Chris Averill

Last week, the Obama Administration announced plans for new regulations designed to limit methane emissions in the oil and gas sector where large amounts of methane are often emitted during production. The goal of these new rules is to cut methane emissions from oil and gas production 45 percent by 2025. Methane is the second most abundant greenhouse gas in the atmosphere, after carbon dioxide. Methane’s potential to cause climate change is at least 20 times higher than carbon dioxide, over a span of 100 years.

Not all gases contribute to climate change equally. By understanding how different gases behave in the atmosphere, one can better grasp why methane has such a large impact on climate change and why the administration is taking action to curb methane emissions

Several different measures are used to quantify climate change impact, including CO2 equivalents, Global Warming Potential (GWP), and Radiative Forcing. While the specific details used to calculate these vary, they are based on a common set of principles: the ability of a gas to absorb specific types of energy, the type of energy the gas absorbs relative to other gases in the atmosphere, and the lifetime of the gas in the atmosphere.

  • Ability to absorb infrared light: Every molecule absorbs energy. For gases in the atmosphere, this energy is mostly from sunlight, which contains visible light that our eyes can see as well as ultraviolet and infrared light. The Earth warms by absorbing some, but not all, of this light, and cool by giving off energy in the form of infrared radiation. Before all this radiation can escape the atmosphere, some of it is absorbed by greenhouse gases, which causes the atmosphere to warm. Methane, the second-most abundant greenhouse gas, absorbs significant amounts of infrared light.
  • Wavelength of light absorbed: Gases are also competing for infrared light. Water vapor is currently the only greenhouse gas that can trap infrared light and not contribute to climate change. It absorbs most of the infrared light that makes it to the Earth from the sun, which only leaves specific wavelengths of infrared light available to other gases. Only gases that are able to absorb what infrared light is left over will contribute significantly to climate change. Methane can absorb the infrared light that water vapor leaves behind, which contributes to its higher climate change potential.

    These are absorption spectra for water and carbon dioxide. The large white areas show wavelengths where water does not absorb and are  wavelengths where greenhouse gases could have a larger potential.

    These are absorption spectra for water and carbon dioxide. The large white areas show wavelengths where water does not absorb and are wavelengths where greenhouse gases could have a larger potential. NASA.

  • Lifetime of gas in atmosphere: The atmosphere has a variety of molecules that interact with each other in different ways. Some molecules break down more easily when they come in contact with other chemicals in the atmosphere. Other molecules break down incredibly slowly in comparison, which gives them a long lifetime. The longer a gas lasts, the more it contributes to climate change. Methane breaks down relatively quickly in the atmosphere, which decreases its climate change potential. Even though the lifetime of methane is short, it still has a great impact on climate change due to how it absorbs infrared light.

Climate change potential is based on these broad concepts, but understanding how different greenhouse gases contribute to climate change can provide the knowledge needed to identify emissions that need to be reduced. Based on methane’s potential to contribute to climate change it makes sense that the administration was motivated to take action to decrease its emissions.

Keywords: Energy