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This backgrounder explains what greenhouse gases are and how they contribute to climate change.
How do greenhouse gases affect the Earth's atmosphere?
Did you know that the Earth is actually covered in a blanket? We call this blanket the atmosphere. Relative to the planet's size, this blanket is very thin. If the Earth were the size of an apple, the atmosphere would be the thickness of the skin of the apple. Though thin, the atmosphere is really good at keeping the planet warm. The average temperature on Earth is 15°C. But without the atmosphere, the average temperature on Earth would be a frozen -18°C. As you can imagine, not many things that live comfortably at 15°C could survive at -18°C.
The atmosphere keeps Earth warm through a phenomenon known as global warming. This happens due to greenhouse gases (GHGs). GHGs are gases with heat-trapping properties. They are found in the Earth’s atmosphere. When the sun's rays strike the Earth, the Earth’s surface is heated. This heat rises and radiates away from the surface.
What are the main greenhouse gases?
carbon dioxide (CO2)
nitrous oxide (N2O)
sulphur hexafluoride (SF6)
Water vapour, although not on the UN list, is also technically a greenhouse gas.
Not all of these gases are equally good at trapping heat. For example, methane is 25 times better at trapping heat than carbon dioxide. We call this its Global Warming Potential (GWP). One tonne of methane (CH4) captures as much heat as (or is equivalent to) 25 tonnes of CO2. To make comparing gases easier, we convert them all into CO2 equivalents (CO2e).
Global Warming Potentials of Various Gases
Carbon dioxide GWP = 1
Methane GWP = 25
Nitrous oxide GWP = 298
HFCs, PFCs, SFs GWP = 12 422 800
Burning fossil fuels is the main source of CO2. There are many human activities that produce CO2. For example, the combustion of gasoline and Diesel fuel in vehicles produces CO2. The combustion of coal and natural gas in electricity-generating power plants produces CO2. Various industrial processes produce CO2 too. Plants remove, or sequester, CO2 from the atmosphere during photosynthesis.
One of the most important sources of methane is the production and transportation of natural gas, oil, and coal. The digestive processes and waste products of domestic livestock release methane, too. Landfills also release methane. This happens as waste decomposes.
Fuel combustion in motor vehicles is the primary source of N2O. Agricultural activities also contribute nitrous oxide to the atmosphere. One example is adding nitrogen from synthetic fertilizers to soil.
HFCs, PFCs, SFs
These GHGs do not have very high concentrations in the atmosphere. However, they have incredibly high GWPs. These high GWPs mean they can have an important warming effect on the Earth. All three types of gases are synthetic, which means that they do not occur naturally in the environment. Instead, they are produced as a result of various industrial processes. For example, they are produced during electricity transmission. They are also produced by air conditioning systems.
GHGs prevent some of the heat (infrared radiation) from escaping back out to space. This is called the greenhouse effect. Today, human activities are pumping way too many GHGs into the atmosphere. As a result, the blanket is, in a sense, getting thicker. It’s making the planet hotter and the weather more extreme. The effect humans have on the atmosphere is called the anthropogenic greenhouse effect. Before the Industrial Revolution, the concentration of carbon dioxide (CO2) in the atmosphere was 280 parts per million by volume (ppmv). Today, it is at 405 ppmv. This is higher than it has been in over 800 000 years. And that number is continuing to go up.
Scientists believe this excessive concentration of GHGs is the cause of climate change. By 2005, the Earth was about 0.75 degrees warmer than in 1906. This may not sound like that much. But scientists agree that we must not exceed more than a 2°C rise in average global temperatures. Otherwise, we may face catastrophic impacts from climate change.
Some of these catastrophic impacts include:
A loss of sea ice
A rise in sea levels
More intense and longer-lasting heat waves
More frequent extreme weather events, like hurricanes and tornadoes
Each of these impacts has rippling consequences. For example, if there are more frequent extreme weather events, there may also be more deaths and injuries caused by these events. Rising temperatures can lead to more high-temperature days. This can put people at a higher risk for heat-related illnesses and dehydration.
Also, if climate patterns change, the distribution of insects might change, too. That’s a problem for many reasons, including that insects can carry fatal diseases.