Atmospheric Carbon Dioxide: History & Environmental Effects

Instructor: Sheila Morrissey

Sheila has a master's degree in geology and has taught middle school through university-level science courses.

After this lesson about atmospheric carbon dioxide, you will be able to describe how carbon dioxide levels in our atmosphere have changed over time due to both natural transitions and human-caused disturbances.

Carbon Dioxide and the Greenhouse Effect

Carbon dioxide is a naturally occurring gas found in Earth's atmosphere. As one of the greenhouse gases in our atmosphere, carbon dioxide helps keep Earth at a warm, livable temperature. Without greenhouses gases, we would freeze. Molecules of greenhouses gases, like carbon dioxide, are capable of briefly storing energy of a particular wavelength and re-emitting that same energy again. The sun is intensely hot, and therefore emits short-wavelength energy that we see as light. Some of the sun's emitted energy is absorbed by the Earth, which emits its own shorter-wavelength energy, infrared radiation. It's this infrared radiation that can be held in greenhouse gas molecules. As that energy is released again, it can go in any direction. The energy can be sent back out of our atmosphere, sent to another greenhouse gas molecule, or sent back toward the Earth's surface. The greenhouse gases keep some of Earth's emitted infrared energy trapped in our atmosphere. It is this trapping of energy and its similarity to agricultural greenhouses that gives greenhouse gases their name. Since the Industrial Revolution, the burning of fossil fuels has added to Earth's atmospheric carbon dioxide levels, increasing the greenhouse effect and leading to higher temperatures on Earth.

The Greenhouse Effect
Greenhouse Gases

Natural Changes in Atmospheric Carbon Dioxide

The Earth cycles through glacial and interglacial (between glacial) periods that are initiated by slight differences in Earth's orbit as the gravitational pull from other planets changes. When Earth receives more light energy from the sun, the planet warms up, releasing dissolved gases from the ocean. Consider an open bottle of soda. You'd put it in the refrigerator to keep it from going flat, right? That's because colder water can hold more dissolved gases. Allowing your soda to warm to room temperature allows the dissolved carbon dioxide to escape. Similarly, warming the ocean allows dissolved carbon dioxide to escape. Increased energy reaching the Earth from the sun increases the Earth's temperature, and adding in more greenhouses gases to our atmosphere works to increase that temperature even more by the greenhouse effect. The rise and fall of atmospheric carbon dioxide therefore coincides with changes in temperature on Earth. During interglacial warm periods, the Earth's average temperature has been about 5 degrees C warmer than during glacial periods.

Atmospheric carbon dioxide levels over time in thousands of years (kya). The data in blue are from the Vostok ice core, and the data in red are from ice cores in Law Dome and from direct measurements in Mauna Loa.

Anthropogenic Carbon Dioxide

Since the Industrial Revolution, there has been a continuously increasing use of fossil fuels. The burning of fossil fuels results in the formation of carbon dioxide and increases the carbon dioxide content in our atmosphere. Data capturing the rise in atmospheric carbon dioxide was notably recorded by a scientist named Charles David Keeling. His measurements and the more recent atmospheric data added from his sampling site at Mauna Loa are known as the Keeling Curve. The seasonal cycles seen on the Keeling Curve indicate the growing cycles of photosynthesizing plants in the Northern Hemisphere, where there is more land mass for plants than in the Southern Hemisphere. The overall increasing trend in atmospheric carbon dioxide is due to rise in anthropogenic (human-caused) sources of carbon dioxide.

The Keeling Curve demonstrates rising atmospheric carbon dioxide measured since 1958
Keeling Curve

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