Carbon dioxide has been a driver of the world’s climate for millions of years. It is a greenhouse gas that absorbs heat radiated from Earth rather than letting the heat escape into space. So, carbon dioxide in the atmosphere helps to warm the Earth to a comfortable temperature.

A problem arises when too much carbon dioxide is in the atmosphere. The Earth gets warmer than we want. We cannot blame this on Mother Nature. Left to nature there would be just the right amount of carbon dioxide in the atmosphere. The real culprit is us. Through our activities the amount of carbon dioxide in the atmosphere has expanded, causing the Earth’s temperature to rise and the climate to change.

Carbon dioxide is the most prevalent long-lived greenhouse gas. Emissions come from decomposed plants and animals stored deep in the earth. The carbon is brought to the Earth’s surface where it is emitted into the atmosphere through the process of burning. The carbon can be in a solid form (coal), liquid form (crude oil), or gaseous form (natural gas).

While the pre-industrial atmospheric carbon dioxide concentration was about 280 parts per million, or ppm, current measurements show the concentration is above 400 ppm. The atmosphere now contains more carbon dioxide than at any time in the last 420,000 years and possibly the last 20 million years. With strong economic growth and no limits on carbon dioxide emissions, scientists predict atmospheric concentration could reach 600 ppm by 2050. In addition, once carbon dioxide is emitted, it stays in the atmosphere for centuries.

Atmospheric carbon dioxide has an important natural cycle that is critical for plant life on earth. Crops, trees and the flowers in your back yard use the process of photosynthesis to grow and flourish. Photosynthesis takes carbon dioxide from the air and uses it to build the plant. When the plants die and decompose, the carbon dioxide is released back into the atmosphere.

So, the flowers in your back yard take carbon dioxide out of the air in the spring and summer when they grow and release it back into the atmosphere when they die in the fall. But this annual fluctuation should not be confused with the long-term upward trend in atmospheric carbon dioxide over many years.

The earth’s carbon-cycling biosphere was in balance with the atmospheric carbon dioxide before humans began releasing massive amounts by burning fossil fuels. The global biosphere is unable to take up this rapid increase. For example, each Iowan contributes about 30 tons of carbon dioxide to the atmosphere each year, which would require growth to maturity of several trees each year to avoid adding carbon dioxide to the atmosphere.

Don Hofstrand is a retired agricultural economist from Iowa State University Extension. During the last few years of his work life, he focused on renewable energy and climate change. He and his wife live in Mason City.

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