Mashable: The amount of carbon dioxide in the Earth’s atmosphere has exceeded 402 parts per million (ppm) during the past two days of observations, which is higher than at any time in at least the past 800,000 years, according to readings from monitoring equipment on a mountaintop in Hawaii. Carbon dioxide, or CO2, is the most important long-lived greenhouse gas responsible for manmade global warming, and it is building up in the atmosphere due to the burning of fossil fuels such as coal, oil and natural gas….