Millie always asks me to talk about our name for a minute, so excuse me if you’ve heard this before. Our group is called 350 because this is a number that’s essential to life on this planet. Throughout human history, we’ve had about 280 parts per million of carbon in our atmosphere. As we’ve used radically more fossil fuels in the last hundred years, that number has climbed and climbed. And scientists know that in order to have a stable climate, we have to be below 350 parts per million—maybe even lower.