Why Even Small Carbon Footprints Matter

Hey Mr. Green,
I've heard that humans account for only 3 percent of global carbon emissions, with the rest coming from volcanoes, forest fires, and plant decay. Is this true, and if so, how can reducing our carbon footprint make an appreciable difference to the global situation? –Cary in Atlanta, Georgia

Hey Cary,
Three percent may not sound like much, but if that small percent isn't reabsorbed each year, it keeps accumulating until you have a much bigger percent and a real problem. Think of it this way: If you only gain 3 percent in weight a year, it's not much. But if you never shed that weight, you'll balloon from a 135-pound lightweight-boxer to a full-size heavyweight (albeit a rather flabby one) in 20 years.

The natural world is estimated to emit a grand total of 770.3 billion tons of CO₂ annually. Millions of life forms on land, from bacteria to elephants, pump out 440 billion tons of CO₂, while the oceans release another 330 billion tons, and volcanoes add 300 million each year. Human activity, primarily from burning fossil fuel, but also from agriculture and forest burning and clearing, accounts for "only" 32.3 billion tons, New Scientist reports.