Carbon Dioxide -The Gas That Feeds Us And Could Kill Us!
DR. DENNIS B. EGLI
LEXINGTON, KENTUCKY
Carbon dioxide (CO2) currently makes up about 0.042% (420 ppm) of the atmosphere - a minuscule concentration in comparison with oxygen (21%) or nitrogen (78%) - but it is the key to all life on earth. Carbon dioxide is the source of all of the food that sustains us, while, on the other hand, this gas is widely reviled as a greenhouse gas that is causing climate change that could eventually kill us. Ironically, it is also the source of all of the fossil fuels (coal, petroleum and natural gas) we have been burning for the last several centuries. A classic case of the good, the bad, and the ugly wrapped up in a single gas. Let’s untangle this complicated situation, starting with the ‘good’ – its role in providing our food.
Carbon dioxide in the atmosphere is the source of our entire food supply. Plants use energy from the sun to convert CO2 into simple sugars via photosynthesis. Plants can transform these simple sugars into complex carbohydrates, protein (with N), fats and oils that make up the food we eat. Some of these plant products are fed to animals to provide us with meat, milk and eggs.
Of course, food production requires other inputs (N,P, K, micronutrients, water) and favorable temperatures, but C from CO2 is the fundamental ingredient. We couldn’t have our morning coffee or a hamburger for lunch (along with the beer to wash it down) if it wasn’t for the CO2 in the atmosphere.
The ‘bad’ face of CO2 is its role as a greenhouse gas that causes climate change. Radiation from the sun warms the earth’s surface which cools by emitting long-wave radiation that we can’t see. Greenhouse gases (CO2, methane, nitrous oxide and water vapor) in the atmosphere absorb some of this long-wave radiation and reradiate back to the earth’s surface, reducing the amount of cooling. The greenhouse gases essentially act like a blanket thrown over the earth. The thicker the blanket, (the higher the greenhouse gas concentrations) the warmer the earth.
The term ‘greenhouse’ is used because these gases act just like the glass on a greenhouse. The glass lets solar radiation pass through, but it absorbs the long-wavelength radiation from the benches and plants in the greenhouse, so the greenhouse gets hot, just like the earth.
Scientists first realized that CO2 was a greenhouse gas in the early to mid- 1800s. At that time, some of them predicted that continuing to put CO2 into the atmosphere by burning fossil fuels (mostly coal then) would eventually increase temperatures.
Atmospheric CO2 concentrations in 1800 were about 280 ppm, but burning coal and petroleum products has increased it to around 420 ppm today – concentrations the earth hasn’t seem for 3 million years.
While we worry a lot about the effects of the enhanced greenhouse effect and climate change, the truth is we depend upon CO2 in the atmosphere to make the world habitable. The earth would be too cold to support life if there were no greenhouse gases in the atmosphere. Life on earth depends on that blanket, but it can’t get too thick. A classic exception to the old saying – if a little is good, more is better.
Ironically, the root cause of our problems with global warming traces back to the photosynthetic fixation of carbon that also feeds us. The fossil fuels that are increasing the CO2 in the atmosphere originated from photosynthesis and plant growth. Plant remains were buried under sediments and over millions of years were turned into coal and petroleum. The energy in coal and petroleum came, originally, from photosynthesis and CO2 in the atmosphere. Now we are returning it to the atmosphere where it is causing climate change. This might seem like harmless recycling but deposits that accumulated over millions of years are being turned into CO2 in just a few years and atmospheric concentrations are going up.
The story of CO2 is a story with many twists and turns. We have known for more than 200 years that increasing the CO2 concentration in the atmosphere would warm the earth and now we are starting to see the effects – not just higher temperatures, but droughts (and the fires that come with them), floods and an increase in severe storms. On the other hand, greenhouse gases make the earth habitable, and CO2 feeds us. Talk about a dual personality - the gas that feeds us may also end up killing us if we don’t eliminate our use of fossil fuels.
“We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature’s inexhaustible sources of energy – sun, wind and tides. … I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait until oil and coal run out before we tackle that” (Thomas Edison, inventor, 1847 – 1931). ∆
DR. DENNIS B. EGLI: University of Kentucky