It may be a colourless, odourless and completely natural gas, but carbon dioxide is beginning to cause us a lot of problems. It only makes up a tiny fraction of the atmosphere (0.04% of all the gas by volume – or 395 parts per million) but it has a huge effect on the Earth’s temperature. That's because unlike nitrogen or oxygen, carbon dioxide molecules absorb the Sun's heat rays even though they let light rays pass through, like a greenhouse.
Scientists are looking at ways to modulate the global temperature by removing some of this greenhouse gas from the air. If it works, it would be one of the few ways of geoengineering the planet with multiple benefits, beyond simply cooling the atmosphere.
Every time we breathe out, we emit carbon dioxide just like all other metabolic life forms. Meanwhile, photosynthetic organisms like plants and algae take in carbon dioxide and emit oxygen. This balance has kept the planet at a comfortably warm average temperature of 14C (57F), compared with a chilly -18C (0F) if there were no carbon dioxide in the atmosphere.