This page is a resource for understanding greenhouse gases, climate change and the challenge of stabilizing the climate.
Climate Change And Greenhouse Gases
Shrink That Footprint is about carbon reduction. Let’s understand what that means in more detail. Climate scientists have long warned that greenhouse gases released by human activity are trapping heat and causing the Earth’s climate to change. Over the past century, the Earth’s average surface temperature has risen by about 1.5 degrees Fahrenheit (0.8 degrees Celsius), and most of that warming has occurred since the 1970s, according to the National Oceanic and Atmospheric Administration.
The United Nations’ Intergovernmental Panel on Climate Change has concluded that it is “extremely likely” that more than half of the global warming since the 1950s has been caused by human emissions of greenhouse gases. This year at the COP27 in Egypt, the convened international group agreed that the future increase of 1.5 degrees Celsius is all but unavoidable. Yet, we have a very narrow window to avert the 2.0 degree Celsius increase.
Common Greenhouse Gases
These gases, which include carbon dioxide, methane and water vapor, act like a blanket around Earth, trapping heat and causing the planet’s average temperature to rise. As the world has warmed, scientists have documented a number of changes, including rising sea levels, shrinking snow cover, retreating glaciers and melting Arctic sea ice. They have also linked climate change to an increase in extreme weather events, such as heat waves, droughts, wildfires and floods.
Carbon Dioxide – carbon dioxide is the primary greenhouse gas responsible for human-caused climate change. It is produced when we burn fossil fuels, like natural gas, oil, and coal. Burning these materials release carbon dioxide into the atmosphere. Carbon dioxide comprises 79% of greenhouse gas emissions in the US.
Methane – methane is a powerful greenhouse gas that is produced both naturally and as a result of human activity. It is produced when organic matter decomposes in the absence of oxygen, like in landfills and wetlands. It is also emitted during the production and transport of coal, natural gas, and oil. Methane makes up 11% of greenhouse gas emissions in the US. Interestingly, even though its 8 times less by emissions weight, methane is a more potent greenhouse gas.
Nitrous Oxide – nitrous oxide is a greenhouse gas that is produced both naturally and as a result of human activity. It is emitted when nitrogen-containing fertilizers are used, and it is also a byproduct of burning fossil fuels. Nitrous oxide makes up 7% of greenhouse gas emissions in the US.
Fluorinated Gases – fluorinated gases are man-made chemicals that have a very high global warming potential. They are used in a variety of industrial and commercial applications, such as refrigeration and air conditioning. Fluorinated gases comprise 3% of greenhouse gases in the US.
In 2018, the United Nations’ Intergovernmental Panel on Climate Change issued a report that warned of catastrophic consequences if the world does not take action to cut emissions of greenhouse.
Potential To Warm The Earth For Each Gas
The potential for each gas, given a specified time, to warm the earth, is given by a unit called the “Global Warming Potential” (GWP). And to make things really easy, scientists scaled the unit so that carbon dioxide, the most common greenhouse gas, has a GWP of 1.
Methane, another important greenhouse gas, has a GWP of 25, which means that it can trap 25 times more heat than an equivalent amount of carbon dioxide over the same time. Nitrous oxide, another greenhouse gas, has a GWP of 298. Chlorofluorocarbons, or CFCs, are a group of man-made chemicals that were once used in refrigerators, air conditioners and other consumer products. They were successfully phased out in the 1980s by the entire world because they were found to be damaging the Earth’s ozone layer. The elimination of CFCs as a component of refrigerant gases represents a great example of global success.
CFCs have a GWP of up to 20,000, which makes them one of the most potent greenhouse gases. Hydrofluorocarbons, or HFCs, are a group of man-made chemicals that are used as substitutes for CFCs. They do not damage the ozone layer, but they are potent greenhouse gases. HFCs have a GWP of up to 4,000.
The Montreal Protocol, which was signed in 1987, is an international treaty designed to protect the Earth’s ozone layer by phasing out the production of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and other ozone-depleting chemicals. The Protocol has been successful in dramatically reducing the production and consumption of CFCs and HCFCs, and as a result, the ozone hole has begun to heal. Scientists expect the ozone layer to return to its pre-1980 levels sometime in the middle of this century. As a consequence, the elimination of CFCs in refrigerators means less potent greenhouse gas as well.
Computing The Total Impact
It’s not enough to just call out gases with high GWP. A gas with high GWP might break down or escape from the atmosphere, in which case its impact is limited by its life time. Therefore, the concept of a gas’s lifetime in the atmosphere is important too.
Moreover, not all gases are emitted equally. Therefore, as a contributor to increased warming, one needs to take into account the total amount of emitted. The total impact, in a simplified way, would be to combine the GWP, the time in atmosphere, and the fraction emitted annually of that gas. The following table summarizes these ideas.
Summary Of GWP
| Greenhouse Gas | Global Warming Potential (GWP; given as multiple of CO2 GWP) | Time in atmosphere (years) | Percent of emitted |
| Carbon Dioxide (CO2) | 1 | 300 | 72.6% |
| Methane | 25 | 12 | 10.9% |
| Nitrous Oxide | 298 | 109 | 7.1% |
| Chlorofluorocarbons (CFCs) | 20,000 | 52 | – |
| Hydrofluorocarbons (HFCs) | 4,000 | 222 | – |
Source for percent emitted is from EIA.gov
Source for GWP and time in atmosphere is from GWP in Wikipedia.
