Carbon Dioxide (CO2)

Carbon dioxide (co2) is a chemical compound made up of one carbon atom and two oxygen atoms. While it is a trace gas in the atmosphere in terms of volume, it is of central interest to atmospheric chemistry due to its capacity to trap incoming solar radiation in the atmosphere. For this reason, it has become known as a greenhouse gas, where increases of carbon dioxide into the atmosphere cause climate changes, which include global warming. Other greenhouse gases include methane (CH4), nitrous oxide (N2O), tropospheric ozone (O3), halocarbons (CFCs, HFCs, HCFCs), and water vapor (H2Ov). Carbon dioxide is the principle greenhouse gas that contributes to climate change and global warming, as increases in carbon dioxide have contributed most to climate change compared to other greenhouse gases over time.

Carbon dioxide is part of larger carbon cycles on Earth. All living things are composed primarily of carbon, so the cycling of carbon through the various spheres can provide indications of the health of the planet. Unlike other greenhouse gases, carbon dioxide is not broken down or destroyed through chemical reactions. Aside from time spent in the atmosphere mainly as carbon dioxide, carbon also moves through the biosphere, hydrosphere and lithosphere. For example, atmospheric carbon dioxide is taken out of the atmosphere and up into the biosphere through photosynthesis. The carbon can then stay in this “reservoir” until the forest dies and decomposes, is cut down, or is burned. At this time, carbon is then released again to the atmosphere mainly as carbon dioxide.

There are many reasons why carbon dioxide is so influential in climate change. Among them, carbon dioxide has a long “residence time:” emissions can stay in the atmosphere for up to 200 years. For instance, emissions from a 1911 Model T Ford are potentially in the atmosphere today. This also means that even if all carbon dioxide emissions were halted today, declines in atmospheric carbon dioxide would only begin after the carbon dioxide cycled out of the atmosphere into another reservoir. Furthermore, carbon dioxide is the greenhouse gas most directly responsible for climate change by way of human activities (called anthropogenic climate change). This is also called the enhanced greenhouse effect. In the climate science community, there is overwhelming consensus that human activity has significantly driven climate changes in the past two centuries.

It is important to understand that there are also natural sources of carbon dioxide emissions. These include plant decomposition and volcanic activity, which contribute to a baseline natural greenhouse effect that makes the world habitable. Without them, the earth would on average be about 60 degrees F cooler and the planet would be covered with ice. With this natural greenhouse effect, humans have been able to live and enjoy benefits such as forest and food growth.

Looking more carefully at this distinction in sources of carbon dioxide emissions, climate research has shown that three quarters of atmospheric warming since 1850—the beginning of the Industrial Revolution—has been attributed to anthropogenic sources. These anthropogenic sources include fossil fuel burning (primarily coal, gas, and oil) and land use change. In the United States, roughly a quarter of anthropogenic climate changes can be attributed each to transportation, industry, household use/infrastructure, and land use and land-cover changes.

...