Something hit the gas. The concentration of carbon dioxide in the atmosphere in 2016 jumped to its highest level in 800,000 years, according to the U.N. World Meteorological Organization. Scientists say the surge — 50 percent greater than the last decade’s average annual increase — was caused by a combination of human activity and a strong El Niño event. El Niños and other extreme weather phenomena are likely to happen more often as the planet warms up. Researchers are urging global leaders to step up enforcement of the Paris climate deal.