Prof. Ross McKitrick from Guelph University has published with Mark Strazicic and Junsoo Lee an interesting paper on the flat trend of per capita CO2 emissions from fossil fuels: Stationarity of Global per capita CO2 Emissions (2007). He shows an essential flat trend line during the last 30 years, and suggests, that what developing countries emit more will be compensated by higher energy efficiency in the more developed ones, which will be rejoined in the near future by the first. He concludes that most of the IPCC emission scenarios in the SRES are way too pessimistic, and that the scenarios with the lowest emission rates should be considered as the most probable.
I remade some graphs showing the situation, and using the data from CDIAC:
This first graph shows the yearly CO2 emissions (in GtC; 1GtC = (1/3.67) GtCO2) in blue and the yearly per capita emissions in red (in tC), from 1959 to 2006. Contrary to the much hyped exponential increase emissions rose nearly in a linear manner, at about 0.106 GtC per year or 1 GtC per decade. The next graph shows that indeed per capita emissions are more or less stable since 1975 (the trend is even slightly negative) at 1.15 tC per year.
Now a recurrent question is: what is the influence of these emissions on the atmospheric CO2 concentration (more correct: the CO2 mixing ratio)?
This graph shows that despite natural variations the atmospheric CO2 concentration increases linearly with the yearly emissions; 1 GtC additional emitted carbon would push up CO2 levels by about 13 ppm.
Or the other way around: to push up CO2 concentration by 1 ppm, the world has to emit an additional 1/13 GtC = 0.077 GtC = 77 MtC = 77 000 000 tC
A world population reaching 9.2 billion in 2050 (and possibly culminating at that number) would emit 9.2*1.15 = 10.6 GtC per year, compared to a calculated 6.5*1.15 = 7.5 GtC in 2006. This would push up atmospheric CO2 levels by (10.6 – 7.5)*13 = 40 ppm, reaching 420 ppm.
Compared to the 380 ppm concentration of 2006 the 420 ppm would correspond to a supplementary GHG forcing of 5.36*ln(420/380) = 0.54 Wm-2 or a probable warming of 0.25*0.54 = 0.13 °C; the factor 0.25 being the non-feedback gain G defined by dT0 = G*dQ, where dT0 and dQ are the increases in temperature and forcing. (see for instance the Lindzen & Choi paper: On the determination of climate feedbacks from the ERBE data, 2009). Lindzen/Choi suggest a negative feedback f = -1.1, so the warming would be dT = dT0/(1-f) = 0.13/2 = 0.07 °C. If we stick to the non-feedback projection, the warming would be a meager 0.13 °C!
The IPCC extravagant warming increases are possible only by hypothesing big positive feedbacks, contrary to what observational data suggest.
These simple, even naive projections suggest that strict and brutal emission reduction policies are pointless in respect to anthropogenic global warming.
update 14Mar10 18:43 UTC:
I found the 2009 data on Wikipedia (CDIAC stops at 2006):
global emissions by all countries: 7.74 GtC
world population: 6.8 billion
per capita emission: 1.13 tC per year
So these data do not invalidate the 1.15 tC found above.
Sorry, these Wikipedia data are 2006 CDIAC !
I found the 2008 world emissions (probably without LULC etc…) on SCRIBD; the per capita number is 1.11, so the impressive positive trend from 2002 to 2006 seems broken. Assuming a constant per capita 1.15 tC does not err on the “wrong” size!