Understanding Carbon Footprint


If we are going to live a green life, we need to have a basic understanding of the idea of a carbon footprint. Here is a simple definition:

Carbon footprint is an attempt to estimate the total impact we have on global climate change when we buy or do something.

Let’s break that down to its components. First, carbon refers to the gases that are produced whenever we burn fossil fuels (coal, oil, natural gas). We’re using the term carbon to mean not just carbon, but all the greenhouse gases emitted by burning fossil fuels (methane, nitrous oxide, and refrigerant glasses). What is so bad about putting more carbon into the air? Life can exist on this planet in a very narrow range of temperature, too warm or too cold, and all life comes to an end. The temperature is regulated by the atmosphere around the earth, specifically by the greenhouse gases in the atmosphere: carbon, methane, AND nitrous oxide. When sunlight enters the atmosphere and hits the earth, some of the heat from the sun is reflected back into the atmosphere, where the greenhouse gases hold some of it. So, in a sense, carbon in the air acts like “insulation,” warming the atmosphere. (That’s the reason we call them “greenhouse” gases—they maintain a constant temperature in the greenhouse we call earth.) Somehow, for millions of years the earth has been self-regulating, as the heat from the sun increased, the gases warming the earth decreased. But in modern times, human activity is pouring carbon into the air at incredible rates. In 2007 the best estimate is that human activity poured 50 Billion Tons of carbon into the air. Of course that is an incomprehensible number, so let’s compare the human carbon footprint to earth’s natural footprint. Since there is a popular myth that a single volcano does more harm than all of human activity, we’ll start there. In the average year, all the volcanoes in the world produce 300 million tons of carbon (that is less than 1 percent of human activity and less than half of Australia’s output alone of 610 million tons). It is true that some of the enormous eruptions put out more carbon. The 1991 Mount Pinatuba eruption in the Philippines is estimated to have put 42 million tons into the air, but compare that to the United States carbon output of 8,250 million tons per year.

Another way the earth naturally produces carbon on a large scale is forest fires, so let’s look at them. No two years are the same for forest fires, but the best estimates of the 1997-1998 season is that it put out 2.1 billion tons. Again, that is only 4 percent compared to human activity, and roughly a quarter of the U.S. carbon footprint. Plus, if you have ever gone back to an area just a few years after a forest fire, it is amazingly green. All that new growth goes a long way toward reabsorbing the carbon put out by the forest fire.

Here is the bottom line, the more carbon in the air, the warmer the planet will get, and humans are putting huge amounts of carbon into the air, even compared to natural and geologic activity. The great majority of scientists think that we have already reached the point where human activity is increasing the average temperature of the globe. It’s a big, difficult topic, and I will leave you to make your own research and decision, but I think it is completely reasonable to say that living a low carbon footprint life is a very good thing.

There is one more thing we need to know about carbon footprints. There are two ways that burning fossil fuel puts carbon into the air: direct and indirect. Let’s look at burning 1 gallon of gas in a car. The direct way it produces carbon is obvious, the engine burns gas and carbon comes out the tailpipe. That is simple and easy to measure. But a whole lot of carbon was produced indirectly so we could burn that gallon of gas. First, the gas didn’t magically appear in the gas tank. The oil had to be pumped up out of the ground, transported to a refinery, refined and finally transported to the gas station where you bought it. That entire process is very dirty and produced a lot of carbon. Second, an even bigger indirect carbon footprint is the carbon footprint of the car itself. Again, it didn’t magically appear out of thin air, an enormous amount of fossil fuel was burned to manufacture that car. Here is an estimate of the carbon footprint of creating three sizes of cars:

  • Smart Car:  6 tons of carbon
  • Ford Taurus:  17 tons of carbon
  • Large SUV:  35 tons of carbon

Because it is fairly simple to determine the direct footprint of our activities and extremely difficult to determine the indirect carbon footprint, nearly all carbon calculators greatly underestimate the actual total carbon impact in their calculations.

It’s important to realize that carbon footprints are limited to examining global climate change and not necessarily the total environmental impact something may have. For example, generating power in a nuclear power plant has a very low carbon footprint because it is not burning fossil fuel and so isn’t contributing to global warming. But that doesn’t make it good for the environment. When considering its total environmental impact, we would also have to take into account the great danger from accidental release of radiation in an accident (Three Mile Island, Chernobyl, and Japan in 2011) and the insurmountable problem of storing spent fuel. Another example is generating hydro power from dams like the Hoover Dam in Nevada. It produces virtually no carbon and has very little impact on global climate change, but it consumes a huge amount of land with a negative impact, so the carbon footprint doesn’t tell the whole story. It isn’t enough just to look at carbon footprints when trying to live a green life.

Even with all its limitations and uncertainties, the concept of a carbon footprint remains one of our best tools to guide our new, green life. In one sense it is like money. We probably don’t know the exact cost of a bottle of champagne, but we are sure that it is more than a cup of coffee. I am equally certain that the cost of a house is a great deal more than either of those. We have a general sense of the cost of something. In the same way, I may not know the exact carbon cost of driving my car 3 blocks to a store down the street, I am pretty sure that it is higher than walking. I may not know the carbon footprint of a banana, but I’m certain that taking a flight from Seattle to Miami is much higher, and much more important to look for alternatives or ways to mitigate its impact. Because the concept of the carbon cost of something is new to us, you probably haven’t developed that sense of values yet.

A very good way to get started is to buy the book “How Bad Are Bananas?” by Mike Berners-Lee. In trying to learn about carbon footprints and global warming, I’ve read quite a few books and this was by far the best one I found. He does an outstanding job of giving not only specific details but a general sense of carbon footprints. Most of the information presented here is from his book. It is balanced, reasonable and humble. He presents lots of information in an understandable way. Best of all the science is accessible, understandable, and for the most part, not gibberish as is so often the case. If you are interested in the topic, this is a great book to start with.