"I don't think we're losing the argument," insists Natalie Bennett, sitting in her London office.
"We've seen a dip but we're going to see a steady rise again."
It's been a difficult period for the green movement. There was a time about six years ago when public concern with climate change was at an all-time high.
News bulletins regularly led with catastrophic warnings about global warming and world leaders clambered over each other to be seen to be doing something about it.
Even a young David Cameron got in on the act, posing with huskies and promising to lead "the greenest government ever".
Fast forward six years and the issue has fallen right down the political agenda. So what's changed?
"It's entirely understandable," explains Bennett.
"And it's not just the climate change deniers and petrochemical companies throwing huge amounts of money into the debate, we've also had a huge economic crash.
"And it's perfectly understandable that when people are really worrying about paying for tomorrow's lunch or next week's rent or next month's mortgage payment, it's very hard to focus on the bigger picture of the world of ten or 20, or 50 years time."
She claims that recent environmental disasters and the debate over fracking are beginning to turn public attention back on to the issue.
Even Conservative voters are turning, Bennett insists.
"I've been down to Balcombe myself and I've met several members of the local Tory party who were supporting the protest camp and in some cases supporting it quite significantly in terms of money and food and all the rest of it. There is very considerable resistance there in Balcombe."
She says the issue taps into wider public distrust with politicians.
"I was speaking to a woman down in Balcombe. She'd probably voted Tory most of her life and she said to me: 'I don't understand why politics is failing me so much. Why no-one will listen to me. What shall I do?'
"And that is the place where huge numbers of people are."
So far the Green party has failed to capitalise on that feeling. Despite electing their first MP, their national poll numbers are still slumped at around two per cent.
And while Ukip have arguably joined the political big league, the Greens appear to be getting squeezed.
I ask whether their left-wing economic policies are turning off voters like the Conservative-leaning woman she met in Balcombe.
Is the characterisation of the Greens as a "watermelon" party - green on the outside, but red in the middle - preventing them from forming a broader coalition of support?
"We seem to get lots of fruit comparisons," she says, laughing.
"If it's not the watermelon, it's the mangos and the guavas and some other fruits I probably haven't caught up with yet.
"But the fact is the green philosophy and way of looking at the world to my mind produces an inevitable kind of economics as well as inevitable view of what should be done about water voles and forests and things like that.
"We are a wealthy society in Britain and if we're going to live within the limits of our planet then some people are going to have to get more and some people at the top are going to have to get less and that means that the economics and the environment go together.
"You can't separate the two."
She admits that holding on to the party's only parliamentary seat in Brighton Pavilion against Labour will be "a hard struggle" but is convinced Caroline Lucas can do it.
"I think any reasonable observer would agree that Caroline Lucas has been an excellent MP."
One of those perhaps not entirely convinced of this fact is the local Green party leader of Brighton council, Jason Kitcat.
Earlier this year Lucas joined a sit-in protest against Kitcat's handling of a pay dispute with refuse workers.
The workers launched wildcat strikes which led to rubbish piling up on the streets and calls from party members for the resignation of Kitcat.
There was also disquiet among green activists about Bennett's handling of the situation.
Did she try to intervene?
"Look I understand where both sides are coming from and the situation in Brighton is that we're not running the country. We'd be running it very differently if we were and and Brighton council budget would be in a very different position.
"We understand when you're running things you've got difficult positions and decisions to make and that's the nature of these things.
"And I hope we're in a position where we have that problem in 30 places where we're running 30 councils."
I suggest that people looking at the situation in Brighton might reasonably think twice about electing another Green council.
"I'm sure people understand that they have had bin strikes before under both Labour and Tory administrations and so nobody is claiming that we can come in as the Green party with a magic wand which just solves all problems.
"We do grown-up politics."
Speaking of grown-up politics, I ask whether she would ever consider working with Ed Miliband in the event of a hung parliament.
"That's an interesting question," she says, a little stumped.
"I think Tony Blair who took us into the Iraq War was deeply problematic but I don't think on current evidence that Ed Miliband is as problematic as Tony Blair was."
What about Cameron?
"I cannot imagine the circumstances in which we would go into coalition with the Tories but beyond that there is an interesting model which the Scots employ which is a confidence and supply model.
"And that means you can ensure there is stable government but you can still vote according to your principles... that might mean that you don't get the ministerial car but it would mean you could sleep a little more comfortably at night."
She says the party has grown up in other ways.
Trained as a scientist, Bennett insists the party has moved away from what some have described as their "anti-science" policies on animal rights and alternative medicine.
"We've looked at our science policies over the past few years and we've rewritten them substantially and anyone who formed a view on our science policy five years ago, I would urge them to take a fresh look at what our policy is now."
I ask her about her views on homeopathy.
"Well, what we say is that if evidence can be shown to say this treatment is worthwhile then that's what the judgement should be made on. We're not making any judgements based on any ideological approach to medicine. We're just saying look at the evidence."
These feel like weasel words. Surely as a scientist she can make a judgement on whether homeopathy works?
"I'm on the record as saying I absolutely do not believe in the explanations for homeopathy and how it quote unquote works," she says, before adding: "But I do believe in the placebo effect and it's possible that if a placebo is the best treatment for a lower back pain, for example, then that's what the evidence shows and in a lot of these areas there hasn't been enough research done to really tell that.
"So I don't believe in homeopathy but that doesn't mean that I say that it shouldn't be allowed to exist."
I ask her about the involvement of the Green party's first member of the House of Lords Jenny Jones in the recent Flour Out protest.
Jones had joined the protesters as they threatened to destroy research into GM food.
As a scientist, does she support such anti-scientific action?
"I support what she did in that particular case because they were trying to put something out there loose and the problem with GM is that once they're gone they're gone and you can't get them back.
"The gene cannot be put back in the bottle."
So what's next for Bennett? Does she plan to join her colleague Caroline Lucas in getting arrested at fracking protests?
She laughs. "I may or may not get arrested in the future but I don't think I will be following Caroline in doing that.
"I think as Caroline said when she was arrested, sometimes it's very very hard under our very strained non-functioning political system to get your voice heard."
And what about her own career? Under Green party rules, leaders are elected on strict two-year terms.
She says she intends to stand again for another term but thinks she "might be pretty tired" after four years.
Isn't that quite a short time for a party leader?
"In the Green party we don't regard the whole thing as a greasy pole," she says smiling, "but as a pleasant green field in which we can all pass the ball between each other.
"We're like a very cooperative football team," she adds.
And with that I leave her to her captainship, as she gets ready for their party conference in Brighton.
Top of the agenda is how to get the Green team out of the lower leagues.