The most vulnerable people would be impacted the first and hardest, she said.

"Children bear the least responsibility for climate change but they will bear the brunt of the health impacts," Dr Charlesworth said.

Sydney will host on Sunday what is expected to be its biggest day of climate action protest as world leaders gather for the United Nations climate summit COP21 in Paris.

Dr Charlesworth will be marching for the Royal Australasian College of Physicians under a banner stating "Doctors for Climate Action".

"As a doctor and as a mother there's nothing more important that I can be doing at the moment than picking up on climate change. Doctors, paediatricians and public health physicians have a responsibility to speak out on issues that impact on health," she said.

"In 10 years' time our children are going to say, 'Mum, did you know about this? What was everyone doing?

"I need to be able to look my children in the eye and say that I did everything that I could both professionally and personally."

Hundreds of thousands of people are expected to turn out in eight capital cities around Australia to march over the weekend.

The People's Climate March starts in the Domain at 1pm and will proceed down Macquarie Street to the Opera House with marchers calling on the Australian government at the summit to demand an end to the use of fossil fuels and a much more rapid shift to renewable energy.

Among those addressing the crowd will be lord mayor Clover Moore and climate activist Professor Tim Flannery.

The march will be attended by a hugely diverse range of Australians including firefighters, faith communities, unions, farmers, health professionals, businesses, artists and musicians.

Ms Moore was to tell the conference that COP21 was the most important gathering of national leaders in our lifetime and that the future of the planet our children and their children will inherit depended on it.

She was to say: "We're already seeing the impact of accelerating climate change – bushfires, droughts, soaring temperatures, hurricanes, huge storms, floods, unseasonable warm or cold summers and winters.

"Global warming must be kept below two degrees – if not we create an environment far outside the range ever experienced by humanity with huge areas of the planet becoming uninhabitable because of flooding, drought and heat. We'll have dangerously wild weather and world food supplies will be critically endangered, resulting in millions – or even billions – of refugees.

"At the City of Sydney, we've been playing our role. And our work shows that ambitious targets are possible and compatible with strong economic growth. It needs bold leadership and courageous action."

* Queensland is wiping out so much bushland that Australia is highly unlikely to meet its 5 per cent climate pollution reduction target by 2020 if it is not stopped, the Wilderness Society said after the Queensland government today revealed 296,324 hectares of bush was cleared in 2013-14.

"Land clearing in Queensland is completely out of control again," said Wilderness Society national director Lyndon Schneiders.