"Has atmospheric CO2 decreased? A different way to look at CO2 changes"

[Deja Q]

http://wmbriggs.com/blog/2008/02/06/has-atmospheric-co2-decreased-a-different-way-to-look-at-co2-changes/


The black line is the actual CO2 data, the two background colors representing, before 1958, estimates of CO2 based on ice cores, and after that on measurements from Mauna Loa. The green line is a suitably normalized estimate of the human population. Both increase at what looks like roughly the same rate. Right?




This graph is complicated, so let’s take our time to understand it. The horizontal, or bottom, axis is still time. But now the black line is the yearly change in CO2. For example, in 2007 the CO2 was measured to be 383.32 parts per million (ppm) and for 2006 it was 381.83 ppm. The change, which was an increase, was 1.49 ppm. We measure this change for each year and keep the results, so that we can see the rate of increase (or possible decrease or no change) for each year. We could plot this raw change through time, but a lot of detail is hidden because the increase is exponential (the same shape as the cartoon plot above).

Instead of a raw plot, we take the log of all values so that detail can emerge. This should not change conclusions based on the data in any way, and it does allow us to see it better (technical note: the value of 1.2 was added to all values because some changes were negative and, without using complex numbers, we cannot take logarithms of negative numbers).

The detail pops now, doesn’t it? The first thing to notice is the marked qualitative and quantitative differences in the Mauna Loa and Ice Core estimates. The two methods are obviously not directly compatible, a fact which was hidden in the raw (non-differenced) plots. This makes decisions about the rate of increase of CO2 across the two regimes trickier than is commonly thought.

There are even times when CO2 has decreased, i.e. removed from the atmosphere, from year to year (according to the measurements used): these are the points below the dotted-dashed line at 0. These times were roughly 1820, 1831-1838, times before wide-scale industrialization, and 1942-1944. 1942 to 1944? This was certainly a time in which the entire world, if you recall, was intent on adding as much of everything to the atmosphere that it possibly could. So this result is strange. One possibility is measurement error: something might have gone wrong in the way the ice cores were processed.




Article has more.

[Buzz Clik]

1. I wish he would have included the log change plot.

oh, well.

[jimlup]

2. I don't follow your discussion...

You say the curve "pops out" but I don't know which curve you are referring to. I assume you mean the green curve.

It isn't surprising to me that the values are sometimes negative since we know that lots of CO2 is absorbed by the yearly breathing process. While human's were dumping as much CO2 as they possibly could during these periods it was still probably in close equilibrium with the absorption rate thus making negative values possible even if the long term trend is up wards.

Further, you are setting yourself up for poor statistics and a graph that is very sensitive to small uncertainties since you are taking the difference of large values then adding an offset to it and finally taking the logarithm of that value!? Very weird, especially adding an offset before taking the logarithm ... I'd need to think very carefully before I started trying to draw any significant conclusions for that graph.

[Dead_Parrot]

3. I don't quite get what he's asking

If he means, "has atmospheric CO₂ ever decreased", then yes: It was around 7,000 ppm in the Cambrian, and you don't need a degree in advanced statistical wrangling to work out it's spend more time going down than up in the intervening years.



On the other hand, if he's asking "has atmospheric CO₂ recently decreased", then no: You can fuck around with logs, differences and offsets 'til your eyes bleed, but there's not really that much wriggle-room in the raw data.



That, if you squint hard enough, you can maybe see ten years in the last 2 centuries where things have actually been normal - decreasing CO₂ - is really nothing to get wildly excited about.

The other 190 years are still fuck-ups.

Last year, btw, CO₂ increased by 2.28ppm. Makes you proud to be human, doesn't it? :(

[losthills]

4. A graph is an illustrated opinion.

Nothing more.

[Viking12]

5. Actually, its complete bullshit

Nothing more

http://www.realclimate.org/index.php/archives/2007/05/beck-to-the-future/