UPDATED – see below
Monckton provides these slides for discussion along with commentary related to his recent post on CO2 residence time – Anthony
There is about one molecule of 13C in every 100 molecules of CO2, the great majority being 12C. As CO2 concentration increases, the fraction of 13C in the atmosphere decreases – the alleged smoking gun, fingerprint or signature of anthropogenic emission: for the CO2 added by anthropogenic emissions is leaner in 13C than the atmosphere.
However, anthropogenic CO2 emissions of order 5 Gte yr–1 are two orders of magnitude smaller than natural sources and sinks of order 150 5 Gte yr–1. If some of the natural sources are also leaner in CO2 than the atmosphere, as many are, all bets are off. The decline in atmospheric CO2 may not be of anthropogenic origin after all. In truth, only one component in the CO2 budget is known with any certainty: human emission.
If the natural sources and sinks that represent 96% of the annual CO2 budget change, we do not have the observational capacity to know. However, we do not care, because what is relevant is net emission from all sources and sinks, natural as well as anthropogenic. Net emission is the sum of all sources of CO2 over a given period minus the sum of all CO2 sinks over that period, and is proportional to the growth rate in atmospheric CO2 over the period. The net emission rate controls how quickly global CO2 concentration increases.
CO2 is emitted and absorbed at the surface. In the atmosphere it is inert. It is thus well mixed, but recent observations have shown small variations in concentration, greatest in the unindustrial tropics. Since the variations in CO2 concentration are small, a record from any station will be a good guide to global CO2 concentration. The longest record is from Mauna Loa, dating back to March 1958.
The annual net emission or CO2 increment, a small residual between emissions and absorptions from all sources which averages 1.5 µatm, varies with emission and absorption, sometimes rising >100% against the mean trend, sometimes falling close to zero. Variation in human emission, at only 1 or 2% a year, is thus uncorrelated with changes in net emission, which are independent of it.
Though anthropogenic emissions increase monotonically, natural variations caused by Pinatubo (cooling) and the great el Niño (warming) are visibly stochastic. Annual changes in net CO2 emission (green, above) track surface conditions (blue: temperature and soil moisture together) with a correlation of 0.93 (0.8 for temperature alone), but surface conditions are anti-correlated with δ13C (red: below).
The circulation-dependent naturally-caused component in atmospheric CO2 concentration (blue above), derived solely from temperature and soil moisture changes, coincides with the total CO2 concentration (green). Also, the naturally-caused component in δ13C coincides with observed δ13C (below).
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The naturally-caused component in CO2 (above: satellite temperature record in blue, CRU surface record in gray), here dependent solely on temperature, tracks not only measured but also ice-proxy concentration, though there is a ~10 µatm discrepancy in the ice-proxy era. In the models, projected temperature change (below: blue) responds near-linearly to CO2 concentration change (green).
In the real world, however, there is a poor correlation between stochastically-varying temperature change (above: blue) and monotonically-increasing CO2 concentration change (green). However, the CO2 concentration response to the time-integral of temperature (below: blue dotted line) very closely tracks the measured changes in CO2 concentration, suggesting the possibility that the former may cause the latter.
Summary
Man’s CO2 emissions are two orders of magnitude less than the natural sources and sinks of CO2. Our emissions are not the main driver of temperature change. It is the other way about.
Professor Salby’s opponents say net annual CO2 growth now at ~2 μatm yr–1 is about half of manmade emissions that should have added 4 μatm yr–1 to the air, so that natural sinks must be outweighing natural sources at present, albeit only by 2 μatm yr–1, or little more than 1% of the 150 μatm yr–1 natural CO2 exchanges in the system.
However, Fourier analysis over all sufficiently data-resolved timescales ≥2 years shows that the large variability in the annual net CO2 emission from all sources is heavily dependent upon the time-integral of absolute global mean surface temperature. CO2 concentration change is largely a consequence, not a cause, of natural temperature change.
The sharp Pinatubo-driven cooling of 1991-2 and the sharp Great-el-Nino-driven warming of 1997-8, just six years later, demonstrate the large temperature-dependence of the highly-variable annual increments in CO2 concentration. This stochastic variability is uncorrelated with the near-monotonic increase in anthropogenic CO2 emissions. Absence of correlation necessarily implies absence of causation.
Though correlation between anthropogenic emissions and annual variability in net emissions from all sources is poor, there is a close and inferentially causative correlation between variable surface conditions (chiefly temperature, with a small contribution from soil moisture) and variability in net annual CO2 emission.
Given the substantial variability of net emission and of surface temperature, the small fraction of total annual CO2 exchanges represented by that net emission, and the demonstration that on all relevant timescales the time-integral of temperature change determines CO2 concentration change to a high correlation, a continuing stasis or even a naturally-occurring fall in global mean surface temperature may yet cause net emission to be replaced by net uptake, so that CO2 concentration could cease to increase and might even decline notwithstanding our continuing emissions.
Natural temperature change and variability in soil moisture, not anthropogenic emission, is the chief driver of changes in CO2 concentration. These changes may act as a feedback contributing some warming but are not its principal cause.
