English: This image shows an analogy between filling a bathtub with water and the increasing concentration of carbon dioxide in Earth's atmosphere. From the public-domain source - US Environmental Protection Agency (US EPA, 2012): "If the amount of water flowing into a bathtub is greater than the amount of water leaving through the drain, the water level will rise. Carbon dioxide (CO₂) emissions are like the flow of water into the world's carbon bathtub. "Sources" of CO₂ emissions such as fossil fuel burning, cement manufacture, and land use are like the bathtub's faucet. "Sinks" of CO₂ in the ocean and on land (such as plants) that take up CO₂ are like the drain. Today, human activities have turned up the flow from the CO₂ "faucet", which is much larger than the "drain" can cope with, and the level of CO₂ in the atmosphere (like the level of water in a bathtub) is rising."