Ken Stewart, March 2012
Last April I demonstrated that changes in temperature precede changes in the concentration of atmospheric carbon dioxide.
Here I look at the increase in CO2 concentration more closely, and how it relates to atmospheric temperature and the Southern Oscillation Index (SOI).
There is no doubt that CO2 concentration has been rising, certainly since 1959, and that isotopic analysis shows this is largely due to fossil fuel burning.
But there’s more to the story.
This is a graph of CO2 concentration for the past 5 years, 2007-2011.
Some points to note:
The regular seasonal wave shows fluctuations.
There is a marked slowdown in February and March 2008 (following the temperature drop in the previous year), and another blip in March 2009 (resulting from the drop in energy consumption in late 2008.)
There is another slowdown in February, March, and April 2011.
The difference between consecutive peaks, and between troughs, varies each year.
These inter-annual differences interest me.
Here is a graph of the inter-annual monthly differences- the difference between the same months in consecutive years, e.g. January 2010 and January 2011.
2010 was a very good year for CO2 increase.
Note the huge slump in the rate of increase in April 2008, and the even bigger and longer slump around April 2011. In fact, April 2011 had the lowest inter-annual difference since July 2000.
The recent State of the Climate report claims that “Global CO2 concentrations in the atmosphere increased from 2009 to 2011 at 2 ppm per year” which is correct- the concentration in December of each year has risen by 2ppm. This was entirely due to 2010 however- by December 2011 the annual mean rise in concentration was down to 1.8ppm. 2011 was a below average year for CO2 increase. The BOM and CSIRO failed to mention this, I notice!
By comparison, here’s the same inter-annual rate of change for 1997 to 2001:
There’s no comparison, is there?
Here’s a graph (2007- 2011 again) showing the relationship between rate of change of temperature and rate of change of CO2. The temperature change has been doubled, and brought up to the same scale as CO2 change (2 is average).
Notice once again that rapid temperature change precedes CO2 change by a couple of months. However, other factors may be involved. Notice mid-2009.
Let’s zoom out and look at the 25 years from 1987 to 2011- actually, these plots show data up to February 2012.
I have marked in the eruption of Pinatubo, and the El Nino event of 1997-1998. CO2 change can still be seen lagging temperature change.
Now compare temperature change with SOI change. Note that SOI values are inverted.
Note: temperature change clearly lags SOI change by many months.
It has long been known that there is a link between ENSO events and CO2 concentration. So can we see a relationship between inter-annual change in SOI and CO2?
There is at least 10 months lag between SOI and CO2 change.
Now, smoothing with 12 month means:
Applying 10 months lag to the SOI and 4 months lag to temperature:
A pretty good match. El Ninos cause rapid CO2 increase. La Ninas and volcanoes are associated with slower CO2 increase.
Removing UAH shows the closer relationship between SOI and CO2. Here the 12 month mean of SOI change has been advanced 10 months.
Notice that in strong ENSO events the inter-annual change in CO2 can vary by more than 2 ppm per year.
The 12 month mean of raw SOI (scaled: /20, +2) shows El Ninos occurring nearly a year before CO2 increase; La Ninas have a weaker match.
Here are graphs of SOI vs CO2 since 1959: There are gaps in the CO2 mean because of missing months of data, after which 12 month means cannot be calculated.
Notice the same pattern: CO2 change lags SOI change by nearly a year.
Notice the very close match.
We can conclude that:
- CO2 concentration is increasing, and the rate of increase has doubled from 1 to 2 ppm per year in the past 50 years
- There is seasonal fluctuation in concentration
- CO2 concentration responds not only to temperature change but also to changes in the La Nina- El Nino cycle, nearly a year later.
The ENSO cycles strongly influence changes in CO2 concentration- not enough to overwhelm it, but enough to double or halve the rate of increase. Much more study is needed.