Carbon dioxide can be
both a cause of increasing temperature and an effect of increasing temperature.
The temperature over the last century has been increasing
due to an increase in CO2 mainly from the consumption of fossil fuels. We can
also see from paleo climate records that increasing temperatures can lead to
carbon dioxide being released from the oceans and acting as a feedback. If the
oceans warm then CO2 is released and this CO2 causes further warming.
Climate contrarians would like to suggest that the CO2 in
our atmosphere has built up from the oceans warming and equally has no effect
on warming. If true this would beg the following questions:- Where has the
carbon dioxide from fossil fuel burning gone and what has caused the warming? The contrarians don’t have coherent arguments for these questions though and instead
try to find evidence to spread doubt on global warming being caused by
increasing greenhouse gases.
Here I will describe some mathematical techniques that
involve playing with data to try to convince you that CO2 lags temperature even
in today’s changing atmosphere and temperatures due to the burning of fossil
fuels. This in the hope that: - readers will falsely infer that CO2 in our
atmosphere has built up from the oceans warming and equally has no effect on
warming.
First here are graphs showing changes in temperature and CO2:-
Figure 1 changes in CO2 over last 50 years.
Figure 2. Changes in temperature over the last 160 years
In figure 1 the trend in increasing CO2 can be readily seen
and also the seasonal variation that affects the CO2 in our atmosphere. This is
numerically consistent with the amount of CO2 emitted from humans with about
half being taken up by the biosphere and the oceans due to the increased partial
pressure of CO2. This is in spite of
oceans temperatures rising that would diminish this uptake. Interestingly the trend seems to have small random
variations due to natural variations of a secondary nature.
In figure 2 the trend in increasing temperature is also clearly
seen along with variations due to natural variations. These natural variations
include small changes in solar radiation, changes in ocean circulation such as
the El Nino S.O. , and changes in aerosols from volcanic eruptions blocking
sunlight. (There is also a period after 1940 of cooling. This coincides with the anthropogenic release
of aerosols, due to the increase of burning “dirty” coal.)
The CO2 trend is the main cause of the trend in the
temperature, and the seasonal changes in plant growth in the Northern
hemisphere is the cause the yearly cyclic variation seen in figure 1.
The cyclic 11 year cycle of solar activity with a slight decreasing
trend cannot account for the warming trend being of the wrong magnitude and
lately of the wrong sign but it CAN account for some of these variations.
If mathematically the trend is removed and the seasonal
cycle is removed then the variations can be seen clearer. However if this is
done we obscure any connections about the trend in CO2 and trend in temperature. There
are good mathematical ways of removing the trend and the seasonal cycles but Ole
Humlum crudely achieves this by “showing monthly values (in the graphs) of
DIFF12. This is the difference between the average of the last 12 month and the average
for the previous 12 months for each data series. This is shown here in figure 3
Ole
Humlum produced this graph to falsely conclude that CO2 lags temperature in today’s
atmosphere and Anthony Watts at WUWT falsely conclude that this is
evidence that suggests that man made CO2 is not the driver ofglobal warming.
What does a “Diff12”
do to data?
In short it smoothes
out variation to some extent and then differentiates as in normal calculus.
1. As in normal calculus differentiation this will turn a
linear trend to a horizontal line offset from the origin.
2. A sinusoidal cycle over twelve months will disappear.
3. Other variations will be differentiated as in normal
calculus.
What can we observe
from these graphs?
1. The blue graph will have the seasonal cycles removed and
the average value which is just slightly positive will be the trend of the
rising temperature over this time period expressed in degrees C per year. (This is the trend that is
caused by the trend in CO2).
2. The blue graph also has variations (other than the
seasonal cycle) which represent natural variation changes per year. (This is
likely the rate of change of variations due to mainly to the ENSO cycles).
3. The green graph shows the rate of change of CO2 again
with seasonal cycles removed. It shows if the last 12 month period had more or
less CO2 than the previous 12 months.
4. The green graph shows (assuming no errors in data
handling by Humlum) that these variations in CO2 lag the variations in the temperature.
(We can further see more clearly:- that the rate of CO2
build up is increasing slightly and the
rate of temperature build up has been roughly constant. The rate that
temperature is increasing is fairly constant is clearly seen here because any
peaks in temperature that are above the trend line in figure 1 are less likely
to be deceptively used as a starting point.)
Speculation:-
There is absolutely nothing wrong with adjusting the data in
this way as long as conclusions do not ignore the alterations that have been
done but rather take into account what has been done. If this has been done
accurately, one may speculate for example that some natural variation (ENSO)is
causing the sea to warm at a different rate and the ENSO is also affecting the short term variations of CO2.
(One may also speculate that the natural variation is
causing the sea to warm at a different rate and this change in warming then
affects the rate at which CO2 is absorbed into the oceans. This would imply
some direct evidence of a positive CO2 feedback.... I think a speculation that
Humlum or WUWT would resist).
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However this later speculation is unlikely to be the case.
a). TheCarbon Cycle Response to ENSO has been discussed by Jones et al 2001 and this supports the former speculation.
a). TheCarbon Cycle Response to ENSO has been discussed by Jones et al 2001 and this supports the former speculation.
“"Climatic changes over land during El Nino events lead to
decreased gross primary productivity and increased plant and soil respiration,
and hence the terrestrial biosphere becomes a source of CO2 to
the atmosphere. Conversely, during El Nino events, the ocean becomes a sink of CO2 because
of reduction of equatorial Paciļ¬c outgassing as a result of decreased upwelling
of carbon-rich deep water. During La Nina events the opposite occurs; the land
becomes a sink and the ocean a source of CO2."
b). In addition
to the land becoming a carbon sink during La Nina as described by Jones, Behrenfield et al suggest that oceanic phytoplankton would increase during La
Nina also, due to the upwelling off nutrients. This would work in the same
direction as suggested by Jones i.e. CO2 decreasing during La Nina years.
What can we conclude
from Humlum's graph?
We can conclude
the CO2 variations are not directly the driver of the natural variability in sea temperature changes. (If you want to see
clearly the correlation between CO2 and the rise in temperature you must
replace the trend that has been obscured.)
We cannot conclude
however that the trend in CO2 is caused by the temperature as implied by
Humlum.
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The short term variations in SST are not the cause of
the short term variations in CO2 but rather both of these variations have some
other common causes including ENSO. Further these correlations can be explained
and of course having nothing to do with the correlation in the trends.
