Four hundred parts per million. It's just a number, but it speaks volumes. Humanity's unchecked extraction and release into the atmosphere of ancient, naturally sequestered carbon (a.k.a. fossil fuels) is driving us into uncharted climatic territory. According to the Mauna Loa Observatory, we have hit that milestone, and show no signs of slowing down.
Put another way, we've increased the atmospheric concentration of carbon dioxide by 25 percent in 100 years. And if we continue at the present accelerating consumption rate, which all signs indicate we will, we should hit 450 ppm in 2040.
But images speak louder than words. You may have already seen the widely distributed wiggly climbing Keeling Curve comprised of the 55-year record at Mauna Loa Observatory on the Big Island of Hawaii. Here's what you get when you tack on 250 years of ice core data onto that: