Back on April 6th of this year I made an observation about the trend in the CO2 data from the Mauna Loa Observatory dropping and possibly “leveling off”.

For that I was roundly criticized by those “in the know” and given the full Bulldog treatment.

Well, it’s happened again. With the release of the July data from Mauna Loa Observatory, a new twist has occurred; this time there’s been a first ever trend reversal of the monthly mean CO2 levels from January to July. Here is the familiar Mauna Loa graph:

Source data: http://www.esrl.noaa.gov/gmd/ccgg/trends/

In the NOAA graph above, note the drop in the first few months of 2008, and the slightly muted rebound afterwards. Clearly something changed and the uncharacteristic drop in CO2 levels has been recorded by the world’s premiere CO2 monitoring station.

By itself, that blip isn’t much news, as there have been similar blips in the past, such as in 2004. But where it really gets interesting and unique is when you compare the seasonal difference, between, January 2008 to July 2008 levels against the rest of the Mauna Loa CO2 going back to 1958.

First let’s look at this year and last year in a magnified portion of the Mauna Loa CO2 monthly mean data:

Source data via FTP: Mauna Loa CO2 monthly mean data

Note that the January 2007 to July 2007 Delta was a positive 1.41 PPM, but this year, the January 2008 to July 2008 Delta value was negative at -0.42.

Going back through the data to compare previous January to July values, it has become clear that this is a unique event in the history of the data set. A value lower in July than January has never happened before. Prior to 2008, there has always been a gain from January to July.  This is a 6 month “seasonal”period from January 30th to July 31st, when the end of month data is released.

Below is the data table with the January and July values highlighted for your inspection.

What this means I cannot say. It may be noise, it could be a fault in the data gathering or in the measurement instrumentation. It may be an effect of increased ocean CO2 solubility due to the global cold snap we’ve been having the past few months. Or it may be related to the biosphere respiration changing in some way we don’t know about.

This may signal a change,  or this one time event may in fact be that, one time. It may not happen again next year, we simply don’t know. But, it is unique and thought provoking.