Facing the Wind: Common Greenhouse Gases
4/9/2014, 3 p.m.
Carbon dioxide: Carbon dioxide is the primary greenhouse gas that is contributing to recent climate change. CO2 is absorbed and emitted naturally as part of the carbon cycle, through animal and plant respiration, volcanic eruptions, and ocean-atmosphere exchange. Human activities, such as the burning of fossil fuels and changes in land use, release large amounts of carbon to the atmosphere, causing CO2 concentrations in the atmosphere to rise.
Ocean-Atmosphere Carbon Cycle: As global warming and ocean acidification continue, the world's oceans may start to absorb less from the atmosphere. If less is absorbed by the oceans, more would accumulate in the atmosphere, causing greater warming. This is another example of a positive feedback.
Human activities currently release over 30 billion tons of CO2 into the atmosphere every year. This build-up in the atmosphere is like a tub filling with water, where more water flows from the faucet than the drain can take away.
Methane is another GHG produced through both natural and human activities. It is more abundant in Earth’s atmosphere now than at any time in at least the past 650,000 years. Due to human activities, CH4 concentrations increased sharply during most of the 20th century and are now more than two-and-a-half times pre-industrial levels. In recent decades, the rate of increase has slowed considerably.
Nitrous oxide is produced through natural and human activities, mainly through agricultural activities and natural biological processes. Fuel burning and some other processes also create N2O. Concentrations of N2O have risen approximately 18% since the start of the Industrial Revolution, with a relatively rapid increase towards the end of the 20th century. In contrast, the atmospheric concentration of N2O varied only slightly for a period of 11,500 years before the onset of the industrial period, as shown by ice core samples.