What Is CO2?
Carbon dioxide (chemical name CO2) is a clear gas composed of one atom of carbon (C) and two atoms of oxygen (O2). CO2 is just one of many chemical forms of carbon on the Earth. The near-surface environment of the Earth contains approximately 121,000,000 GtC (gigatons of carbon); a gigaton is equivalent to a billion metric tons; the number means "121 million gigatons or 121 million billion metric tons" of carbon). When a ton of carbon combines with oxygen, it makes nearly four tons of CO2 gas.
Carbon dioxide is a significant greenhouse gas. Since the Industrial Revolution, anthropogenic emissions - including the burning of carbon-based fossil fuels and land use changes (primarily deforestation) - have rapidly increased its concentration in the atmosphere, leading to global warming. It is also a major cause of ocean acidification because it dissolves in water to form carbonic acid..
We are currently putting 40 billion tons of CO2 into the atmosphere every year. It’s almost impossible to grasp what 40 billion tons means. A cubic kilometer of water weighs a billion tons, but it’s hard to imagine a cube 3.5 kilometers (2.2 miles) on a side—the equivalent amount of water weighing 40 billion tons. The largest class of aircraft carrier weighs about 100,000 tons, but picturing 400,000 of them still strains the imagination (not to mention vaporizing them into the air every year).