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CO2 levels highest in over three million years

Temperatures may keep rising for decades after this level is hopefully stabilized

Keeling curve graph showing rising CO2 levels.

Atmospheric CO2 (carbon dioxide) levels on top of Hawaii’s Mauna Loa hit a record high of 401 parts per million earlier this month, and as we are still a month or so away from peak CO2 levels, this record will likely be broken. Just what does this mean? Let’s start off be looking at the history behind our tracking of CO2 levels, and finish off by looking at what these high levels might mean.

Carbon dioxide and water vapour are considered to be two of the most important greenhouse gases. The Earth needs greenhouse gases; without them we would be a much colder place and life as we know it could not exist. On the other side of the coin, too much greenhouse gas and the Earth will grow warmer, possibly to the point that once again, life as we now know it could not exist. As our technology has increased over the last couple of hundred years, so has our ability to influence certain greenhouse gases through pollution. Tracking the levels of greenhouse gases gives us an idea of just how much we are changing or influencing their levels.

In 1958 Charles Keeling began to accurately measure carbon dioxide levels. He decided to take the measurements at the Mauna Loa Astronomical Observatory, located on top of an inactive volcano in Hawaii. He picked this site because it was far away from any major sources of carbon dioxide and should therefore provide a good value that will be representative of an average number for the Earth.

Graph showing CO2 levels as measured from ice core data.
CO2 levels from ice core data for the last 800,000 years. The end of the graph shows how rapidly CO2 levels are changing. photo: Scripps Institution of Oceanography

If you look at the two graphs included with this article, you will see that in the first graph, the values for CO2 follow a very rhythmical seasonal pattern, with levels topping out in early May and then bottoming out in November. This seasonal up-and-down pattern is the record of our planet breathing — or rather, the plants breathing. The majority of land and plants on our planet are in the Northern Hemisphere. During the summer months, plants are actively growing and taking in large quantities of CO2 and we see atmospheric CO2 levels drop. During the winter, plants no longer take in CO2 but bacteria and animals continue to produce CO2 and we see the values go back up. This graph has become known as the Keeling curve.

The other thing you probably noticed about these graphs is that the amount of CO2 in our atmosphere has been steadily increasing in recent times (since about the 1700s) and that the pace of this increase has become very rapid over the last 50 years. As noted above, CO2 levels have now gone above 401 ppm and will likely go higher over the next month or two. What is the significance of 400 or 401 ppm? Nothing really. While it is a record value, we are creating record values every year. It’s simply a symbolic number; we are now over 400 ppm and at the current pace will likely hit 450 ppm well before 2040.

From the Alberta Farmer Express website: Detailed look at the fifth IPCC report

So, when was the last time the planet has seen values this high? The records from Mauna Loa only go back 55 years, but we do have what is considered a fairly good record set going back 800,000 years. These records come from the Antarctic ice sheet and were obtained from samples of air trapped in bubbles within the ice sheet. Looking at these values (second graph) we can see that over the last 800,000 years values have fluctuated between 200 ppm during ice ages to around 300 ppm during the warmer periods. Using slightly less reliable geochemical methods we can extend the CO2 records back much further and we would have to go back about three million to five million years to see the levels we are now experiencing.

The big question out there is, just how high can this number get before we are really in trouble? No one is absolutely sure, but best estimates are around 430 ppm. So some of you are now probably thinking that we have a good 20 years to figure this all out and hopefully fix it, but that’s not really the case for a couple of reasons. The first one is that global temperature increases lag behind increases in CO2. This means that while the level of 430 ppm shouldn’t increase global temperatures beyond what we consider to be safe, temperatures will likely continue to increase for several decades after this value is hit and hopefully stabilized. The second reason we don’t really have 20 years to fix this issue is that CO2 levels are rising at about 55 per cent of what they should be based on our emissions. Therefore, to keep CO2 levels close to where they are now means we would have to cut CO2 emissions by around 55 per cent, which we know won’t and can’t happen without a major impact to the world’s economy. The 45 per cent of CO2 emissions that are not making it into the air are being stored in what are known as CO2 sinks, the largest of these being the world’s oceans. Eventually these sinks or storage areas will fill up and when they do, atmospheric CO2 levels will increase very rapidly. Some estimates place a final possible value at nearly 1,600 ppm by the time we use up all of our fossil fuels!

One final note on this topic. The measurement project that created the Keeling curve is in danger of being discontinued due to budget cuts. If you are interested in learning more and possibly helping out you can check out

About the author

Co-operator contributor

Daniel Bezte

Daniel Bezte is a teacher by profession with a BA (Hon.) in geography, specializing in climatology, from the U of W. He operates a computerized weather station near Birds Hill Park.

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