If you've been following the global warming discussion at all, you probably know that scientists believe that car exhaust pipes and power plant stacks are pumping too much carbon dioxide into the atmosphere. That, in turn, increases the Earth's natural greenhouse effect, in which heat from the sun's rays is trapped in the atmosphere instead of radiating back into space.
People who don't believe that humans are causing the planet to heat up sometimes point out that even though we're spewing out more carbon dioxide than ever before, the gas still only amounts to a minute fraction of Earth's atmosphere — just 0.04 percent, to be precise [source: Gillis] . How could such a small portion of the atmosphere cause so much harm?
Focusing upon the relative concentration is like claiming that a tiny quantity of arsenic or cobra venom couldn't possibly kill you [source: Gillis]. And carbon dioxide is really good at trapping heat. While the gas only amounts to not even half of a percent of the atmosphere, it accounts for 20 percent of the greenhouse effect [source: NASA]. So increasing that tiny bit of atmospheric CO2 can have a disproportionately huge effect.