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Climate science

State of Play:

What began as a theory in the 1890s — that industrial emissions of carbon dioxide could increase global temperatures — had progressed to a scientific fact a century later. Scientists across a range of disciplines are studying the impact of the still-growing concentration of carbon dioxide and other so-called “greenhouse gases” in the atmosphere as they call for industrial and governmental policies to slow, then halt, the warming of the planet. 

What is the greenhouse effect?

The Earth’s temperature is modulated by atmospheric gases that allow the penetration of the sun’s radiation while trapping the warmth radiated from the planet’s surface. This phenomenon is known as the greenhouse effect because of its similarity to the way a greenhouse allows sun to enter and then traps the resulting warmth.

The “natural” greenhouse effect — warming not caused by human activities — increases average surface temperatures by 59 degrees Fahrenheit (33 degrees Celsius). But scientists have long theorized — now supported by unmistakeable evidence — that human activity, primarily the burning of fossil fuels and other industrial processes are adding carbon dioxide and other so-called “greenhouse gases” at unprecedented rates, likely warming the planet at a rate and to levels never experienced by human beings.

What are the primary greenhouse gases, and what are their sources?

Carbon dioxide, methane, nitrous oxide, and fluorinated gases are the primary contributors to global warming, according to the U.S. Environmental Protection Agency.

Carbon dioxide (CO2) is emitted from the burning of fossil fuels; it is removed — that is, stored or sequestered — by plants’ normal biological processes.

Methane is released through the production of coal, natural gas and oil, as well as livestock and the decay of organic waste.

Nitrous oxide is emitted via agricultural and other land use, industrial activities, and the combustion of fossil fuels.

Fluorinated gases are emitted during a variety of household, commercial and industrial activities. 

What is the status of greenhouse gas emissions in the United States?

While the effort to put in place regulations for carbon dioxide emissions remains a work in progress, the United States has shown modest reductions in overall greenhouse gas emissions between 1990 and 2020.

In that time period, overall greenhouse gas emissions have declined by 7.3 percent, according to the U.S. Environmental Protection Agency:

  • carbon dioxide emissions are down 7.9 percent.
  • methane emissions are down 16.7 percent.
  • nitrous oxide emissions are down 5.4 percent.
  • fluorinated gas emissions are up 89.8 percent.
     
What is the Intergovernmental Panel on Climate Change?

The IPCC is a United Nations organization that evaluates the science underlying climate change, potential risks, and possible approaches to adaptation and mitigation.

It was created in 1988 by the World Meteorological Organization and the United Nations Environment Program.

In 2022, 195 nations were members of the IPCC.

Reports of the Intergovernmental Panel on Climate Change

Bulletin of the American Meteorological Society: State of the Climate in 2021

U.S. Global Change Research Program: Fourth National Climate Assessment

ProPublica: New climate maps show a transformed United States

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