evidence: The amount of carbon dioxide in Earth's atmosphere reached 419 parts per million in May, its highest level in more than four million years, the National Oceanic and Atmospheric Administration announced on Monday. [...] Since 1958, scientists with the Scripps Institution of Oceanography at the University of California, San Diego, and later, NOAA, have regularly measured the amount of carbon dioxide in Earth's atmosphere at a weather station atop Mauna Loa. Each year, concentrations of carbon dioxide increase enough to set a new record. [...] Carbon dioxide is a greenhouse gas that remains in the atmosphere for hundreds of years. The last century of steep increases in carbon dioxide is driven almost entirely by human activity, mainly the burning of fossil fuels. The effects of climate change are already being felt, as bigger and more intense hurricanes, flooding, heatwaves and wildfire routinely batter communities all over the world.