If there is one thing guaranteed to get our temples throbbing, it is hearing a politician explain that £12 million is not a lot of money. But someone has to do it so, with apologies for all the numbers, here goes …

You’re in the city centre. You fancy a cup of coffee and a slice of cake in a café: £5 gone in a few mouthfuls.

There are 200,000 of us living in York. If we all have a cake and a coffee we’ve spent a million pounds. Do that once a month and York residents have spent £12 million in one year, without even noticing.

We are all pants at macroeconomics. We understand the value of fifty pence or fifty pounds but we’re hapless halibuts at understanding big numbers, because most of us don’t have millions sitting around.

We all understand the point of pooling our wealth to invest in things that benefit us all. We cheerfully share lampposts, roads and public swimming pools.

And, strangely, when it suits us we’re good at turning a jelly eye to big numbers. The city is planning to spend £38 million widening five miles of the York Outer Ring Road. That’s £7.6 million per mile just to make journeys a few minutes faster. Yet there aren't many people shouting angrily about that.

What has this got to do with tackling climate change, you ask? Simple; climate change is very big. And the solutions will be just as big.

Individuals who croon that everything can be sorted with solar-powered patio lighting, bicycles, and a Sunday roast ban are as fluffy-headed as those who pretend climate change isn’t real.

Feeble fantasy greenwashing is everywhere. Most local authorities, businesses, and politicians of all parties, plump for the ostrich manoeuvre: head in sand, muffled mumbling.

I don’t want to rain on anyone’s parade but putting solar panels on the roofs of 100 houses is not ‘leading the way on climate change’.

To create the zero carbon York most of us want, we must get serious. We must quantify exactly how big the challenge is and we must be honest about the cost to fix it. We need a proper plan for the whole city, not a few token schemes to soft-soap our collective shame.

Good news. Some of the big data already exists. We know, for example, the total cost of electricity bills across York and, from that, the total kilowatt hours of power consumed and CO2 produced from electricity in York.

Similar data is available for gas bills and for fuel sold on petrol station forecourts.

What about diesel used by agriculture, oil-based central heating, food miles, etc?

With expert help, we are working on it.

Once we know where we are, we can chart a course towards a zero carbon city. With a serious and coherent ten year action plan for the city that all the stakeholders buy into – council, politicians, businesses, public services, academic institutions, unions, residents, conservation groups, faith communities – we will finally be able to deliver real change.

Because the figures are huge the solutions, and the savings, will also be huge.

For example, if homes on York Central are built to passivhaus standard then they’ll have heating bills of only £60 a year. Imagine if all 83,000 York homes were as energy efficient.

Say we currently each spend £700 a year on heating; that’s £58 million a year on heating. If our homes were all passivhaus standard that total bill would be just £5 million, an annual saving of £640 per home. And a massive cut in carbon emissions.

Don’t expect that transforming all those homes, improving public transport, and rethinking food production will be cheap; they will cost many hundreds of millions of pounds. But with a coherent plan we can borrow to invest in the knowledge that those changes will pay back and secure our common future.

There are plenty of great examples of cities that are successfully doing just that. We’re happy to spend a fortune shaving a couple of minutes off an outer ring road trip; surely we can do the same to protect our future?

But wait, say the contrarians. What if we spend all that money, reduce pollution and fuel poverty, clean up our rivers and seas, protect wildlife, create new forests, build warmer homes, improve public health, reduce traffic congestion … and climate change turns out to be exaggerated? What a waste.

Really?