The Carbon Cycle – Nature or Nurture?
By Ed Caryl
We know, from ice measurements, measurements at Mauna Loa, Hawaii, Barrow Alaska, and the South Pole, that atmospheric carbon dioxide has been increasing in our atmosphere since the beginning of the industrial age. We also know that temperatures have been increasing in that same time interval, as the earth warms up from the “Little Ice Age.” The proponents of the theory that man’s production of CO2 has resulted in this temperature increase, use that idea to predict future temperature increases based on our continuing to use fossil fuels and continuing to force an increase in atmospheric CO2. But, is the increase in CO2 due to man; or is the increase in CO2 natural, due to rising temperatures caused by natural means?
The natural CO2 flux to and from oceans and land plants amounts to approximately 210 gigatons of carbon annually. Man currently causes about 8 gigatons of carbon to be injected into the atmosphere, about 4% of the natural annual flux. There are estimates that about half of man’s emissions are taken up by nature. But is that true? Are there variations in the natural flux? Could those explain the CO2 increase?
Figure 1: From NOAA and the IPCC, here.
In June, 2011, Dr. Murry Salby gave a presentation at a IUGG meeting in Melbourne, Australia. This presentation was mentioned later on Judith Curry’s blog, and some others. DirkH brought this presentation to my attention recently in comments on NTZ, and I tracked down the YouTube version. In that presentation, Dr. Salby plotted the changes in CO2 and changes in global temperature and soil moisture. The soil moisture data is behind a paywall, but the monthly global temperature and sea surface temperature sets are easily and freely available from WoodForTrees. The annual carbon fossil carbon release figures are also available, covering nearly the same period as the Mauna Loa CO2 numbers.
The differential changes in CO2 are calculated on a two-year centered average of the monthly figures, then taking the monthly differential on that average. This gives a somewhat smoothed number, removing the annual cycles, yet preserving the timing.
Figure 2: Monthly change in CO2 at three measuring stations.
Figure 3: Magnified view of Figure 2.
Figure 3 is a magnified view of Figure 2, the interval from 1990 to 2000, showing the effect of the Mt. Pinatubo eruption in June 1992 and the El Niños of 1995 and 1998. The sharp cooling from the volcanic eruption appears before June 1992 because of the centered averaging to remove the noise and the annual variation.
Changes in CO2 seem muted at the South Pole, and the Barrow station is noisy as well as having a somewhat short record. Effects at the equator appear delayed at the stations closer to the poles. For those reasons, we will use the Mauna Loa record. It seems evident from Figures 2 and 3 that temperature influences CO2. But is it the global land and ocean temperature, or just the sea-surface temperature that is most important? Figure 4 is a plot of global surface temperature and monthly CO2 change:
Figure 4: Global surface temperature and monthly CO2 change.
The plots in Figure 4 look very similar; the question is how similar?
Here is the scatter diagram:
Figure 5: Scatter diagram of the data in Figure 4. Note the R2 value is 0.47636.
Here is the same comparison using sea surface temperature (HADSST2).
Figure 6: Plot of the monthly sea surface anomaly and monthly CO2 change.
Figure 7: Corresponding scatter plot showing an R2 value of 0.5528.
Sea surface temperature seems to be driving atmospheric CO2 changes. This makes sense because CO2 solubility in seawater is temperature dependent.
But what of man’s CO2 additions to the atmosphere? The data for carbon release is annual data, so the graphs are much coarser in appearance, and the change in CO2 must be annualized.
Figure 8: Annual change in fossil carbon use and the annual change in CO2.
Figure 9: Scatter diagram of carbon emissions change vs atmospheric CO2 change. Note that the R2 value is 0.05386, less than a tenth of the value of SST vs CO2.
It is ten times as likely that atmospheric CO2 is coming from natural sources, namely the warming ocean surface, as it is likely that it is coming from anthropogenic sources. The changes in CO2 track ocean surface temperature, not global carbon emissions. Burning fossil fuels is not increasing atmospheric CO2. Recovery from the Little Ice Age, driven by the sun, is causing the oceans to release CO2. It is temperature driving CO2 release, not the other way around. Just as it has always been.
As the sun gets quiet in the next few years, sea surface temperature will begin to fall, and the rise in CO2 will cease. If the sun stays quiet for 30 or 40 years, ocean surface temperatures will fall far enough to reverse the CO2 rise, the globe will enter a new little ice age, and things will get really interesting.