Peter Kalmus sits outside California's Pasadena City Hall in his electric car. His sons, aged 10 and 12, are on steps of the grand building, waving signs with the slogans: "School strike for climate" and "Adults, act like it!"
Kalmus' Tesla is just the kind of luxury you'd expect a climate scientist at NASA's jet propulsion laboratory to have. But he doesn't exactly live a lavish lifestyle. Actually, he says, he usually cycles. He hasn't been on a plane since 2012, and he eats a vegetarian diet.
As someone who works in climate science, Kalmus feels there's no excuse not to reduce his carbon footprint. "This is an urgent crisis," he says. "Those of us who understand that should act like it's an urgent crisis."
Which is why he wrote "Being the Change: Live Well and Spark a Climate Revolution," a book with the message that we all have our bit to do, and lifestyle changes protect the climate don't have to be radical.
Small changes add up
Kalmus grows his own fruit and veg, keeps bees and used to run a car on waste vegetable oil. Other than that, his life is pretty much like that of any US American. But he has had to persuade those around him to get on board.
"I've had to shift expectations both with my extended family and also with my work," he explains. "We hike more, we take more vacations locally. In California, there are lots of options for being out in nature as opposed to flying to a far-flung destination."
By normalizing a lower-carbon lifestyle, Kalmus hopes to inspire others, even if the individual changes they make are small.
"I realized that if you try to make other people change, it doesn't usually work that well. You can't force anyone else to change. If they see you changing and smiling about it, they'll think 'that's not so bad' and they'll start to change, too."
And small changes can add up to something much bigger, Kalmus believes.
"As more and more people start to change in their own lives it's going to have an effect on all the people around them and that's going to pave the way for collective action by shifting the culture," he says.
More urgent than you think
One of the challenges to getting people to shift their behavior is that climate change can seem a remote concern, so long as our lives tick by unaffected.
"Sometimes, when it's a beautiful day, it can feel like it's far away and that it's a problem just for the future," Kalmus says. "But it's here now. If you don't think it's urgent, it's more urgent than you think."
On the flip side, the urgency — and scale of the crisis — means many of us feel our individual actions won't make much difference. That's another notion Kalmus wants to challenge.
Read more: More dire data, less climate change concern?
"There are a million things we can do," he says. "When I see other people acting, that's what gives me hope. I think we're in the middle of a huge social shift, possibly a tipping point on social action on climate change."
Hope in a new generation
Last year, 16-year-old climate activist Greta Thunberg started skipping school on Fridays to strike for climate justice outside the Swedish parliament. Now, young people around the world are following her lead and making Friday a day of regular student protest. It's the kind of movement that gives Kalmus hope.
"I don't think the social environment was ready for the school strikes," he says. "There's a major shift. Things could change very rapidly from here, I think. The thing that's driving this increasing awareness is that climate change is getting worse, and that disasters are getting worse."
Read more: Germany's new green youth
Anyone deeply involved in the science of climate change will admit the future can look pretty bleak. "It still affects me sometimes," Kalmus says. "But for me, the key thing to do is to act, and to basically do all we can and that transforms something that could lead you into despair or depression into something incredibly meaningful."
Right now, that meaningful action is coming from his own children, as they join together with other young people across the globe to stand up for the future of their planet.