Quote from jem:
nitro... you like stats.. you will immediately see this guy is very credible.
Ironically, the first 11 minutes of the talk provide all the components required to show beyond reasonable doubt that anthropogenic emissions are responsible for 100% of the observed increase in atmospheric CO2 and that natural sources do not play a major role. At 08:39, Prof. Salby correctly states that
"What is relevant is net emissions, net collected from all sources and sinks, human and natual, that is what ultimately controls atmospheric CO2"
This is then supported by a slide (at 8:58) containing an equation that will be familiar to those that have followed the discussion of earlier claims that the rise in atmospheric CO2 is a natural phenomenon at SkS, for example my rebuttal of Prof. Essenhigh's residence time argument.
This is known as the mass balance equation, and it simply states that as the carbon cycle obeys the principle of conservation of mass, the annual increase in atmospheric CO2 is equal to the difference between total emissions from all sources (both natural and anthropogenic) and the total uptake from all sinks (natural and anthropogenic, although the anthropogenic sink is essentially zero as we are not yet performing significant amounts of carbon sequestration).
For convenience, we can re-write Prof. Salby's mass balance equation in the form
C' = Ea + En - Un,
where Ea represents annual carbon emissions from anthropogenic sources (fossil fuel use and land use change), En represents the carbon emissions from all natural sources (the oceans, soil respiration, volcanos etc.) and Un represent the uptake of carbon by all natural carbon sinks (oceans, photosynthesis, etc.). C' represents the net emissions rate, which as Prof. Salby says is approximately equal to growth rate of global mean atmospheric CO2.
The problem is then that we don't know the values of En and Un with any real certainty as our knowledge of the natural carbon cycle is limited. However, we do have good knowledge of anthropogenic emissions, Ea, as Prof. Salby says (at 7:53)
"In truth only one component of the CO2 budget is known with any certainty, human emissions, implicitly through records of extraction - how much coal and oil are dug up"
There are also good records of emissions due to land use changes as well. We also have reliable observations of the growth rate of CO2 in the atmosphere, as Prof. Salby says (10:35)
"That [CO2 being well mixed in the atmosphere] is a good thing because it means that local values are good approximations of the global average, which in turn provides a record of net global emissions. In fact we have a long record of CO2 from only one site in the free atmosphere, Mauna Loa Hawaii. The local record from Mauna Loa therefore approximates the global mean, which through its growth rate chronicles the history of net global emissions, collectively from all sources, human and natural."
In other words we can reliably work out the net emission rate from the Mauna Loa CO2 record by computing the annual growth in atmospheric CO2, i.e. C'.
This allows us to find out something interesting about the natural carbon cycle: The mass balance equation can be rearranged to give an estimate of the difference between annual emissions from all natural sources and annual natural uptake by all natural sinks.
En - Un = C' - Ea
While we don't know the values of En or Un, the difference between them is constrained by conservation of mass to be the same as the difference between C' and Ea, which we do know! More importantly if we knew the right hand side of this equation was negative, then we would know that the left hand side must also be negative, so whatever their actual values, Un > En.
O.K., so if we look at the data (for details, see Cawley, 2011), we find that the annual rise in atmospheric CO2 has been less than anthropogenic emisssions every year for at least the last fifty. We therefore can also be sure that the natural environment has been a net carbon sink, taking in more carbon than it has emitted, every year for the last fifty. As the natural environment is known to be a net carbon sink, far from being the cause of the observed rise in atmospheric CO2, it has been actively opposing it!
Key Point: It isn't the variability (the general up and down wiggliness) in net emissions that gives rise to the long term trend, it is the mean value of the net emissions, and the value of the correlation does not depend in any way on the mean value. Therefore the correlation with net global emission tells you very little about the cause of the long term trend.
http://www.skepticalscience.com/salby_correlation_conundrum.html