The last thirty-one years climate from satellite measurements of temperature

Much has been said and written about the various trends in global temperature and their relationship to the ever increasing concentration of CO₂ in the atmosphere. There are some doubts about the terrestrial records of global temperature, but differences between them are not statistically significant. Since the continuous temperature record of the lower troposphere temperatures is available, it seems appropriate to consider its possible interpretation.

The lower troposphere satellite records from the University of Alabama at Huntsville are used entirely in this exercise and the total global temperature anomaly record, based on the mean of the temperature anomalies over the period from 1979-1997 is shown in Figure 1.

 

Figure 1 The record of monthly global anomalies over the 1979-2009 period

There is a positive trend and very few of the individual records fall outside the limits shown of ± one standard deviation. The positive trend is statistically highly significant.

A graph of the variations in annual global temperature anomaly and CO₂ concentration is shown in Figure 2. Annual values are used in this case because of the considerable seasonal variation in CO₂ concentration.

 

Figure 2 Plots of the annual mean values of global temperature anomalies and CO₂ concentrations measured at Mauna Loa

Although it is an approximation to draw straight lines on such graphs, other algebraic possibilities are no better and the two sets of data have a correlation coefficient of 0.64 indicating a possible causal relationship, the warming arising from the extra forcing of the greenhouse effect provided by the extra CO₂.

This is not the end of the story by any means and since latitudinal and land/ocean data are available these should be considered.

Figure 3 is a histogram showing the decadal temperature trends in various latitudinal areas of the globe.

 

Figure 3 Decadal temperature trends of latitudinal areas showing the differences between land and ocean in the various regions

It is very clear that virtually nothing is happening in the Southern Hemisphere and that all the action is in the north. The relatively small global trends cover up much larger ones that are occurring in the north. These are worth extra study.

Figure 4 shows a map of the globe with the variations of atmospheric concentration for July 2009.

 

Figure 4 The global distribution of CO₂ concentration, July 2009

The main generation of CO₂ is in the northern mid-latitudes and the blue areas indicate the 'sinks'; the oceanic areas where the gas is dissolving in the water. The map is consistent with the BP Statistics of fossil fuel consumption which shows that a remarkable 93% occurs in the northern hemisphere.

The data for the northern extra-tropics, between latitudes 20 N and 70 N show a small difference between the trends for the land and ocean and the overall data for that region may be dealt with without considering that difference.

Figure 5 shows the temperature record for the northern extra-tropics and includes the trend lines for the data and those representing ± one standard deviation.

 

 

Figure 5 Temperature data for the northern extra-tropics; 20 N - 70 N

As with the global data very few points fall outside of the ± one standard deviation limits and the trend is statistically extremely significant. The points on the graph beyond the spike of the 1998 El Niño event are of recent intense interest since they show no warming and parts of the global record have been used by some sceptics to claim that there is cooling.

Figure 6 shows the data from 1997 for the northern extra-tropics.

 

Figure 6 Temperature data for the northern extra-tropics from 1997

Figure 6 does indicate a very small cooling trend, rather than the positive trend that might be expected if the continued increases in atmospheric CO₂ concentration are producing their expected warming. This indicates that whatever that warming might be, it is being countered by an equal and opposite cooling trend over the selected period.

That the continual emissions of CO₂ into the atmosphere from land change and fossil fuel burning is causing the increase in CO₂ concentration is in very little doubt. Figure 7 shows the variations in anthropogenic emissions and the atmospheric CO₂ concentration over the 1979-2008 period.

 

Figure 7 Variations in anthropogenic emissions of carbon and the atmospheric CO₂ concentration

The data on which Figure 7 is based show remarkably similar, almost linear trends and statistically the correlation coefficient between the two sets of data is 0.97. This does not prove causality, but offers a very strong suggestion that the emissions of anthropogenic carbon are mainly responsible for the increases in CO₂ concentration. There is very compelling evidence for the linkage from the study of the distribution of carbon-12 and carbon-13 isotopes in the atmosphere and in the oceans. Fossil fuels are derived from rotting vegetation that is assisted by bacterial action as well as chemical decomposition. All chemical processes have rates that are dependent to some extent upon the masses of the reacting substances. Both carbon-12 and carbon-13 undergo identical chemical reactions, but the heavier isotope is discriminated against in the products of the reactions. So, in the formation of fossil fuels the carbon-13 isotope has a considerable and measurable lower representation than it does in the vast amount of carbon in the planet. When the fossil fuels are burned, the resulting extra carbon entering the atmosphere has the tell-tale signature of a diluted ¹³C/¹²C ratio. The atmospheric carbon is being progressively diluted by the fossil fuel carbon and this is also noticeable in the ocean carbon. This counters the false argument that the extra CO₂ entering the atmosphere is natural and is caused by warming of the oceans or the biosphere. If that were the case then the atmospheric concentration of oxygen would also be increasing and that is not occurring. In fact, the atmospheric oxygen content is reducing slightly in accordance with the amount of the gas required to burn the fossil fuels.

Over the last thirty-one years the correlation between surface temperature and CO₂ concentration is shown in Figure 8.

 

 

Figure 8 A plot of global temperature anomalies against the Mauna Loa CO₂ concentrations for the 1979-2008 period

The correlation coefficient is 0.64 and the slope of 0.0077°C increase of temperature for every 1 ppmv increase in CO₂ concentration is remarkably similar to that expected from the IPCC formula for forcing:

ΔF = 5.35 ln(c₂/c₁) for any two CO₂ concentrations, c₁ and c₂, c₂ > c₁

The forcing originating from an increase of CO₂ concentration from 385 to 386 ppmv is 0.0139 W m^-2 and this translates to a temperature increase of 0.0139/2 = 0.0069°C.

There are questions about whether such global factors are really relevant because of the observed asymmetry of warming in the 1979-2008 period. Another question to be resolved is that concerning the observed higher concentration of CO₂ in the atmosphere of the northern hemisphere and the observed higher rate of warming there. Is this significant and can it be properly explained. It certainly does not appear in the outputs of any of the GCMs. It seems that the excessive CO₂ production in the northern hemisphere is not the cause of the hemispherical asymmetry in temperature anomalies and that the latter is due to the greater thermostatic effect of the greater water area in the southern hemisphere.

Conclusions

From this limited data set of thirty-one years of temperature and CO₂ data it would seem reasonable to conclude that the observed warming, although asymmetrically distributed, is that expected from the straightforward forcing formula of the IPCC and seems to eliminate any exaggerations that they regard as important. If indeed the forcing formula has any respectability the expected forcing and consequent warming amounts to 2.675 ln (570/385) = 1.05°C if we can find enough fossil fuel to produce a CO₂ concentration of 570 ppmv, the latter being twice that of the pre-industrial era. A possible difficulty is that the asymmetric warming, with warming being almost entirely restricted to the northern hemisphere that region could experience a temperature increase of considerably more, maybe twice as much, than 1.05°C. But, as ever, extrapolation of graphs is a very doubtful exercise!