"It's a world of empires that have lasted for centuries, cavalry charges are still used in battle, the tank hasn't been invented yet."

The Australian scientist and author goes on.

"By 1950 we're living in a world of nuclear weapons, jet aircraft and half of the global population is pretty much living under communism – in just 35 years."

It's a thought experiment the chair of the Climate Council uses to point out how "genuinely unimaginable" the year 2050 is for us now.

But with the right global approach, Professor Flannery says, it's a date by which the world could be drawing down around one part per million of atmospheric carbon per year – "a huge outcome that will really start setting us on a trajectory for healing the planet".

His comments come just days after a Greenpeace report suggested the world could transition to 100 per cent renewable energy by 2050.

Less than three months out from the United Nations' Paris climate talks, Professor Flannery is speaking on Wednesday at the University of Sydney about the need for the talks to "set the tone for the future".

The once Australian of the Year and former head of the now defunct Climate Commission said Paris could already be considered a success for "getting us out of the worst-case scenario trajectory" before it has even begun.

"I spent three years of my life chairing a Copenhagen climate council, working with the Danish government and industry to try and get a good outcome," he said, speaking of the UN Climate Conference of 2009 which ultimately collapsed.

"We saw how that failed due to failures in the political process. That won't happen at Paris: people are well prepared."

One of the most important things to be considered in Paris, he said, is shortening the review period for pledges.

Countries currently review pledges every 10 years, "but technology is changing so fast we actually need a five-year review period or something even shorter."

To Paris, Australia is taking the plan to cut carbon emissions by at least 26 per cent of 2005 levels by 2030.

In his latest book, Professor Flannery introduces new tools that could help avoid a climate catastrophe.

The tools are so new he had to invent a new name for them: "third way" technologies.

He calls them a "third way" because they are distinct from emissions reduction and geo-engineering, the other well-known approaches to tackling climate change.

"There was no name for technologies that draw carbon dioxide out of the air in a way that strengthens earth's capacity to self-regulate," he said.

Seaweed farms, used for large-scale Co2 absorption and carbon-negative cement, which captures C02 over extended periods, are some of the "third way" technologies the world should be exploring, he believes.

"I expect one of the things that will be said at Paris is that I am wrong and that there is a moral hazard in introducing discussion on these technologies at this time, because we need to be focused on emissions reductions," he said.

"My response is there [may be] a moral hazard in introducing discussion now, but there is also a hazard in not doing it. The longer we leave it to develop these technologies, the less chance we'll have them operating at scale when we really need them – from, say, 2030 onwards."

Tim Flannery will speak on Wednesday September 23, at A Global Climate Deal in 2015: What are the chances? What are the implications? from 6.00pm to 7.30pm at the Charles Perkins Centre Auditorium, Johns Hopkins Drive, The University of Sydney. Entry free, online booking required. Book online.