evidence: One such family of chemical compounds is chlorofluorocarbons (CFCs), whose contribution to depleting ozone in Earth’s upper atmosphere has led to large springtime decreases in ozone around Earth’s polar regions, especially over Antarctica, a phenomenon known as the ozone hole that was first reported in 1985. But, as NASA atmospheric scientist Nathaniel Livesey explains, today, thanks to the phase-out of CFCs, Earth’s ozone hole is in recovery. He says the turnaround provides a great example of what humans can do when they work together to solve a global atmospheric problem. [...] Livesey says Earth’s recent temperature increases simply cannot be explained without accounting for human emissions of carbon dioxide, which builds up over time and has a long life once emitted into the atmosphere. To those who claim that carbon dioxide, methane and other greenhouse gases don’t have a significant impact on global warming, he offers a simple scientific experiment. "Take a gallon of water and put a drop of food coloring in it. You’re going to immediately notice a change," he said. "The same is true for adding trace greenhouse gases to the atmosphere. It doesn’t take very much of an increase before their presence literally changes the color of the atmosphere as observed by infrared satellite instruments."