It's official, our atmosphere now contains more carbon dioxide (CO2)—the chief greenhouse gas—than it has for the past three million years. The Mauna Loa Observatory (MLO), perched high on the shoulder of 13,677-foot Mauna Loa on Hawaii's Big Island, recorded 399.72 parts per million (ppm) of carbon dioxide last Thursday. At times throughout the day, levels surpassed 400 ppm.
The last time there was this much CO2 in the air—during the Pilocene epoch, some three million years ago—planetary temperatures rose an average of 3 to 4 degrees, and the world's oceans swelled up to 40 meters (131 feet) higher than they are today (enough water to submerge most of Manhattan).
Carbon dioxide is a chemical compound that's found naturally in our environment, for example from volcanic eruptions or the respiration of living organisms. However, through activities like logging oxygen-rich forests and burning fossil fuels, humans have aggravated a delicate balance, pouring vastly larger quantities of CO2 into the atmosphere, which traps heat energy from the sun the same way a greenhouse window does (hence the name greenhouse gas). In fact, 2012 was the hottest year on record in the U.S. by an entire degree Fahrenheit.
Carbon dioxide levels have been rising steadily since measurements began at Mauna Loa in 1958, when the level was about 317 ppm. Though several polar monitoring stations have recorded the 400 ppm benchmark in the past year, the Mauna Loa findings are considered the most concrete.
In a new report titled The Critical Decade: Global Action Building on Climate Change, the Australian Climate Commission has reported on some of the leading countries taking steps to reduce greenhouse gas emissions. China, the world’s largest contributor to greenhouse gases (the U.S. is second), is taking major steps to reduce its carbon footprint, having increased wind power generation by 50-fold since 2005, and solar power capacities by 75% in 2012 alone. The U.S., on the other hand, still trails many of its counterparts in the developed world in that it hasn't been able to enact and enforce nationwide energy efficiency appiance and building standards, renewable energy targets or effect a carbon pricing plan, or reach consensus on an emissions reduction target a la the Kyoto protocol.
With renewed efforts from U.S. leadership in concert with other world leaders, humans may yet be able to curb the rise of greenhouse gases and restore out atmosphere to safe, stable levels, but we don’t have long to do so.
Scientists hold that at 450 ppm—which at this rate we're likely to see in just a few decades—earth’s biosphere has only about a 50-50 chance of correcting the kind of formidable climate changes that will lead to global food and water crises.