We hear a lot about carbon dioxide when we talk about climate change, but sometimes it's important to go back and examine why too much CO2 in the atmosphere is a bad thing.

CO2 — a naturally occurring gas that is also emitted at great levels by human activity — is one of several greenhouse gases in our atmosphere. Other greenhouse gases include water vapor, methane, ozone, nitrous oxide and halocarbons. To understand the impact of these gases, we first start with the sun, which sends solar radiation in the form of light to Earth. The atmosphere deflects some of this radiation, while the rest hits the planetary surface and warms the land and oceans. The Earth then radiates its own heat back up in the form of infrared rays. Some of those rays escape the atmosphere, while others are absorbed and then re-emitted by the atmospheric gases. These gases – the greenhouses gases – then help to keep the planet at its normal temperature.

For millions of years, the production of greenhouses gases was regulated by the natural systems of the planet. Gases would be absorbed and emitted at a fairly steady rate. Temperatures, meanwhile, were maintained at a level that supported life around the world. The Environmental Protection Agency characterizes this as "a balancing act."

Humans changed the balancing act beginning in the second half of the 1700s, at the start of the Industrial Revolution. Since that time we have been adding greenhouse gases, primarily CO2, to the atmosphere at a steadily increasing rate, trapping that heat and warming the planet. Although there are several greenhouse gases — some are more potent than others — CO2 currently represents about 84 percent of all greenhouse gases emitted by human activities, totaling about 30 billion tons a year. Most of this comes from burning fossil fuels for electricity and transportation, although industrial processes and forestry also contribute heavily.

Before the Industrial Revolution, CO2 levels were about 270 parts per million (ppm). CO2 levels were at about 313 ppm in 1960. They reached 400 ppm earlier this year. Many climate scientists say levels need to be reduced to 350 ppm to avoid the effects of climate change.

Carbon dioxide graphic

Source: NOAA

Carbon dioxide isn't only affecting the atmosphere. It has also made the oceans about 30 percent more acidic, affecting a wide variety of sea organisms. That percentage is also expected to rise in the coming years.

Obviously all of this carbon we have added to the atmosphere will not go away overnight. Its effects will be destructive and long-felt. But by understanding the impact of CO2, hopefully we can make steps toward reducing our emissions and, if we're really lucky, avoid the worse effects of climate change yet to come.

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