If you've ever tried to tell people about 350.org, you've probably heard this question before: "What's 350?" No, it's not "almost a circle" or a popular baking temperature, you've had to answer. It stands for 350 parts per million. That's the safe level of CO2 in the atmosphere according to the latest science.
Thanks in large part to all the great organizing you've done around the world, more and more people are seizing onto this 350 target as a simple, scientific way to explain the climate challenge we face.
Today, the New York Times published a front-page story all about the history of "parts per million" and the scientist who first started measuring the concentration of greenhouse gases in our atmosphere. The article begins: