Yes, the atmospheric CO2 fraction has risen at a dangerously fast rate in the past 160 years, reaching levels not seen in millions of years

Once upon a time in a galaxy not very far away there was some scientific research that found the global carbon sinks (oceans, soils, vegetation) were not saturating — assuming, of course, that its general methodology and simplifying assumptions were in fact correct.

The research, by Wolfgang Knorr, had a title that tried to do too much in too few words: “Is the airborne fraction of anthropogenic CO2 emissions increasing?” And so when the American Geophysical Union published this interesting-if-true study, it issued a press release with the catastrophically wrong headline, “No rise of atmospheric carbon dioxide fraction in past 160 years.”

As an aside, Joseph Pulitzer’s “standing order to his staff” of reporters was: ACCURACY. TERSENESS. ACCURACY. For science reporting, you probably need to drop “terseness.” My motto is “better a long headline, than a wrong headline” — especially since a large fraction of people never go much beyond the headline, even more especially in the internet age, where the headline can truly take on a life of its own.

Now it’s kind of scary this particular headline got through whatever editors AGU uses, since it is directly at odds with what is arguably the single most famous chart of observational data in the entire climate arena, the Keeling Curve of Atmospheric concentrations of carbon dioxide (CO2):

In fact, not only has the atmospheric CO2 fraction (i.e. concentration) risen sharply in recent decades, it has risen at a rate that is unprecedented in the past million years (see “Humans boosting CO2 14,000 times faster than nature, overwhelming slow negative feedbacks”). As the author of 2008 study on this subject noted, “the average change in the amount of atmospheric carbon dioxide over the last 600,000 years has been just 22 parts per million by volume.” Humans have run up CO2 levels 100 ppm over the last two centuries! The author added, “”Right now we have put the system entirely out of equilibrium.


And that makes this a truly scary fable (see Science: CO2 levels haven’t been this high for 15 million years, when it was 5° to 10°F warmer and seas were 75 to 120 feet higher “” “We have shown that this dramatic rise in sea level is associated with an increase in CO2 levels of about 100 ppm.”).

Back to our story. The bad headline was then picked up by Science Daily, as is their wont:

[They later quietly fixed it, after being beaten up by the likes of Micheal Tobis and RealClimate — but how about printing some sort of apology/explanation?]

The anti-science gang leaped all over themselves to turn this story into a real fairy tale — without the benefit of actually having read and/or understood this study and/or, apparently, even the press release. Ken Ward Jr. of the WV Charleston Gazette did a great debunking of one such piece of muddled nonsense by the Charleston Daily Mail’s Don Surber, who declared on his blog that he had discovered “The Final Nail in the Global Warming Coffin,” ending “You can fool all of the people some of the time “” and some of the time is all Al Gore needed to make a pile of money.”

You can in fact fool some of the people all of the time, as the professional deniers prove every day. Ward then notes that in an editorial published yesterday, the Daily Mail summarized Knorr’s study this way:

Then there is the contention by Wolfgang Knorr of the Department of Earth Sciences at the University of Bristol in England that carbon dioxide levels in the atmosphere are about where they were 160 years ago.

Seriously. And they still haven’t retracted this egregious blunder.

For the spin by a true extremist, see “Climate Change Fanatics Shocked as New Scientific Paper Reveals Zero Atmospheric Carbon Increase.”


Knorr’s study is, of course, only about whether the fraction of human-emitted CO2 that stays in the atmosphere — the “airborne fraction — changes over time. He finds that it hasn’t. His work is at odds with work by Le Qu©r© and more than two dozen colleagues as part of the Global Carbon Project. For an open-access paper led by the GCP, see Canadell et al., “Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks.”


The GCP seem to me to be doing a much more impressive and thorough job of looking at all the data and analyzing it. Here’s what they find:

Between 1959 and 2008, 43% of each year’s CO2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO2 by the carbon sinks in response to climate change and variability. Changes in the CO2 sinks are highly uncertain, but they could have a significant influence on future atmospheric CO2 levels. It is therefore crucial to reduce the uncertainties.

Skeptical Science has an excellent analysis of the issue and these papers, “Is the airborne fraction of anthropogenic CO2 emissions increasing?” I must confess, though, that headline remains too opaque for the general reader. I’d prefer something simpler and clearer, like “Are the carbon sinks saturating or not.” SS notes that if the answer is no, it’s not really the “bombshell” WattsUpWithThat claims it is:

The 2007 IPCC verdict on the airborne fraction was “There is yet no statistically significant trend in the CO2 growth rate since 1958 …. This ‘airborne fraction’ has shown little variation over this period.” (IPCC AR4) I’m not sure the move from “not much happening” “to “still not much happening” warrants the label “bombshell”.

It is a tricky calculation with large uncertainties, especially the farther you go back in time, since we have less accurate measurements in key areas:

The airborne fraction is calculated from the rate of human CO2 emissions and changes in atmospheric CO2 concentration. The global increase in atmospheric CO2 has been directly measured since 1959 and can be calculated from ice cores for earlier periods. Primarily, CO2 emissions come from fossil fuel combustion with a lesser contribution from land use changes. Fossil fuel combustion is calculated from international energy statistics. CO2 emissions from land-use changes are more difficult to estimate and come with greater uncertainty. Land use emissions are estimated using deforestation and other land-use data, fire observations from space and carbon cycle modeling.

The emissions from land-use change (LUC) are especially tough because there are so many hard-to-measure factors, include CO2 uptake and loss from the soils. As the GCP explains:

Emissions from LUC are the second-largest anthropogenic source of CO2. Deforestation, logging and intensive cultivation of cropland soils emit CO2. These emissions are partly compensated by CO2 uptake from the regrowth of secondary vegetation and the rebuilding of soil carbon pools following afforestation, abandonment of agriculture (including the fallow phase of shifting cultivation), fire exclusion and the shift to agricultural practices that conserve soil carbon. Unlike fossil fuel emissions, which reflect instantaneous economic activity, LUC emissions are due to both current deforestation and the carry-over effects of CO2 losses from areas deforested in previous years.

Knorr makes a few simplifying assumptions about LUC which may or may not be correct, including this remarkable statement:

Another finding is that reducing the land use emissions by a scalar causes total emissions to be more consistent with a model of a constant airborne fraction… The analysis also shows that recent trends after 2000 can be explained by re-scaling land use emissions within their uncertainty ranges.

I’d welcome a comment from an expert on this tricky arena of modeling net CO2 emissions from LUC, but it certainly looks like Knorr has to change his scale factor over the past decade to get a consistent answer. That does not, of course, mean he’s wrong, but again GCP and Le Qu©r© et al. seem to me to be doing a much more comprehensive job of trying to model this.

SS notes:

There are several differences in methodology between Knorr 2009 and Le Quere 2009. Knorr’s result does not include the filtering for ENSO and volcanic activity employed by Le Qu©r©. However, when Knorr does include this filtering in his analysis, he finds a trend of 1.2 ± 0.9% per decade. This is smaller than Le Quere’s result but is statistically significant.

Knorr also finds the 150 year trend while Le Qu©r© looks at the last 50 years. This may be significant. If the airborne fraction is increasing, it is possibly a recent phenomenon due to natural carbon sinks losing their absorption ability after becoming saturated. Several studies have found recent drops in the uptake of CO2 by oceans (Le Quere 2007, Schuster 2007, Park 2008). However, with such a noisy signal, this is one question that will require more data before being more fully resolved.

If we’re seeing the saturation of the ocean carbon sink, it looks to be a relatively recent phenomena. After 10 years and more than 90,000 ship-based measurements of CO2 absorption in the North Atlantic, University of East Anglia researchers reached this stunning conclusion in 2007:

CO2 uptake halved between the mid-90s and 2000 to 2005.

In general, it would be awesome news if the sinks weren’t saturating. Many major climate models predict that they will — and, even worse, that some sinks will become major sources — leading to various positive or amplifying feedbacks:

Needless to say, this would complicate efforts to stabilize atmospheric concentrations of CO2 at levels needed to preserve a livable climate and makes action now all the more urgent.


The moral of our fable is write better headlines and read the whole damn press release and paper before writing about it. And since this is a fable for our times, what better way to end than with a talking bunny, Dr. Rabett, providing a version for children of all ages on Tobis’s “Only In It For The Gold”:

There is a very simple way to put it:We know the amount of CO2 emitted by us per year (pretty well) Call it X.We know the amount of this CO2 that stays in the atmosphere (the rest goes into the oceans and the biological bits of the land). That is, for reasonable purposes X/2 or 50%.That means that 50% of the CO2 that we emitted each year remains in the atmosphere.The question is whether the fraction is changing. Maybe only 48% is absorbed and 52% remains in the atmosphere. Knorr says the fraction is not changing. Canadell says the fraction remaining in the atmosphere is increasing. Canadell is really serious trouble. Knorr is only serious trouble.