Greenhouse Gas Levels About to Hit Bad Milestone Carbon dioxide ratio in atmosphere close to symbolic 400 parts per million By John Johnson, Newser Staff Posted May 1, 2013 7:07 PM CDT Updated May 4, 2013 6:50 PM CDT 263 comments Comments Smoke pours out of chimneys at a cement plant in Binzhou city, in eastern China's Shandong province, earlier this year. (AP Photo) (Newser) – We're probably going to hear a lot about the "Keeling curve" and references to "400 parts per million" in the coming weeks. The curve measures the ratio of carbon dioxide in the Earth's atmosphere, and that ratio is about to cross the 400-ppm level for the first time in, oh, 3 million to 5 million years, reports the LA Times. Scientists at the Scripps Institution of Oceanography are now offering a daily look at the rising number at this website, or you can follow along via Twitter here. "I wish it weren't true, but it looks like the world is going to blow through the 400-ppm level without losing a beat," says a Scripps geochemist. "At this pace we'll hit 450ppm within a few decades." Which will mean a hotter planet and rising sea levels, says another of the scientists. “Our dumping of heat and CO2 into the ocean is like making investments in a pollution bank."