CO2 levels reach 3 million-year high

In a grim milestone for our warming planet, atmospheric carbon dioxide levels have reached their highest level in more than 3 million years. Sensors at the Mauna Loa Observatory in Hawaii recorded that concentrations of CO₂—the greenhouse gas most responsible for climate change—reached 415 parts per million last Friday. In the 800,000 years before the Industrial Revolution, CO₂ levels never surpassed 300 ppm; they have risen 2.5 ppm annually for the past decade. The last time there was this much CO₂ in the atmosphere was during the Pliocene Epoch, between 5.3 million and 2.6 million years ago, when sea levels were about 50 feet higher than they are now. Scientists warn that if greenhouse gas emissions aren’t curbed, CO₂ levels could hit 500 ppm within 30 years. “None of these specific numbers are really thresholds in the sense that anything particular happens when we cross them,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, tells NBCNews.com. “But as we go through them, we are putting our foot on the accelerator of climate change, and impacts and damage will continue to rise.” In a timely reminder of the extreme effects of greenhouse gas emissions, a heat wave in Russia pushed temperatures in the northwestern city of Arkhangelsk to 84 degrees Fahrenheit in mid-May—30 degrees higher than the monthly average.

AP, Christian Sinibaldi/Guardian/Redux, Reuters ■