The report, The Critical Decade 2013, to be released on Monday, paints a grim picture of the future for the ACT as a result of unchecked climate change, including a rising death toll from extreme-heat days, dwindling inflows to the city's major water storages and further reductions in winter and spring rainfall.

''The decisions we make from now to 2020 will largely determine the severity of climate change our children and grandchildren experience,'' the report states.

The CSIRO and the Bureau of Meteorology predict the number of days where the temperature climbs above 35 degrees in Canberra will rise from the current long-term average of 5.2 days a year to eight by 2030 and between 10 days and 18 days by 2070, depending on the action taken.

One of the report's two authors, Professor Will Steffen, said many of the predictions climate scientists made in the 1970s and '80s were becoming reality as communities began to suffer more-damaging storms, major bushfires and prolonged droughts.

''Canberrans hardly need reminding about the devastation bushfires can cause. If you look at the data since about 1973, 16 of the 38 observation stations show the fire danger rating has increased, while the remainder haven't gone down. Of particular importance for Canberra is that most of those 16 stations are in the south-east corner and Canberra's right in the middle of that,'' Professor Steffen said.

Meeting global targets to limit temperature increases to 2 degrees meant the world would have to commit to using no more than 20 per

cent of the estimated fossil fuel reserves still available.

''We are at a crossroads. If we want to meet the 2 degree target we've got to really get cracking on that, and that means leaving most of the stuff in the ground,'' Professor Steffen said.

Changes in rainfall meant summer rains could increase in Canberra, but in terms of the number of extreme-heat days the ACT was already experiencing nearly double the long-term average.

The already endangered northern corroboree frog is also likely to be placed under further pressure, and the number of frosts in Canberra could decrease by up to 27 per cent by 2050.

But Professor Steffen said the tangible evidence of climate change had led to a change of attitude in the community and he was hopeful there would be further action.

''Humanity has always met challenges by changing behaviour and innovating, otherwise we would still be using stone tools. It's not too late to make the necessary changes.''