The last time Earth had comparable levels of atmospheric carbon dioxide was about three million years ago, during the mid-Pliocene. Back then, global average temperature was about 3.6–5.2°F (2–3°C) warmer than it is today. Sea levels were also higher, by about 15–25 meters. And while passing 400 parts per million permanently — or hitting a high of 410 parts per million, as happened on Tuesday — won’t trigger any immediate climate consequences, it is a stark reminder of the profound influence human activity is having on the planet.That's sea levels higher by 50 to 80 feet. And a 3 degree Celsius increase doesn't sound like much but it means a very different planet than we are now experiencing.
|The Keeling Curve. CREDIT: Scripps Institute of Oceanography|
As you can see that CO2 curve is accelerating. It needs to be stopped now, not next year or the next decade. We will be living with the level we now have which if the pliocene is any indication, is going to be bad enough, but if we don't stop now, it's going to get a lot worse, unimaginably worse.