National Geographic : 2017 Apr
7 THINGS YOU NEED TO KNOW El Niño added to last year’s record by temporarily releasing heat from the Pacific. But no natural cause explains the half-century warming trend. The sun’s output cycles up and down every 11 years; volcanic eruptions sporadically cool the planet. Meanwhile human-emitted greenhouse gases form a steadily thickening blanket that traps heat at Earth’s surface. More than nine out of 10 climate scientists agree: Carbon emissions cause global warming. We’ve known about the greenhouse effect since the 1800s. Swedish physicist Svante Arrhenius even predicted in 1896 that carbon dioxide from coal burning would warm the planet. He saw it as a good thing—and just how bad it will be is debatable. But it’s real, and it’s dangerous. 2 IT’S BECAUSE OF US. 3 WE’RE SURE. Change We need energy—food, fuel, electricity—to lead modern lives. Billions of people need more of it. But how we get energy is changing the Earth in ways that threaten us all. Can we find a better way? Climate change isn’t a hoax or a scientific conspiracy, it’s a grand challenge. Here are the facts. Carbon dioxide on Earth A NASA satellite has been mapping the changing amounts of carbon dioxide in Earth’s atmosphere. In this image derived from data collected in October 2014, swirls of CO2 emitted by burning fossil fuels in the Northern Hemisphere are clearly visible. Average atmospheric carbon dioxide in parts per million 300 1911 284 1832 400 2016 350 1987 31 In 2016 annual average CO2 concentrations exceeded the threshold of 400 parts per million.