PhysOrg: Each year, between the burning of fossil fuels and the clearing of old growth forests, humans put about 10 petagrams of carbon dioxide (CO2) into the atmosphere. A petagram is one quadrillion grams. Ten petagrams is equivalent to the mass of Halley's comet, to put it in perspective.
Having a steady amount of CO2 in the atmosphere is necessary to ensure stable average temperatures across the globe. Ideally, carbon output and uptake would balance out, as it has for centuries. But since the industrial...