From the link:
...this week is probably the last time you or me or anyone now alive on planet Earth will ever see concentrations of CO2 lower than 400 ppm. Ralph Keeling published a short piece about it, here. Unless something fundamentally changes in our relationship with the atmosphere (such as developing and deploying effective artificial carbon sequestration), the gas’s long-term accumulation will keep rising, and the planet will keep hanging on to a little more heat than it used to the year before. Though “400” is simply a round number with no inherent particular significance in and of itself, passing it for good seems a valid enough reason to pause for a moment and reflect on this massive thing we’re doing to our planet. Every additional increment of CO2 is likely to be a moderately long lived addition to our atmosphere. Its heat-trapping capacity is a major force driving our climate system into new, uncharted terrain for a long time to come. We depend on our climate. People we will never meet on the other side of the world do, too. Our children will depend on it. Grasshoppers and bluebirds and rattlesnakes and whales depend on it. Fungi depend on it. Grasses depend on it. Coccolithophores depend on it. And though this should be obvious, I’ll go ahead and say it explicitly: to a greater or lesser extent, we depend on them. Everything’s interdependent. We all live downstream – and we’re polluting that stream.