CO2 and Temperature

Ken Stewart, April 2011

Surely this has been shown before.  If not, it should have been.  If it has, it bears repeating.

As we all know,  an increase in carbon dioxide concentration leads to an   increase in global temperatures.  Right?

Wrong.  Exactly the reverse.

Now don’t get me wrong. There is a greenhouse effect, whereby greenhouse gases have made the earth’s temperature more than it would be without them.  We are pumping extra carbon dioxide into the atmosphere, so that CO2 levels are steadily increasing.  And temperatures appear to have been rising- certainly atmospheric temperatures have risen since 1979.

However, since carbon dioxide concentration measurements began at Mauna Loa in 1958, temperature has changed before carbon dioxide has.  That’s right, a change in temperature leads to a change in carbon dioxide concentration.

Here’s a graph showing CO2 concentration (reduced to compare with the temperatures) and global mean temperature recorded by UAH.  Red is for temperature, and CO2 concentration is “suitably” black.

Figure 1.

It is plainly obvious that CO2 levels are rising, and temperatures have been rising.  Temperatures fluctuate up an down quite a bit, and there is a regular annual wave in CO2 concentration believed to result from seasonal Northern Hemisphere  biomass growth and dieback.  It seems intuitive that with seasonal temperature rise, trees and grasses grow rapidly, absorbing CO2, and this causes CO2 concentration to fall.  In autumn and winter, as temperatures fall, the rotting biomass releases CO2.

Yet it’s not so simple.  I’ve included a 12 month running mean.  The small reduction in the rise of CO2 can be seen in the early 1990s, and a small lift about 1999-2000.  What could explain these variations?  Variations in energy consumption?

Nope- Mt Pinatubo and the 1998 El Nino.

Here’s a graph of changes in temperature and changes in CO2 concentration.

Figure 2

I calculated the difference in temperature and CO2 between each month and the month preceding, and smoothed the results with 12 month running means, which therefore overlap all seasons.  Remember this represents change in temperature and CO2, not absolute values.  Remember also that this is worldwide, so is not limited to seasonal changes.  Notice that change in temperature occurs before a change in CO2.  There appears to be a lag of from 3 to 9 months, and possibly 12 months, especially marked when there is a rapid change in temperature, and not so rapid for smaller change.  Smaller, slower changes appear to be overshadowed by the large seasonal variation, depending on the timing.

I also compared CO2 with HadcruT temperature data from 1958, the start of the Mauna Loa record, although I am not fond of any surface record because of potential problems with surface station siting and adjustments.  Still, it is a temperature record, and I am not interested in absolute temperature but change.

Figure 3

Again note that after a 3 to 9 month lag behind temperature change, sometimes up to 12 months, CO2 concentration changes.

It has been suggested that the small dip visible in Figure 1, in 2008 (circled), is a response to reduced industrial output from the Global Financial Crisis.  Figure 2 and Figure 3 show that this was not the case, and that the drop in CO2 was a response to lower temperature.

Conclusion:

• Carbon dioxide concentration, while increasing year to year, responds to temperature change after a lag of some months- not the reverse.
• We can predict that the CO2 concentration over the 2011-2012 period will have a smaller increase than normal, following the dropping temperatures.
• Provided that global CO2 output continues at current rates, we should be able to project future CO2 concentration from current temperatures several months in advance, and indeed from trends in the Southern Oscillation Index.
• It should be possible to quantify the relationship between temperature change and CO2 change.

We live in interesting times!