I wasn't expecting it to be so much fun.
I mean, this is serious. If we can't persuade governments to act decisively to reduce carbon emissions, global warming is going to fry us to a crisp.
That's why I joined the Time to Act on Climate Change march on the 7th of March. 'I'm marching because our precious beautiful planet is all we've got - and it would be such a tragic waste if we trashed it,' I glumly declared on the train up to town.
But already, catching up with my Transition Town pals, the animated chat, the sense of common purpose were starting to cheer me up. One of them had told her mum she was going on the climate change march. "That's nice, dear. Are you for or against it?" her mother had replied. I was starting to feel slightly hilarious.
I sat on a bench and ate a sandwich, companionably discussing TTIP with a lady I'd never met before, while enjoying the spectacle of a semi-naked Legolas-lookalike dancing to a drum.
Back with my group, I found we'd been joined by other Transition Towns - hurrah! And finally we were off, inching our way onto the streets crammed with 20,000 others, proudly holding our banner and leading the Transition Town block.
There were inventive costumes - polar bears, a dragon even - and slogans: "What part of catastrophic and irreversible is it that you don't understand?" "I'll vote UKIP when the renewable energy runs out." And many more.
Rather less joyful were the armed police guarding the closed gates of Downing Street, though the row of ordinary bobbies in front of them seemed affable enough.
So on past Westminster then to Parliament Square, where a host of speakers inspired and energised us. Passionate declarations of solidarity from trade unionists; the Lancashire anti-fracking Nanas; a video message from Naomi Klein (urging us to spread the word before the Paris Climate Conference in December), a beaming Caroline Lucas (if only all our MPs were like her) and finally Laurel, a 12-year-old girl who belted out the message to Westminster loud and crystal clear
I left the march in a happy haze. Sometimes I really do think we can pull this off. And if not, we can have plenty of fun trying.