Another year of extreme weather brought the Philippines a super typhoon and the United States the widest tornado ever observed, deadly wildfires, severe drought and killer floods. President Barack Obama released his plan to battle climate change and its impact on people and wildlife, but the warming planet passed another troubling milestone as heat-trapping greenhouse gases continued to accumulate. Here is a look back at some of the most significant events to affect the environment in 2013.
• Carbon dioxide: Recorded carbon dioxide levels in the atmosphere reached the unsettling milestone of 400 parts per million on May 10, a level of the heat-trapping gas unseen for 3 million to 5 million years. The burning of fossil fuels is primarily responsible for the increase. In 1958, when scientists began monitoring the carbon dioxide level in the air atop Mauna Loa volcano in Hawaii, it was at 316 parts per million. Other scientists reported, however, that the rate of increase in emissions slowed.
• Tornadoes: A rare EF-5 tornado in Moore, Okla., on May 20 killed 25 people, injured hundreds and obliterated more than 1,000 homes along a 17-mile path of destruction. The storm reached speeds of more than 200 miles per hour, killing seven third-graders in an elementary school when a wall collapsed on them. A few weeks later, the deadly El Reno, Okla., tornado was measured as the widest ever.
• Chimpanzees: A U.S. Fish and Wildlife Service proposal in June to protect both captive and wild chimpanzees under the Endangered Species Act threatened to end their online trade and use as medical lab specimens. But the National Institutes of Health took the added step of retiring all but 50 chimps in its stable of 400 as subjects of biomedical research, a practice that started early in the past century. NIH said new technologies made their use unnecessary, but the decision followed years of denunciation and action from animal rights activists.
• Oil pipeline: President Obama unveiled his long-awaited climate action plan on June 25, ordering the Environmental Protection Agency to propose limits on carbon dioxide emissions from existing coal- and gas-fired power plants. He also said he would approve the Keystone XL pipeline, which would carry crude from Canadian oil sands fields to refineries in the Gulf of Mexico, only if it did not “significantly exacerbate” climate change. The State Department is still reviewing comments it received on a draft environmental analysis of the Keystone pipeline that it issued in March.
• Flooding: Severe, widespread flooding in Colorado killed five people and prompted the biggest civilian airlift since Hurricane Katrina in 2005. Searchers sought more than 1,200 people who were missing or stranded. More than nine inches of rain fell in Boulder, Colo., over a 24-hour period Sept. 11 and 12.
• Global warming: It’s “extremely likely” that humans are the main cause of global warming, the Intergovernmental Panel on Climate Change said on Sept. 27. The past three decades have been the hottest since 1850, and carbon concentrations in the atmosphere are up 40 percent from that year. For the first time, the international panel of scientists established a budget for the amount of carbon that can be released into the atmosphere but said emissions will have a negative impact even if the budget target is reached.
• Wildfires: The Yosemite Rim Fire was scary not only because it burned for two months ending Oct. 25 and ranked as the third-largest wildfire in the history of California, a state that has seen its share of monster burns. It followed a giant Arizona wildfire that killed 19 elite firefighters, the Granite Mountain Hotshots, in June. On top of that, it followed what meteorologists say was the driest year ever in California, where Death Valley tied the record for the highest temperature ever in June, 129 degrees. Los Angeles and San Francisco posted their driest year on record, says Christopher Burt, a weather historian of Weather Underground.
• Typhoon: Haiyan, dubbed a “super” typhoon, struck the Philippines Nov. 7 with sustained maximum winds of 195 mph and gusts of 235 mph, one of the most intense storms in modern times. Nearly 4 million people were forced from their homes, and the death toll has reached 6,000, with more missing.