Greenhouse Gases

What Are Greenhouse Gases?

Gases that absorb and trap heat in the atmosphere are called “greenhouse gases.” As the amount of greenhouse gases in our atmosphere increases, the amount of heat trapped by the atmosphere also increases, causing the overall warming of the planet. This warming is referred to as global warming. The various impacts from global warming are referred to as climate change.

The major greenhouse gases include ozone, carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons. They come from both natural processes as well as human activities, though increases in the human-made greenhouse gases are most responsible for disrupting the balance of the atmosphere.

Greenhouse Gases in Our Region

In our region, nearly 50% of our greenhouse gas pollution comes from transportation – cars, trucks, trains, ships, etc. To help our region do its part and more to protect the climate, we are focusing our efforts on reducing pollution from the transportation sector.

The following are the major greenhouse gases in our region:

  • Carbon dioxide (CO2): Carbon dioxide enters te atmosphere through burning fossil fuels (coal, natural gas and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement).
  • Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, and sulfur  hexafluoride are synthetic, powerful greenhouse gases that are emitted  from a variety of industrial processes. Fluorinated gases are sometimes  used as substitutes for stratospheric ozone-depleting substances (e.g.,  chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases  are typically emitted in smaller quantities, but because they are potent  greenhouse gases, their release into the air is also important.
  • Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.
  • Nitrous oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.


In February 2017, the Puget Sound Clean Air Agency (Agency) Board adopted economy-wide greenhouse gas (GHG) emission targets of 50% below 1990 levels by 2030, and 80% below 1990 levels by 2050. These targets are based on the most recent scientific findings on the need to achieve significant emissions reductions to minimize the devastating impacts of climate change.

Since almost half of all GHG emissions in our region are from the transportation and mobile sector, the Agency’s Board of Directors directed staff to identify and evaluate potential candidate actions that could achieve significant reductions in transportation-related GHG emissions. This report provides a summary of those candidate actions.

To achieve the necessary emission reductions according to the Agency’s targets, staff recommends implementing candidate actions in the following three focus areas.

  • Zero-emission vehicle adoption
  • Promote alternative fuel use
  • Influence and increase mode-shift

While we developed the proposed candidate action and GHG emission reduction estimates with the best available information, there are still factors we cannot identify with certainty. What we are certain of is that GHG emissions are directly related to a changing climate that impacts our region, our air quality, and our vulnerable populations. These negative impacts will grow and worsen without actions to reduce our GHG emissions and improve our environment. As our strategic plan guides us, we must help our region “do its part and more to protect our climate.” Success will be challenging, but failing to defend the future is not an option.

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