Global Gas Emissions

Common sources of Federal greenhouse gasesFigure 1: Scope 1, 2, and 3 emission types form the Cool Climate Network

Main Emission Types

Carbon Dioxide (CO2)

A naturally occurring gas that enters the atmosphere through the burning of fossil fuels, such as coal, natural gas, and oil. It can also enter the atmosphere through burning solid waste, trees and wood products, or as a byproduct of certain chemical reactions. Therefore, deforestation is a large factor in increasing emissions. Conversely, reforestation and soil improvement help CO2 leave the atmosphere (or be “sequestered”) as it is used in the biological carbon cycle. The carbon cycle consists of animal and plant respiration, volcanic eruptions, and ocean-atmosphere exchange. Presently, CO2 accounts for 84% of US and 77% of global gas emissions.

Nitrous Oxide (N2O)

Currently makes up 5% of US and 8% of global gas emissions. It results from the burning of solid waste and fossil fuels, including coal, natural gas, and oil. The production of fertilizer and soil cultivation in agricultural and industrial activities yields N2O.

Methane (CH4)

Arises from agricultural practices, especially those dealing with livestock. It is also produced with the decay of organic waste, particularly in solid waste landfills. Lastly, CH4 is emitted with the manufacture and transport of energy (coal, natural gas, and oil). It accounts for 9% of US and 14% of global gas emissions.

Fluorinated gases (F-gases)

These gases are synthetic, or human-made, and are emitted from industrial activities and refrigeration. Although they are emitted in small amounts (2% in the US and 1% globally), they are powerful greenhouse gases and are referred to by some as Global Warming Potential gases or “High GWP gases”.

  • Hydrofluorocarbons (HFCs): mostly used in refrigeration and insulation.
  • Perfluorocarbons (PFCs): produced by aluminum smelting and used in manufacturing semiconductors.
  • Sulfur hexafluoride (SF6): produced in heavy industry for insulation and for the manufacture of cable cooling systems. 

pie chart of emissions gasesFigure 2: U.S. Greenhouse Gas Emissions in 2011 from the EPA

pie chart of emissions gasesFigure 3: Global Greenhouse Gas Emissions by Gas from EPA and IPCC (2007)

Other Emission Types

Water Vapor 

The most important and copious greenhouse gas. It has a short lifespan in the atmosphere and is not as directly influenced by human activities as the above emissions. Globally, water vapor is most regulated by temperature, which effects evaporation and precipitation.

Tropospheric ozone (O3)

Is naturally occurring but can also be a potent pollutant resulting for human-made conditions. It lasts a short time in the atmosphere. O3 is created by chemical reactions between N2O emissions and volatile organic gases from industrial and commercial sources in sunlight, such as automobiles and power plants. Not only does it trap heat in the atmosphere, it also damages respiratory health, crops, and the global ecosystems. At its highest atmospheric levels, though, it protects the earth from ultra-violet radiation and chemicals that may damage or eliminate ozone.

Non-Gas Climate Forcers

Black Carbon

An aerosol (solid particle) that also increases atmospheric temperature. Unlike the above gases, it can directly take in incoming and reflected sunlight as well as infrared radiation. Moreover, it can deposit onto and obscure snow and ice. This increases the absorption of sunlight by the snow and increases its melting rate.

Sulfates, organic carbon, and other aerosols

Capable of reflecting sunlight and, thereby, contribute to cooling.

Warming and cooling aerosols

Can change cloud characteristics (formation, dissipation, reflectivity, and precipitation rates) through direct interaction. This then effects cooling and warming as the clouds either reflect or trap outgoing heat.


J. Alyssa White

Last Updated: October 10, 2016