evidence: Carbon dioxide is naturally in the air: plants need it to grow, and animals exhale it when they breathe. But, thanks to people burning fuels, there is now more carbon dioxide in the atmosphere than anytime in the past 15 million years. Most of this CO2 collects in the atmosphere and, because it absorbs heat from the sun, creates a blanket around the planet, warming its temperature. But some 30 percent of this CO2 dissolves into seawater, where it doesn't remain as floating CO2 molecules. A series of chemical changes break down the CO2 molecules and recombine them with others. [...] The main effect of increasing carbon dioxide that weighs on people's minds is the warming of the planet. Some geoengineering proposals address this through various ways of reflecting sunlight—and thus excess heat—back into space from the atmosphere. This could be done by releasing particles into the high atmosphere, which act like tiny, reflecting mirrors, or even by putting giant reflecting mirrors in orbit! However, this solution does nothing to remove carbon dioxide from the atmosphere, and this carbon dioxide would continue to dissolve into the ocean and cause acidification.