Carbon emissions

CO2 emissions are not the same as CO2 ppm

by Elisabeth Robson, author and software developer

Nature Bats Last,

25 March, 2015

In March, 2015, the International Energy Agency (IEA), indicated that their data show that “global emissions of carbon dioxide from the energy sector stalled in 2014, marking the first time in 40 years in which there was a halt or reduction in emissions of [CO2] that was not tied to an economic downturn.”

Since that hit the press, I have seen numerous people confuse CO2 emissions with CO2 ppm in the atmosphere. These are two very different things.

CO2 emissions is a measurement of the billions of tons of CO2 we emit into the atmosphere, by year. It’s like if you put all the CO2 into big cups, the measurement of CO2 emissions is how many cups you’d fill with CO2.

A graph from the IEA shows the mostly steady increase in emissions through 2012:



In 2013 we emitted 32.3 billion tons of CO2, and in 2014 we emitted the same amount: 32.3 billion tons of CO2. It’s still a huge amount of CO2! Especially when you compare it to the amount we emitted not that long ago:


So it’s clear that even if our CO2 emissions did not increase in 2014 over the amount we emitted in 2013, we’re still emitting a heck of a lot of CO2.

CO2 ppm

Now let’s look at ppm or “parts per million”. CO2 ppm is a measurement of the number of molecules of CO2 in the atmosphere compared to other kinds of gases. So if you take one million molecules of air, and you sort them into different kinds of molecules, about 400 of those million are CO2 molecules (based on our current CO2 ppm levels of about 400). The rest is a mix of nitrogen, oxygen, and argon, plus a few others in very small amounts.  An increasing amount of methane is also present in our air these days, but that’s another story.

You can see the current measurements at the Mauna Loa observatory where the “official” CO2 ppm is measured (although CO2 ppm varies around the world), and you can see trends nicely laid out at the Scripps Keeling Curve web site. At the Scripps web site, if you mouse over “One Month”, you can see that we hit a new record of 403.8 on March 10, and if you look at the “Full Record” you can see the steady incline of CO2 in our atmosphere measured in parts per million. The six-month graph ending mid-March, 2015 is:


As you can see, CO2 levels measured by ppm in the atmosphere continue to rise overall, with variations on both a daily basis as well as over the course of a year based on winter and summer emissions of CO2 (mostly by plants).

So, it’s certainly true that as we emit more CO2, we find that the level of CO2 goes up—that is, the CO2 ppm level increases. But even if our CO2 emissions flat line, our CO2 ppm will continue to go up, because we’ll still be emitting CO2.  In fact, CO2 levels in our atmosphere, measured by parts per million, will continue to increase as long as we continue to pump unreasonable amounts of CO2 into our atmosphere. What’s reasonable? Well, at this point unfortunately, a reasonable number is actually a negative number. We not only have to stop emitting CO2, we have to start taking it out of the atmosphere so that the CO2 ppm will go down—preferably back down to 300 ppm or below. As long as we continue to emit any CO2 into the atmosphere from industrial civilization—in other words, above and beyond what would normally be emitted by life on the planet without industrial civilization—then we are emitting too much, because we have exceeded the planet’s ability to absorb that CO2 (say into the oceans or into new living plants).
 
Lots of people are applauding the fact that CO2 emissions in 2014 did not go up over 2013 levels. They say that means economic growth is “no longer tied to emissions,” which is, of course, ridiculous unless we could somehow magically replace all fossil fuels with alternatives overnight. But aside from that issue, even if CO2 emissions really have leveled off (I’ll believe that if/when I see multi-year data — one year does not a trend make!), they are still at levels that will cause CO2 ppm  to continue to climb, and they are still at levels that will cause catastrophic climate change

In short: CO2 emissions does not equal CO2 ppm!