“Carbon dioxide is a greenhouse gas.” We hear that all the time. But what does it actually mean? To start, carbon dioxide is a gas consisting of two oxygen atoms combined with one carbon atom. It is produced as part of the respiratory system in animals (we exhale it), and as a byproduct of burning fossil fuels.
Why is it called a greenhouse gas? Well, if you take out your handy periodic table (don’t we all carry one in our purse or wallet?), you’ll see that carbon is right above silicon, which means that they have very similar chemical properties. Silicon dioxide is the formula for quartz, which is the basic material in glass and, therefore, greenhouses. Thus, the carbon dioxide in the atmosphere behaves in a very similar way to the silicon dioxide in a greenhouse.
Sunlight delivers heat to a greenhouse – or the Earth – in the form of visible light, mostly in the yellow part of the spectrum. This is a high-frequency, short-wavelength form of radiation that can easily pass through silicon dioxide and carbon dioxide molecules. At night, the greenhouse – or Earth – will try to reradiate that heat back to space, but as much lower-frequency, longer-wavelength infrared radiation. This longer wavelength is too large to pass through the silicon dioxide or carbon dioxide, and thus gets trapped, allowing the greenhouse or Earth to stay warm. Graphs of carbon dioxide levels and temperature show a close correlation, as predicted by this analysis.
Carbon dioxide is not the only greenhouse gas. Carbon monoxide, methane and water vapor are others, but it is among the most prevalent. Just last month, it was reported that carbon dioxide levels reached 415 parts per million for the first time in human history. To put that in perspective, carbon dioxide levels naturally ranged between 180 ppm during glacial periods (ice ages) and 270 ppm during inter-glacial times – a variation of 90 ppm over tens of thousands of years. Since the beginning of the Industrial Revolution, when we began powering our machines by burning fossil fuels, those levels have risen from 270 ppm to the 415 ppm we’ve just recorded – an increase of over 140 ppm in about 150 years.
The fear among climate scientists is that these high levels of carbon dioxide will lead to increased warming of the atmosphere, which will lead to potentially dramatic changes in our weather patterns, bringing instability to our ecosystems and ultimately to our economic systems as well. And the problem gets worse – increased heat from increasing carbon dioxide levels will lead to positive feedback loops – increased melting of the icecaps, which reflect sunlight, and evaporation of the oceans, causing them to release more of the carbon dioxide that they store, will drive the system to the point where we can’t fix it.
The solution is to reduce the carbon dioxide in our atmosphere by cutting our emissions of carbon dioxide by burning less fossil fuel, and/or figuring out ways to sequester carbon dioxide in the ground. These are not quick and easy solutions. If they were, we’d have done them already. This is a challenge we must undertake – not for ourselves, necessarily, but certainly for our children and grandchildren and the generations to come.
• Paul Stoddard is a professor emeritus of Geology and Environmental Geosciences at Northern Illinois University.