THERE'S a joke Christian Vassie tells to satirise those who insist there's no such thing as climate change so we don't need to clean up our act.

An environmental campaigner is standing on a soapbox, outlining the action needed to save the planet: "Reduce fossil fuels, protect our forests and wildlife, clean up our oceans, cut pollution, increase biodiversity, plant more trees..."

A sceptic in the audience starts heckling. "But what if climate change is a hoax and we waste our time making the world a better place for nothing?" he shouts.

The chair of York's new climate change committee can't help giving a wry grin as he recites this. There's a point to it, Cllr Vassie stresses. Even in the very unlikely case that the world's scientists have got it wrong and we're not contributing to a global catastrophe that could ruin the lives of our children and our children's children - even then, it would still be worth trying to clean up our planet. Because future generations would have a much more pleasant world to live in. One which might, for example, still contain wild elephants as well as beef cattle...

The science, however, very strongly suggests that we are contributing to global climate change - and that if we don't stop, our behaviour will change the world in ways our children really won't thank us for.

A report from the Intergovernmental Panel on Climate Change (IPCC) last autumn warned that even if we manage to limit global warming to a maximum of 1.5C above pre-industrial levels - an effort which will require 'unprecedented changes in all aspects of society' and 'rapid and far-reaching changes' in land use, energy production, industry, buildings, transport and cities - we still face increased flooding, drought, extreme heat and the death of up to 90 per cent of the world's coral reef.

Fail to keep the global temperature rise to that 1.5C level and let temperatures rise even half a degree more and the consequences could be dire, the report warned: global sea-levels 10cms higher than at 1.5C levels, with correspondingly worse flooding; the Arctic regularly free of sea ice in summer; the almost complete eradication of all coral reefs...

Earlier this year, in a BBC programme entitled simply 'Climate Change: The Facts', naturalist and broadcaster Sir David Attenborough put it even more starkly.

"The scientific evidence is that if we have not taken dramatic action within the next decade we could face irreversible damage to the natural world and the collapse of our societies," the 92-year-old said.

City of York Council appears to have taken these warnings on board. On March 29 this year, it declared a Climate Emergency, and set York the ambitious target of becoming a zero-carbon city by 2030.

Cllr Vassie, a Liberal Democrat, sees his new climate change committee's job as being to signpost how York can achieve that.

He's never made any secret of his environmental concerns. Back in 2008 he wrote a children's book - Three Little Pigs and the Straw Stick House - which turned the story of the three little pigs on its head. In Cllr Vassie's version, the pigs shivering in a poorly-insulated brick house have to go out to the coal shed for more fuel in the middle of winter - where the big bad wolf is waiting, and promptly gobbles them up. The pigs living in a warm, well-insulated house built of straw bales are able to stay snugly indoors, however, and survive the winter...

The book was a cry from the heart for us to find more energy-efficient ways of building new houses. But then Cllr Vassie has always been impatient with our tendency to do things a certain way just because that's always how we've done them, arguing for more radical approaches to transport and to protecting the environment.

His outspoken approach put some backs up even in his own party last time he was a councillor. In charge of the culture portfolio from 2007 to 2009 during the last Liberal Democrat administration in York, he left the Executive following public rows with members of his own group. He then lost his Wheldrake seat to a Conservative in the 2011 election.

Now he's back. And, while he's not on the Executive in York's new Lib Dem/ Green coalition, his role as chair of the climate change committee is a key one.

He sees his committee's job as being to scrutinise council policies and decisions to assess their impact on emissions - and to produce a ten-year Climate Emergency action plan that will enable the city to reach its ambitious 2030 zero-carbon target.

It won't be easy, he admits. Even those who accept the extent of the climate emergency can be overwhelmed by the sheer scale of the challenge.

Which is why we all need to work together, he says. No one person can halt climate change. "So we have to find common causes, and pool our resources."

In York, he sees the city council as the 'bigger us' - the collective organisation representing the city's people that has the power to work with other organisations and with businesses to get things done.

But he says if we're serious about reducing carbon emissions to zero by 2030, local politicians of all persuasions need to pull together. "All parties need to be signed up to it," he says. "They all need to be sharing responsibility, and then sharing the kudos for whatever we achieve."

At the moment, his committee includes Lib Dem, Green and Labour councillors. He'd like to see Conservatives and Independents on it, too - and also to co-opt some experts on wildlife, biodiversity and sustainability. He hopes then to produce a yearly report, charting the city's progress towards the zero carbon goal, that is signed off every year by all parties.

Perhaps stung by his earlier experience in office, he's keen to stress that he doesn't speak on behalf of the council itself. "I am communicating what I think is important, what I think needs to be done," he says.

But, as the climate change committee chair, he's happy to set out his own ideas on what he hopes the council can achieve.

If the authority is to carry the city's residents with it, we will need some quicker fixes, where people can see progress being made, he says. But we mustn't shirk from the tougher challenges, either.

Here are four of his ideas so far...

A ring of wildflowers around the city walls

The daffodils which adorn the grass banks beneath the city walls in early spring are lovely, he says. But they don't last long. So why don't we seed the banks with wildflowers that would bloom later in the year? The flowers would take over after the daffodils die back, providing a haven for bees and other pollinators and insects, increasing biodiversity. "It would also look spectacular, a dazzling sea of colour." And it needn't be expensive, he says: just a few thousand pounds to buy enough seed to sow all around the walls.

Plant more trees

He's not an expert on trees, he admits: but there are plenty of people who are. There's the 'Northern Forest' initiative, which aims to plant 50 million trees in a broad swathe across the north of England over the next 25 years. And in York there is Treemendous, a volunteer-led organisation supported by the council which, since 2010, has planted thousands of trees in the city. So he would like to see the city setting an ambitious target for tree-planting, and co-opting other organisations and enlisting the help of volunteers to make sure it happens.

Vertical farms

If we're to stand any chance of York being carbon-neutral by 2030, it is vital that big developments - and especially York Central - are properly sustainable, Cllr Vassie says. That means lots of eco homes, preferably built to passivhaus standards so they require very little energy to heat or cool; cheap, well-integrated public transport; and more. One idea he has already floated is that of 'vertical farms'. Essentially greenhouses in which growing plants are stacked in six or seven layers on top of each-other, they're well-established in the Netherlands. In high density areas where land is precious, they're a great way of increasing growing space, he says. And they allow food to be grown locally, instead of being brought in from elsewhere, so are good for the environment.

Trams

Yes, a modern tram system would be expensive, Cllr Vassie admits. But other British cities have them. And so do many smaller continental cities, such as Dijon.

We need to be willing to change our way of looking at things, Cllr Vassie believes - and be willing to invest in a long-term future, rather than always looking for short fixes. York is, after all, the city that built York Minster - a generations-long project. In the bigger scheme of things, a £200 million investment, financed by borrowing, to give York the modern, integrated transport system it so badly needs, isn't that much, he insists. We just need the collective will to make the investment.

Dijon invested in its future, and its 12.5-mile tram system, a public/ private partnership built with the help of a 200 million Euro loan from the European Investment Bank and consisting of two lines and 37 stations, opened in 2012.

The city that built York Minster should be able to do the same. "But if we sit here and say 'who is going to fund this?', we'll still be sitting here in 20 years time..."