This past summer, I took my one-year-old daughter to visit her 96-year-old great grandmother at her home in Massachusetts. It was during that week in August when climate activists threatened to disrupt flights out of Heathrow Airport. I thought they were pushing their luck, pinning the blame for global warming on a bunch of harassed holiday makers who fly occasionally, probably reluctantly, and in great discomfort. I remembered meeting an American lawyer a year before who had flown to London from California for the weekend simply because he wanted to maintain his frequent flyer status. Couldn’t they have bum-rushed his plane? I felt indignant: I’d made a flipping 90 minute documentary on climate change. I knew what my carbon footprint was when these so-called climate activists were still in short trousers.

I reflected on what a quick journey it had been – from disbelief about climate change, to a dawning realisation that it was real and a sense of hostility towards the sceptics, to the inevitable backlash; pure annoyance with the self-righteous climate zealots and a wish to prove them wrong. And that was just me.

When we started making our film about climate change, I had a vague sense that there was a likelihood that human activity had contributed to the phenomenon of global warming. By the time we finished, I was in no doubt that the evidence pointed to a real and probably disastrous man-made heating of the planet.

I came to this conclusion over the course of the film after talking to scientists and insurers, and to Inuit hunters in northern Alaska who admitted that their winters were warming but simultaneously wanted oil production to expand in the far north because they stood to profit from it. Yes, the hockey stick graph was persuasive, the one that shows the extraordinary and unprecedented increase of carbon dioxide in the planet’s atmosphere since about the time of the industrial revolution. And so was talking to scientists at Britain’s Hadley Centre. And so was meeting James Lovelock, the originator of the Gaia hypothesis, which holds that the Earth behaves like a single, self-regulating organism. Lovelock took a twinkly delight in offering the direst predictions of what was about to happen to our planet – and the dwindling likelihood that we would be able to effect any meaningful change for the better. Even the head of Shell told us that climate change was happening.