On the phone from Cygnet, an hour south of Hobart, Bob Brown tells me he opens his new book with this quote from Bertrand Russell: “The trouble with the world is that the stupid are cocksure, but the intelligent are full of self doubt”. It’s a theme that recurs throughout our conversation. Especially at a time when it seems the world is dead-set going down the gurgler. But the point of using Russell’s statement, and of the book itself – called Optimism: reflections on a life of action – is the opposite of a slump-shouldered-everything’s-a-mess-what-can-I-do-about-it? attitude. It’s about activism. “People who believe everybody’s equal are much more likely to be restrained in what they say than bullies, extroverts and cheats,” says Brown. “Those people have to get over it. They’ve got to stand up and speak out and take on the bullies. No good sitting back and being miserable.”

In 2012 Bob Brown retired from his role as federal leader of the Australian Greens and from the senate position he held for 16 years.

Before politics, Brown was a doctor and an activist. In 1978 he was the leader of The Wilderness Society and was instrumental in the campaign to save the Franklin River from a proposed dam. He was put in prison for his trouble. He became a member of the Tasmanian parliament in 1983 and introduced a number of private member’s bills including lowering parliamentary salaries, advocating for a nuclear-free Tasmania and gay law reform. In 1987 he introduced a bill to ban semi-automatic rifles. But it was “laughed down” just nine years before the Port Arthur massacre. After the tragedy, John Howard put forward an almost exact piece of legislation, which saved, what Brown says are, “hundred of lives”. There are many such anecdotes in Optimism.

After politics Brown was the chairman of Sea Shepherd for just over a year. And he has set up The Bob Brown Foundation, which supports front-line environmentalists.

“I didn’t retire to do nothing,” he says. “I’m very motivated to talk to as many people as possible about how we collectively can do a lot better. And I mean all seven billion people on the planet. Because we’re all sharing a common future, and a common destiny.” It’s this kind of empathetic, straight-talking that cuts through politics and brings the big issues back to people and our environment.

So here is Bob Brown, in his own words.

On overcoming shyness
As I’ve gotten older I’ve gotten more confident about speaking out. As a youngster I was saddled by being gay in a country where any homosexual activity was illegal. And I was also saddled with a very strong belief in doing the right thing – I was a Presbyterian. And I became very, very shy. I found it impossible to get up and give a speech. The Franklin River changed all that because I got involved in the campaign to save it. I was talking about something else – not about myself, but about the river.

On optimism
You can be optimistic or you can be pessimistic – take your pick. I was pessimistic when I was young and I didn’t like it. I found it was a mindset which prevented action. I think optimism is a weapon in itself. It’s certainly good for people in business, so why shouldn’t it be used by people who are planning to give the planet and the people coming after us, and indeed other creatures on the planet, a fair go?

I have an optimism that we can use our collective intelligence to turn around the current rush to global warming, acidification of the ocean, spread of cities, loss of farm lands, loss of forests, extinction of species and so on.

On working together
My optimism comes out of a very real understanding of our malfunctioning human society. We’re a herd of seven billion mammals on the planet and we’re making a mess of it, and we don’t need to. But key to changing that is recognising that we have the same destiny. We’re in an age when everybody knows what everybody else is doing, we’ve got mass communications like never before. We’re all in this together and we share what the future’s going to be. And we’ve got to get out of the selfish mindset, which divides humanity instead of uniting us.

On priorities
We’ve got to get out of the age of materialism. And I put a capital “M” on that in the book – it’s a new religion – which has overtaken all the other religions and which has got us by the throat. The god of Growth – which I speak about in the book (capital ‘G’ for growth) – has to be obeyed. We have to keep using more, absorbing more, buying more, expanding more. On a finite planet. And you don’t have to be Einstein to know that can’t keep going.

Ecology first. If we don’t have a viable, world, a viable biosphere, then economic wellbeing is not going to be much use to us. Some predictions are that we’ll be consuming 300 per cent more of the planet by the end of this century if the current projections keep going like they are. We’re collectively not aiming at a sustainable planet, and that’s why the world’s forests are being destroyed at a great rate. Why the world’s fisheries are collapsing, why our waterways are more polluted than ever before and why there is less food-producing land than ever before. It’s being taken over by cities, highways gas-extraction plants and so on.

On politics
This is the best-educated public ever, but, at the election last year, it voted for accelerated climate change and I enjoy talking about that because I think most people know that and they feel conflicted. You pick up the Murdoch media, for example, and you see climate scepticism, punishment of progressive thinkers and admonishment of environmentalists because they are getting in the way of progress. People need a counter-voice to that. I’m just one small counter-voice currently in the wilderness of growth and economics. But we’re a growing crowd and we have common sense on our side.

On activism
I’m a globalist and a citizen of the earth, and that rings all sorts of danger bells for those who are currently in power and don’t want to share it.

Jenny Weber, from our foundation, went to Doha (Qatar) a month ago to campaign against Tony Abbot’s request that the United Nations take World Heritage Listing off Tasmania’s tall eucalypt forest. It didn’t get through because there was such a strong campaign from Australian environmentalists, including our foundation. And I’ve just put out a call for the Tarkine Wilderness – the largest temperate rainforest in Australia in north-west Tasmania. It’s threatened by mining and logging and I’m very keen to help the environmentalists there who are up against Labor and Liberal parties who want the place shredded by what are currently 39 mining applications. So we’ve got a lot to do.

On leadership
Politics is about leadership and about defying the power elite who have taken over the world. It is about everybody having an equal say in the future. And I have faith in that. Politicians should take leadership. But, ultimately, we have to put our faith in the people, and not in those who are wielding power. When people vote for abolishing climate-change action – I accept that. I’m a democrat. I think collectively, we can think it out. We just need the leadership to turn that into action. And there’s big forces against it. And I take great pleasure in taking it on.

The Wheeler Centre presents Bob Brown: On Optimism on Tuesday 5 August. Bookings at wheelercentre.com. He will also be appearing at the Melbourne Writer’s Festival. Details at mwf.com.au. Bob Brown’s book, Optimism: reflections on a life of action is out now.