Carbon dioxide is the gas that animals (including humans) exhale. It is a food for plants and without it no plant can grow. Carbon dioxide is also produced while burning wood, gas or other fossil based fuels. Small amounts of carbon dioxide in the air are harmless. However, recently changes in weather patterns, known as global warming, have raised concerns. There is a strong belief that due to increased level of carbon dioxide, the trapped heat cannot pass through the atmosphere into space. This causes a rise in the ambient temperature on Earth known as the greenhouse effect.

 Some scientists fear that the rise in temperature will disrupt weather patterns, causing the polar icecaps to melt and release more water into the ocean. This increase in water level might cause two things to happen (1) the ocean's saline concentration would weaken, threatening marine species, and (2) coastal areas would flood.