Greenhouse gas emissions and atmospheric concentrations have increased over the past 150 years
Emissions of several important greenhouse gases have increased substantially since large-scale industrialization began in the mid-1800s. During the past 20 years, about three-fourths of human-caused (anthropogenic) emissions came from burning fossil fuels. Concentrations of carbon dioxide (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), emissions have exceeded the capacity of these processes to absorb carbon.
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 40% since the mid-1800s.
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, these changes are commonly referred to as climate change.
Assessments by the Intergovernmental Panel on Climate Change (IPCC) suggest that the earth’s climate has warmed 0.85°C (1.53oF), from 1880 to 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."
Did you know?
Fossil fuels supplied about 82% of the primary energy consumed in the United States and were responsible for about 94% of total U.S. carbon dioxide emissions in 2013.
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 past 22,000 years."