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Climate Change and CO2 400 ppm

If you follow the climate news to even a moderately obsessive degree, then you’re aware that we’ve been creeping up on 400ppm, which is to say, an amount of CO2 in the atmosphere that’s 400 parts per million, by volume.

As the above graphic and stories by BBC (Carbon dioxide passes symbolic mark) and AFP (Carbon dioxide in atmosphere hits historic high) and soon, no doubt, many others point out, we’re there.

So, what does it mean? At one, arguably superficial level, it means basically nothing. 400ppm is no more important than, say, 395ppm or 413ppm. In fact, “400″ is a nice, round number, which tends to give it undue significance in the human mind, purely by biological accident. If we had evolved with a different number of fingers and counted in, say, base 12, then the value we associate with 400 would would be 294, and the “nice, round number” of 300 (base 12) would be 432 in our base 10 system.[1]

That piece of rampant pedantry aside, 400ppm is of extreme interest for two reasons:

First, it’s too bloody high. One can argue endlessly about what the exact right figure is, given that such a determination involves perversely squishy yet undeniably important fields like politics and economics, but I’ve yet to hear anyone who wasn’t financially or ideologically compromised claim that the ideal level was near or above 400ppm. The famous calculation by Hansen that the right answer is 350 seems about right, which makes this and the following point quite frightening. And for those who might have forgotten it, the pre-industrial level was roughly 280ppm, which makes 400 a nice, round 50% increase.

Second, the CO2 level isn’t just rising, it’s doing so at a high rate. For more data than you can shake a dead computer mouse at, see the NOAA page, Trends in Carbon Dioxide. Note the scrollable list near the bottom of that page that lists the annual increases in CO2, the one that says we added a whopping 2.66ppm from 2011 to 2012. Over the last five years, our atmospheric handiwork averages a bit over 2.08ppm/year increase in CO2.

From a communications standpoint, this number will likely be utterly meaningless. Even if we get “lucky” and the mass media in the US recognizes that we passed this milestone and points out that it’s been millions of years since there was this much CO2 aloft, it will almost surely be nothing more than a 15-second, “ain’t that a hell of a thing” filler before we get back to the latest celebrity or political dust up that will be forgotten before the daily CO2 level reaches 400.5ppm. I want to be wrong about this, obviously. I would dearly love to see 400ppm be some sort of wake up call for the mass media, the thing that finally drills down through their layers of cognitive insulation and convinces them that climate change is, at a bare minimum, the story of the century.

[1] An old programmer friend of mine once observed that we got it wrong, and instead of base 10, we should be counting in base 8 because our thumbs are not digits but parity bits. I’ll let those of you who get that joke explain it to the 99% who don’t.

Lou Grinzo's picture

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I K's picture
I K on May 12, 2013

If you buy a soda and open the can, that fizz is because the dissolved carbon dioxide is leaving the liquid. This is due to partial pressure. The opposite also happens but you can’t heat or see it so clearly. If you took a can of perfect water and nothing else at all in it, the moment you open it carbon dioxide from the air would “fizz” into this can of perfect water

As noted before it is also the physical phenomenon which allows your pet fish to stay alive in its bowl. It draws the oxygen out of its water and expels carbon dioxide into its water. Partial pressure then ensures that the carbon dioxide “fizzes” out of the water and oxygen “fizzes” into the water.

This system is also true for the whole world. The amount of carbon dioxide moving into and out of the oceans from the air is dependant on the concentration of the carbon dioxide in both fluids. Right now it appears partial pressure is forcing the majority of the added CO2 to dissolve out of the air and into the oceans and soil.

So my question is, what exactly is the relationship of these concentrations and the relative forcing? If it is exponential (as would be expected) then as CO2 concentrations increase earth will CCS more and more of what we add until soon it CCS 100% of what we add.

Paul Ebert's picture
Paul Ebert on May 14, 2013

It is true that the ocean is absorbing quite a bit of the CO2 we are adding, but this is not a good thing as best as I have found in the research.  It is causing acidification which is killing phytoplankton and other lifeforms that utilize carbonate (corals and anything with shells).  This is bad for two reasons.  First, phytoplankton is the bottom of much of the oceanic food chain, so phytoplankton loss endangers the entire food chain.  Second, phytoplankton is a key converter of CO2 into O2, so its loss becomes yet another forcing towards greater CO2 concentrations.

If you can point me to research that indicates that the oceans or soil can beneficially sequester CO2, I’d be very interested.

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