The Brighter Planet Blog

Our science team is ready and willing to take on your climate and energy questions! Just email us at scienceguys@brighterplanet.com.

Q: “How long does CO₂ stay in the atmosphere?”

A: That’s a great question, because the answer has a twist. The average molecule of CO₂ spends about four years in the atmosphere before it gets sucked up by a plant or dissolves into the surface layer of the ocean. But the carbon from the CO₂ doesn’t stay there — it cycles between plants, animals, soils, the ocean, and the atmosphere in what’s known as the ‘fast’ carbon cycle. As long as carbon is in the fast cycle, it’s contributing to global warming.

While some carbon leaves the fast cycle quickly, a significant portion stays there for hundreds or thousands of years. The main way that carbon leaves this cycle is when organic matter sinks to the ocean floor and becomes buried in sediment. Eventually it’s transformed into a fossil fuel or limestone (fossil fuels are so-named because they’re made of, well, fossils). Carbon in this ‘slow’ cycle is locked away for millions of years and does not contribute to global warming.

Burning fossil fuels causes global warming because it moves carbon from the slow cycle to the fast cycle at an unnatural rate—faster than it can be removed. Even if we stopped burning fossil fuels today, a thousand years from now there would still be lots of carbon causing warming while waiting in line to re-enter the slow cycle.

Even worse, we’re reaching the point where emitting more carbon actually shrinks the doorway into the slow cycle. As the oceans become saturated with CO₂, they absorb it at a slower rate. This creates a bottleneck for carbon entering the slow cycle where it no longer heats our atmosphere.

So, the dynamics of the carbon cycle dictate that when we release more CO₂ today, we’re ‘locked in’ to more warming in the future. What does this mean for us humans? We need to cut carbon emissions now to minimize the warming that’s coming down the line. The good news is that there are lots of ways we can all reduce our emissions today.

-the Science Guys @ Brighter Planet

For more information on how long CO₂ and other greenhouse gases affect our climate, check out FAQ question 10.3 from the IPCC Working Group I 4th Assessment Report.