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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 (measured in carbon equivalent terms), 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 have increased by about 43% since 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 0.85 degrees Centigrade (1.53 degrees Fahrenheit) between 1880 and 2012 and that human activity affecting the atmosphere is likely an important driving factor. The IPCC’s Fifth Assessment Report (Summary for Policymakers) states, "Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."

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In 2019, fossil fuels were the source of about 80% 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.

The report later states, "It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together."

The report also states, "Concentrations of CO2, CH4, and N2O now substantially exceed the highest concentrations recorded in ice cores during the past 800,000 years. The mean rates of increase in atmospheric concentrations over the past century are, with very high confidence, unprecedented in the last 22,000 years."

Last updated: December 8, 2021