Credit Jonathan Kingston / National Geographic/Getty Images
Carbon dioxide readings at the Mauna Loa Observatory in Hawaii have reached what atmospheric scientist Ralph Keeling calls a "psychological threshold" of 400 parts per million. The amount of carbon dioxide in the atmosphere has been steadily increasing since near-constant measurements began at the observatory in 1958.
Credit Will von Dauster / NOAA
Pat Lang, of NOAA in Boulder, Colo., measures the amount of greenhouse gases from an air sample. The Boulder lab is part of a global network of air-sampling laboratories that track carbon dioxide levels in the atmosphere.
Earth's atmosphere is entering a new era. A mountaintop research station that has been tracking carbon dioxide for more than 50 years says the level of that gas in our air has reached a milestone: 400 parts per million.
That number is one of the clearest measures of how human beings are changing the planet. It shows how much carbon we have put into the air from burning fossil fuels — and that carbon dioxide drives global warming.
This measurement comes from Mauna Loa, Hawaii, a remote volcano where the air is largely free of local influences.
I'm Michel Martin, and this is TELL ME MORE from NPR News. Now it's time for our weekly visit to the Barbershop, where the guys talk about what's in the news and what's on their minds. Sitting in the chairs for a shape-up this week are writer and culture critic Jimi Izrael, with us in Washington, D.C.
This is TELL ME MORE from NPR News. I'm Michel Martin. Coming up, even for devoted Christians reading every word of the bible may be a once in a lifetime challenge. In a minute, we'll hear from a man who decided to copy the entire book by hand. And he tells us he's not even particularly religious. We'll think you'll be intrigued by what he has to say in a few minutes.