The Blackboard:

Anthony Watts recently posted an interesting observation: The seasonally adjusted CO2 concentration measured at Manau Loa dropped two months in a row. He illustrated this with a graphic available at NOAA which shows a two month drop in the seasonally adjusted values of CO2. Needless to say, “some”, have jumped all over this complaining that:

Yet some are making a big deal out of a single month’s drop in seasonally adjusted CO2 concentration, one which turns out not to be at all unusual. Some have made a big deal of the fact that CO2 concentration is rising linearly while emissions are increasing — when in fact the rise is most certainly not linear.

“Some” have suggested this? Who? I may need a category for post starting with “Erhmm…”.

I previously noted that a blogger who has taken on the form of a Bulldog “rebutted” my falsification of the IPCC AR4 prediction of 2 C/century warming for the early decades of 2000. How? by performing a entirely irrelevant data comparison between IPCC TAR predictions of lesser warming during the decades beginning in 1990 (a different time frame). Needless to say, I couldn’t fail to notice that this blogger’s most recent “rebuttal” post rebuts something no-one appears to have suggested.

Yes, today, on April 8th, figures, curvefits, fancy filters show that the one month drop in CO2, while fairly large, is not sufficiently large to be “remarkable”.

Why would anyone rebut the non-existent claim about the one month drop, without citing anyone who has suggested any such thing? Well, not citing or linking is a good way to prevent readers from discovering there is no such claim. It is rather well known that rebutting the unmade claim that is vaguely similar to something made by a widely read blogger is generally easier than addressing arguments anyone actually made. In this case, the “one month” claim might seem vaguely related to the contents of an article Anthony Watts actually posted, which simply shows some data which happens to include a two month drop in the detrended (i.e. seasonally adjusted) values.

It turns out the two month drop in the detrended values represents a record drop. See the circled points in the figure below?

So, I bet you are wondering how I know Anthony, posted only because the two month drop struck him? Well, because responding in comments on April 4th — well before the “rebuttal” appeared, Anthony said:

I looked at 2004 also, but this seems a little bit different. 2004 has one month of drop, this has two, with a larger effect on the running mean. Though, part of that could be an endpoint effect of the data.

I don’t know what other people think, but I consider something that happens onces ever 150 times is fairly remarkable– that is, worthy of making a remark as Anthony did.

Does a two month drop this large mean the relentless climb in CO₂ has leveled off? Does it mean much about climate change? Who knows? I think most would suggest it’s premature to declare the rate of rise ended. As Anthony Watts observed:

It will be interesting to see in the coming months what happens globally,. . .

Yes. It will be interesting.

Records do get broken, and unusual, even remarkable things happen. This ties for the record drop set back in the 60’s. The current drop may be due to the cool seas associated with La Nina, in which case, CO₂ will rise when the next El Nino occurs. Or, the current drop may be instrument error; NOAA’s web page tells us that we should wait for post-calibration before taking recent data as gospel.

In any case, we are still emitting carbon at a significant clip; so the CO₂ will likely resume rising as it has in the past. If so, this will simply be a blip.

The event is nevertheless worthy of remarking. I’m sure we’ll all be watching for next month’s data and also checking the data after NOAA runs its normal post-calibrations..

References

1. Data from NOAA. My chart is created by subtracting two month lagged values of CO2 in the “detrended” column, which represents seasonally adjusted values.

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