Earlier this week I helped launch the 100% London campaign to get our capital running entirely from clean energy, rather than polluting fossil fuels, by 2050. Meanwhile world leaders are heading to Paris to try and reach a desperately needed agreement to slow down the now close-to-terrifying pace of global warming.
Cities consume 75% of the world's energy and are responsible for four-fifths of all greenhouse gases. That's why all cities, not just the more obviously green ones such as Sydney or Vancouver, have a responsibility to shift to renewable energy.
This is an issue I've been passionate about for many years. In 2005, as a local campaigner before I was elected to Camden council, I helped promote Greenpeace's brilliant decentralised energy campaign to councillors there - something that was way ahead of the curve. And in 2007, as principal speaker of the Green Party, I helped launch (and wrote a foreword to) Mayor Ken Livingstone's first action plan on climate.
In that document, I said we must work hard "to make sure the ideas in this document are implemented, not left on the shelf next to the fine words and empty promises of the past".
Has that happened? London has made some important progress since then. We have reduced our emissions, but not by enough. We helped found the C40 network of world megacities committed to addressing climate change. Community energy has really grown as an idea in recent years and it's amazing to see the growth in new co-ops across the city putting solar panels on schools, churches and other community rooftops. It's also reassuring to see that the new Thameslink platform spanning Blackfriars Bridge has been stylishly covered in solar panels - a real contrast to St Pancras International station's empty roof, built before we had a proper strategy for London.
But we have also seen backsliding, especially in recent years. London is way behind on solar power compared with the rest of the country, and it's frankly embarrassing to be on the train North and whizz past villages covered in solar panels, when in the capital they are as rare as hen's teeth. Our Victorian and Edwardian terraces are still overwhelmingly not insulated. The congestion charge area has got smaller. Zombie road-building ideas (such as the terrible plan to build a £1 billion Silvertown Tunnel) are coming back to life. Electric car charging points have remained underdeveloped on our current Mayor's watch. And air pollution levels have barely changed in a decade.
It's clear now that London has lost leadership on climate change and, as a proud Londoner who has always wanted to live in one of the most active cities on this issue, that upsets me.
Climate chaos will have a practical impact on all our lives. I suspect many Londoners, particularly if like me they live in a fourth floor flat on relatively high ground, look at pictures of flooded rural towns on the news and feel sympathy but also relief that we're not as affected in London.
But for hundreds of thousands of us here, this is only thanks to the Thames Barrier, and this was closed 48 times in 2014, compared with just four times throughout the Eighties. At this rate we will need something bigger and better very soon, and if we don't take the greatly increased need to use it in recent years as a hint that something is very wrong with our climate, we are being grotesquely unfair to future generations.
In the past few weeks both Charlotte Church and Prince Charles have been criticised for saying that climate change is one of the underlying reasons for the conflict in Syria. For some reason it has been decreed bad taste to say this, especially in the case of the prince, so soon after the Isis terrorist attacks in Paris. But that doesn't mean these points are not at heart right. And if people in Europe are alarmed by the shift in population from the Middle East, imagine what it will be like when the entire population of the sub-sea-level Netherlands is eventually flooded out.
We are now getting ready for the elections for the London Mayor and Assembly and a recent survey of Londoners by campaign group Here Now found that 71% want Boris Johnson's successor to take bold steps to tackle air pollution and climate change. This race is therefore being billed as the greenest election ever.
I hope this serious attention means that policies like insulating a million homes, establishing an Energy for London department in City Hall (like Transport for London) to co-ordinate the London-wide deployment of smart, clean energy, getting gas guzzlers and diesel vehicles off our streets, or developing 'closed-loop' manufacturing so that more material is reclaimed from waste and put to new economic use, become inevitable.
But the fact that everyone is talking green doesn't mean we have won the battle. In the past few days, Conservative candidate Zac Goldsmith has made some bizarre remarks about bus lanes and cyclists while Labour's Sadiq Khan has bullishly insisted he wants to press on with entirely unnecessary new runways on the same day as boasting that he will be London's greenest mayor ever.
I say if you want green you should vote Green - you get two preferences on the Mayoral ballot and your second vote acts as insurance so there need be no worries about letting the wrong person in by putting us first. I hope that with a strong Green challenge in this election and a hard push from environmental campaigns large and small, we will see a race to the top on the environment in this election, not a backwards slide to the bottom.
London should be leading the way on climate change, transport, efficient homes, waste and clean energy. Our capital is rightly proud of being a 21st-century global metropolis, and that means we have a duty to set an inspiring example to the rest of the world.
Sian Berry is the Green Party candidate for Mayor of London and heads the party's list of London-wide candidates for City Hall