There are good reasons to change the way data is presented, for example to highlight correlations or for improved presentation purposes. In the hands of the pseudo-scientist however there are numerous pitfalls performed either wittingly or unwittingly arriving at clearly false conclusions. This is particularly true with attempts to discredit climate science.
A coherent and consistent explanation is generally accepted
for the rise of CO2 since the start of the industrial revolution. This
explanation includes the causes for the trend in CO2 and different causes for
the variations in CO2. There is little doubt that the trend is caused by human
activity and in particular the burning of fossil fuels just by considering the
volumes involved. The trend appears to be approximately half the rate of
emissions. The variations in the concentrations of carbon dioxide are more
complex and interesting and can throw light on a number of different causes and
effects(1). There is the obvious seasonal cycle that is apparent in
the keeling curve. There are other short term variations that are concerned
with changes in atmospheric and oceanic circulation such as the ENSO cycle.
Focussing on the
Once the trend in the CO2 concentration rise is identified
(although caution is needed here) it can be subtracted from the data to reveal
more clearly the variations.
Seasonal cycles become apparent that are concerned with the
seasonal decay or growth of plants particularly in the northern hemisphere.
Identifying a consistent cycle or by using appropriate filters allows this to
be readily removed from the detrended data leading to variations that are
closely linked to the ENSO cycle(2).
During the El Nino years with increased sea surface
temperature, SST, there is increased CO2 and conversely during la Nina years
there is decreased CO2 levels. One may speculate that this increased CO2 associated
with the El Nino is a direct result of warming waters (net) absorbing less but
evidence suggests that this is not so and more to do with photosynthesis which will be discussed. Furthermore
these variations in CO2 lag(1,2,3) the variations in
SST by several months also to be discussed.
Plants preferably take up the lighter C12 isotope over C13
and hence the C13/C12 ratio will increase during seasonal plant growth or
decrease when plants decay or when plant derived fossil fuels are burned. When
we look at the trend in CO2 rising we see that the C13/C12 ratio falls as is
consistent with burning of fossil fuels.
(There are two other ways that the C13/C12 ratio could fall:-
1. The biosphere is decaying simultaneously as we emit fossil
fuels but this would require the oceans take up all or most of what we emit.
There is no evidence that the biosphere is decreasing and I don’t think anyone
would consider this as a plausible explanation. If this started to happen in the
future then it could indicate a disastrous situation involving a positive
feedback to our emissions.
2. Lighter Carbon from the mantle is being released in phase
with our emissions! Again not a realistic observation that also fails to
describe what is happening to our emissions.)
The seasonal cycles.
The variations in the
carbon isotope ratio follow the growth and decay of plants as expected. Keeling4.
In the northern hemisphere with more land mass and more plant growth in the summer
months CO2 levels drop due to the extra photosynthesis, and also the C13/C12
ratio increases due to the sinking of more lighter carbon.
The ENSO cycles.
During the La Nina the C13/C12 ratio increases (after factoring out the seasonal changes and changes due to the trend) and this is
not consistent with the explanation of SST directly affecting the solubility of
CO2 in sea water but more indicative of increased photosynthesis during plant
growth. Now we have an explanation of the detrended CO2 concentrations (with
seasonal variations removed) lagging the changes in SST. The SST is associated
with ENSO cycles. The La Nina component of this causes nutrient rich water to
upwell in the eastern pacific encouraging plant growth3 and the
Southern oscillation associated with this increases the net precipitation over
land globally, and encourages plant growth1,2 months later. A temporary decrease in the rate of sea level rise is consistent with this.
Sea surface temperatures have been rising in the tropical
Eastern Pacific through July and August 2015. The atmospheric and oceanic
circulations associated with this is of course the ENSO cycle. At the present
time we are experiencing the onset of what may likely be a large El Nino. This
will have an impact that will differ regionally and globally affecting plant
growth on land and in the oceans and have a resulting affect on the sourcing
and sinking of carbon dioxide. It is to be expected we will see less upwelling of
nutrient rich currents in the eastern ocean, less rain fall on land globally,
more drought globally (if not California) and more wild fires globally. All
these impacts will almost certainly result in an extra increase in CO2
concentrations, over what would otherwise be expected from our emissions, that
are likely to become apparent and that will lag the increase in SST observed in 2015.
1. Interannual extremes in the rate of rise of atmospheric
CO2 since 1980 Keeling et al