Greenhouse Gases

ACS Climate Science Toolkit

“Is the mean temperature of the ground in any way influenced by the presence of heat- absorbing gases in the atmosphere?”
—Svante Arrhenius, 1896

Source: Figure 1, FAQ 1.3, IPCC Fourth Assessment Report (2007), Chapter 1

What are “greenhouse gases?” The transparent windows of a greenhouse (or a car parked in the sunlight) transmit the warming visible rays of the sun, prevent the resulting warm air from leaving, and hence maintain a warmer environment inside than outside the structure. In the Earth’s atmosphere, some trace gases absorb infrared radiation from the solar-warmed surface of the planet and transfer energy to the many other surrounding molecules. The result is Earth’s temperatures higher than they would be in the absence of these gases. The atmospheric gases and a greenhouse work in quite different ways, but the resulting effect, higher temperature in both cases, has led to the nomenclature “greenhouse gases” for the atmospheric gases responsible for the atmospheric warming effect. Although this nomenclature is misleading, it is in such common use that we use it here as well.

Swedish chemist and 1903 Nobel Laureate Svante Arrhenius focused on this topic, posing it as the first question in his landmark 1896 paper. The paper sparked controversy at the time, but was later recognized as a pioneering contribution to the science of climate change as the first published research to attempt to quantify carbon dioxide’s (CO2’s) role as a greenhouse gas.

Now, over a century later, the mention of greenhouse gas usually evokes thoughts of carbon dioxide (CO2). That’s mainly because changes in the amount of CO2 in the atmosphere have been linked to the warming of the atmosphere over this past century. CO2 is an important greenhouse gas, and along with water vapor, keeps the Earth warm enough to support life as we know it. But there are many other gases (as well as substances like aerosol particles) that have roles in atmospheric warming and some of them have been emitted into our atmosphere largely as a result of human activity. They include methane, nitrous oxide, ozone, and halogenated gases. Some of these gases make significant contributions to changing the radiation balance of our planet.

Other important information for understanding the role of greenhouse gases in climate science:

Aerosol Particulate Matter —extremely small particles or liquid droplets, about 0.01 to 100 μm in diameter, suspended in the atmosphere —can also affect energy absorption/emission in the atmosphere. Lightly-colored aerosol particles can reflect incoming sunlight. Dark particles can absorb energy. Natural aerosol particles, usually larger than about 1 μm, include dust and sea salt whipped into the atmosphere by strong winds and particles from volcanic eruptions. Human-made aerosol particles, usually smaller than about 1 μm, include sulfate particles produced from sulfur dioxide (SO2) emitted by coal combustion and soot-like “black” carbon particles from wood-burning cook stoves – widely used in developing countries – and diesel engine exhaust. Aerosol particles also enhance cloud formation and so also exert an effect through the reflectivity and energy absorbing properties of clouds.