CO2 emissions

Carbon dioxide () is an important long-lived trace gas in Earth’s atmosphere currently constituting about 0.04% (400 parts per million) of the atmosphere. Despite its relatively small overall concentration, is a potent greenhouse gas and plays a vital role in regulating Earth’s surface temperature through radiative forcing and the greenhouse effect: absorbs and emits infrared radiation at wavelengths of 4.26 µm (asymmetric stretching vibrational mode) and 14.99 µm (bending vibrational mode). Carbon dioxide is essential to life on Earth and is an integral part of the carbon cycle, a biogeochemical cycle in which carbon is exchanged between the Earth’s oceans, soil, rocks and biosphere. Biologically, plants and other photoautotrophs extract carbon from the atmosphere in the form of carbon dioxide by the process of photosynthesis and use it as an energy source and for the construction of their body parts. Therefore, Earth wouldn’t have a present-day biosphere without atmospheric . Carbon dioxide is well mixed in the Earth’s atmosphere and reconstructions show that concentrations of in the atmosphere varied from as high as 7,000 parts per million during the Cambrian period about 500 million years ago in ancient-Earth biospheres to as low as 180 parts per million during the Quaternary glaciation of the last two million years. The recent phenomenon of global warming has been attributed primarily to increasing atmospheric concentrations in Earth’s atmosphere. The global annual mean concentration of in the atmosphere has increased markedly since the Industrial Revolution, from 280 ppm to 395 ppm as of 2013, with the increase largely attributed to anthropogenic sources, particularly the burning of fossil fuels. The daily average at Mauna Loa first exceeded 400 ppm on 10 May 2013. It is currently rising at a rate of approximately 2 ppm/year and accelerating. An estimated 30–40% of the released by humans into the atmosphere dissolves into oceans, rivers and lakes. which contributes to ocean acidification. The present concentration of in Earth’s atmosphere is the highest in the past 800,000 years and likely the highest in the past 20 million years.Climate Change 2001: The Scientific Basis As recently as 2007, scientists reasoned that concentrations could be safely allowed to reach 550 parts per million, but more recent research produces a scientific consensus that “urges the world to reduce atmospheric carbon dioxide concentration to about 300 parts per million by volume” NASA climatologist Gavin Schmidt, however, once told statistician and writer Nate Silver that neither of them would ever see a year in which carbon dioxide concentrations would go down, not ever, nor would their children.