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Energy and the environment explained Greenhouse gases and the climate

Greenhouse gas emissions and atmospheric concentrations have increased over the past 150 years

Emissions of several important greenhouse gases that result from human activity have increased substantially since large-scale industrialization began in the mid-1800s. Most of these human-caused (anthropogenic) greenhouse gas emissions were carbon dioxide (CO2) from burning fossil fuels.

Concentrations of CO2 in the atmosphere are naturally regulated by many processes that are part of the global carbon cycle. The flux, or movement, of carbon between the atmosphere and the earth's land and oceans is dominated by natural processes like plant photosynthesis. Although these natural processes can absorb some of the anthropogenic CO2 emissions produced each year, starting in about 1950, CO2 emissions began exceeding the capacity of these processes to absorb carbon.

An illustration of the global carbon cycle.

This imbalance between greenhouse gas emissions and the ability for natural processes to absorb those emissions has resulted in a continued increase in atmospheric concentrations of greenhouse gases. Concentrations of CO2 in the atmosphere in 2021 were about 44% greater than the concentrations in 1850.

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Greenhouse gases warm the planet

Scientists know with virtual certainty that increasing greenhouse gas concentrations tend to warm the planet. In computer-based models, rising concentrations of greenhouse gases produce an increase in the average surface temperature of the earth over time. Rising temperatures may produce changes in precipitation patterns, storm severity, and sea level. Collectively, this is commonly referred to as climate change.

Assessments by the Intergovernmental Panel on Climate Change (IPCC) suggest that the earth’s climate warmed 0.92 degrees Centigrade (1.66 degrees Fahrenheit) between 1880 and 2012 1 and that human activity affecting the atmosphere is likely an important driving factor. The IPCC Sixth Assessment Report, (Chapter 3: Human Influence on the Climate System) states: "It is unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times."

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In 2020, fossil fuels were the source of about 79% of U.S. primary energy consumption, 94% of total U.S. carbon dioxide emissions, and 80% of total U.S. greenhouse gas emissions resulting from human activity.2

The report later states: "The likely range of human-induced warming in global-mean surface air temperature in 2010–2019 relative to 1850–1900 is 0.8°C–1.3°C." The report also states: "The current rates of increase of the concentration of the major greenhouse gases (carbon dioxide, methane and nitrous oxide) are unprecedented over at least the last 800,000 years. Several lines of evidence clearly show that these increases are the results of human activities."

1 Intergovernmental Panel on Climate Change, Sixth Assessment Report, Chapter 2: Changing State of the Climate System, Box 2.3.
2 U.S. Energy Information Adminstration, Monthly Energy Review, November 2022, and U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020, April 2022.

Last updated: December 21, 2022 with most recent data available at the time of update.