

Will Steffen, executive director of the Australian National University's Climate Change Institute, said one record-breaking month was not particularly significant in considering the impact of human activity on the climate, but it served as a reminder that the climate was warming.

''I think whether it's a record warm month or a record hot day, it does grab people's attention and I think that's a good thing,'' he said.

''But I think what needs to be done is some serious examination of the entire data record, of the underlying science, so that people get the understanding the scientific basis for human caused climate change is really strong. That's not debated.''

Professor Steffen said at least three decades of climate data needed to be considered to determine a trend and a long-term analysis shows a warming in south-eastern Australia over the past century.

''With that underlying trend of a warming climate, it loads the dice towards having record high temperatures - whether it's a day, whether it's a summer, whether it's a month,'' he said.

Mr Coutts-Smith said Canberra's rainfall in July had been close to average but there had been relatively few rainy days. High pressure systems had dominated with warm winds coming from the north and north-west.

But he said the outlook for NSW and the ACT over the next three months was for above average rainfall and cooler days and nights.

Warmer than average July temperatures were recorded in many parts of eastern Australia, with Sydney also likely to record its hottest July, recording nearly 3 degrees above the average maximum day time temperature. NSW was likely to record its third hottest July on record, recording 1.9 degrees above average during the day.

Mr Coutts-Smith said Sydney had seen a long-term trend towards warmer temperatures and was known to experience ''urban heat island effect''.

''Where you have a build-up of buildings and hard surfaces like asphalt - so roads - you can create a warming effect,'' he said.