"I think if we're going to reduce carbon in the atmosphere we've got to move to nuclear power, but that's not likely to happen - so we'll just keep burning coal," Mr Smith said.

Mr Smith said Australia exports about $100 billion worth of fossil fuels every year.

"If we stop doing that, the economy will collapse," Mr Smith said.

"We're very fortunate that Australia exports the fossil fuels of coal and gas and that we have mineral reserves like iron ore. That will probably keep growing as China and India raise their standard of living."

He doesn't believe the world will act decisively on climate change "unless there's some catastrophe".

"Then we'll have to stop using fossil fuels."

He said renewables were "fantastic, but they are intermittent".

"The problem is storage. We haven't yet found a cheap way of storing power," he said.

Nevertheless, the Climate Council [an independent organisation] said recently that Australia was "on the cusp of an energy storage boom driven by supportive policies" and that "the cost of energy storage solutions is falling rapidly".

And economist Ross Garnaut wrote in his new book Superpower that: "I have no doubt that intermittent renewables could meet 100 per cent of Australia's electricity requirements by the 2030s, with high degrees of security and reliability, and at wholesale prices much lower than experienced in Australia over the past half dozen years".

However, Mr Smith believes that plans to increase the world population by four billion would "make it impossible to fix climate change".

He said this would be "unbelievably terrible for mankind, but that's how life works".

"There's been lots of civilisations before ours - the Romans, Phoenicians and Greeks - that have failed.

"The only successful people were the Australian Aboriginals. They've lived here for 60,000 years. They never had more than 1 million people."

He said Australia now had 25 million people and "we're on our way to 26 million".

Mr Smith made his name and money as the founder of Dick Smith Electronics, Dick Smith Foods and Australian Geographic. As well as being a philanthropist, he is also a political activist.

For several years now, he's been raising awareness about his population concerns.

He said the reason Australia's population was growing at a record rate was "we have such enormous numbers of immigrants every year".

The Australian Bureau of Statistics estimated that Australia's net overseas migration was 249,700 people for the year to March 2019.

"I'm very pro-immigration, but at a normal level of 75,000 a year," Mr Smith said.

Opponents to Mr Smith's overpopulation concerns say migration reduces inequality and increases Australia's long-term economic performance, competitiveness and living standards.

Mr Smith has this week taken out big advertisements in national media that state "eternal growth in a finite world is impossible".

"Our economic system requires perpetual growth and that's not possible," he said.

"It is the elephant in the room. The government talks about growth all the time. They actually mean growth in population and using resources and energy. That's what our system of capitalism requires. But it's impossible. You can't grow forever."

Mr Smith believes rising population trends would mean "we'll get lots more poorer people".

"World population is going from 7 billion to 11 billion [by 2100]. That's horrendous. In Australia, we're on our way to 100 million [the ABS estimates up to 50 million by 2066]," he said.

He said Australia had high levels of youth unemployment and underemployment, "where young people can't get the job they want".

"That will just increase with robotics and automation. They'll be less jobs in the future, not more," he said.

"We should live in balance like Germany, Italy and Japan. I've benefited enormously from the typical growth we have now and people say I shouldn't say anything about this."

It would be easier for him to say nothing, but he said "I'm concerned about our grandchildren".

"You can't have the type of growth we've had for the last 150 years - it's impossible to have that for the next 150 because the world is finite," he said.

He opposes forced population control.

"We should be concentrating our international aid on educating families, especially young women. Once young women are educated, they have less kids. Once you raise the standard of living, people voluntarily have less children," he said.

"If you stop growing, you don't have to build more and more houses. You can then concentrate on making everything better. That's what the Japanese are doing. They're going from 120 million to 90 million by 2060.

"They are making their high-speed rail even faster and better. We could start making Australia's railways more modern and faster."

He said high-speed rail could be built between Newcastle, Sydney and Canberra, but then the area would need tens of millions of people.

"Or, would you rather have what it is now - a good, high-quality standard of living," he said.

Mr Smith's comments follow the release of the Gateways to Growth report this week, which said Newcastle, Wollongong and Geelong were three regional cities "perfectly positioned" for growth.

The report called for a "stable source of transparent funding for ongoing investment" for the regions, which could "support a larger population on the eastern seaboard, while easing overpopulation and congestion in the big cities".

Dudley resident Don Owers also has concerns about population.

Mr Owers, a conservationist, cited plans like Lake Macquarie City Council's 2050 strategy, titled Planning Our Future.

"It's all about growth - 50,000 more people by 2050 and probably more due to what is called growth 'spill-over' from the Sydney region," he said.

"Imagine Australia and the Hunter in an era of stable population. Lake Macquarie would not have to sacrifice greenfield sites like Pinny beach to provide housing.

"Newcastle could have retained the Joy Cummings plan for development of the harbour. Views would not have been obstructed by high rise. The rail line could have been put underground - it would have been cheaper than light rail - leaving a nice green space in the city.

"Brownfield sites like the Pasminco land could become parks, food gardens or forests. Houses would once again become affordable and our huge mortgage debt would diminish, leaving us less exposed to a financial collapse."