The strength of the Earth's greenhouse effect is determined by the concentration in the atmosphere of a handful of greenhouse gases. The one that causes the most warming overall is water vapour – though human activity affects its level in the atmosphere indirectly rather than directly. Show The greenhouse gases that humans do emit directly in significant quantities are: Carbon dioxide (CO2). Accounts for around three-quarters of the warming impact of current human greenhouse-gas emissions. The key source of CO2 is the burning of fossil fuels such as coal, oil and gas, though deforestation is also a very significant contributor. Methane (CH4). Accounts for around 14% of the impact of current human greenhouse-gas emissions. Key sources include agriculture (especially livestock and rice fields), fossil fuel extraction and the decay of organic waste in landfill sites. Methane doesn't persist in the atmosphere as long as CO2, though its warming effect is much more potent for each gram of gas released. Nitrous oxide (N2O). Accounts for around 8% of the warming impact of current human greenhouse-gas emissions. Key sources include agriculture (especially nitrogen-fertilised soils and livestock waste) and industrial processes. Nitrous oxide is even more potent per gram than methane. Fluorinated gases ("F gases"). Account for around 1% of the warming impact of current human greenhouse-gas emissions. Key sources are industrial processes. F-gases are even more potent per gram than nitrous oxide. Human activity also changes the planet's temperature in other ways. For example, vapour trails from planes, soot from fires and and tropospheric ozone created indirectly by local pollution all tend to increase warming. On the other hand, aerosol particles produced by some vehicles and industrial processes tend to bounce sunlight away from the earth, temporarily counteracting some of the warming caused by man-made greenhouse gases. The ultimate climate change FAQ This answer last updated: 23.06.2011 Related questions This editorial is free to reproduce under Creative Commons
Yes, by increasing the abundance of greenhouse gases in the atmosphere, human activities are amplifying Earth’s natural greenhouse effect. Virtually all climate scientists agree that this increase in heat-trapping gases is the main reason for the 1.8°F (1.0°C) rise in global average temperature since the late nineteenth century. Carbon dioxide, methane, nitrous oxide, ozone, and various chlorofluorocarbons are all human-emitted heat-trapping gases. Among these, carbon dioxide is of greatest concern to scientists because it exerts a larger overall warming influence than the other gases combined.  Steam billows from the Intermountain Power Plant in Delta, Utah. This coal-fired plant is operated by the Los Angeles Department of Water and Power. Photo CC license by Matt Hintsa. At present, humans are putting an estimated 9.5 billion metric tons of carbon into the atmosphere each year by burning fossil fuels, and another 1.5 billion through deforestation and other land cover changes. Of this human-produced carbon, forests and other vegetation absorb around 3.2 billion metric tons per year, while the ocean absorbs about 2.5 billion metric tons per year. A net 5 billion metric tons of human-produced carbon remain in the atmosphere each year, raising the global average carbon dioxide concentrations by about 2.3 parts per million per year. Since 1750, humans have increased the abundance of carbon dioxide in the atmosphere by nearly 50 percent. Learn more. ReferencesUSGCRP (2017). Climate Science Special Report: Fourth National Climate Assessment, Volume 1 [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi: 10.7930/J0J964J6. Friedlingstein, P., Jones, M. W., O’Sullivan, M., Andrew, R. M., Hauck, J., Peters, G. P., Peters, W., Pongratz, J., Sitch, S., Le Quéré, C., Bakker, D. C. E., Canadell, J. G., Ciais, P., Jackson, R. B., Anthoni, P., Barbero, L., Bastos, A., Bastrikov, V., Becker, M., … Zaehle, S. (2019). Global carbon budget 2019. Earth System Science Data, 11(4), 1783–1838. https://doi.org/10.3929/ethz-b-000385668 What is the most greenhouse gas emitted from human activities?Carbon dioxide from the burning of fossil fuels is the largest single source of greenhouse gas emissions from human activities.
How many total greenhouse gases are there?There are ten primary GHGs; of these, water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are naturally occurring. Perfluorocarbons (CF6, C2F6), hydroflurocarbons (CHF3, CF3CH2F, CH3CHF2), and sulfur hexafluoride (SF6) are only present in the atmosphere due to industrial processes.
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