From my unscientific understanding, if the latest findings of Damon Matthews, a professor in Concordia University's Department of Geography, Planning and the Environment bear out, then the public understanding of AGW will have it's smoking gun. Matthews and his colleagues claim to have found a direct relationship between carbon dioxide emissions and global warming.
The latest edition of
Nature, June 11, 2009, published the findings from a combination of global climate models and historical climate data to show that there is a simple linear relationship between total cumulative emissions and global temperature change.
Science Daily reported:
Until now, it has been difficult to estimate how much climate will warm in response to a given carbon dioxide emissions scenario because of the complex interactions between human emissions, carbon sinks, atmospheric concentrations and temperature change. Matthews and colleagues show that despite these uncertainties, each emission of carbon dioxide results in the same global temperature increase, regardless of when or over what period of time the emission occurs.
These findings mean that we can now say: if you emit that tonne of carbon dioxide, it will lead to 0.0000000000015 degrees of global temperature change. If we want to restrict global warming to no more than 2 degrees, we must restrict total carbon emissions – from now until forever – to little more than half a trillion tonnes of carbon, or about as much again as we have emitted since the beginning of the industrial revolution.
"Most people understand that carbon dioxide emissions lead to global warming," says Matthews, "but it is much harder to grasp the complexities of what goes on in between these two end points. Our findings allow people to make a robust estimate of their contribution to global warming based simply on total carbon dioxide emissions."
Here's the Abstract:
The proportionality of global warming to cumulative carbon emissions
H. Damon Matthews1, Nathan P. Gillett2, Peter A. Stott3 & Kirsten Zickfeld2
Nature 459, 829-832 (11 June 2009) | doi:10.1038/nature08047
Abstract: The global temperature response to increasing atmospheric CO2 is often quantified by metrics such as equilibrium climate sensitivity and transient climate response1. These approaches, however, do not account for carbon cycle feedbacks and therefore do not fully represent the net response of the Earth system to anthropogenic CO2 emissions. Climate–carbon modelling experiments have shown that: (1) the warming per unit CO2 emitted does not depend on the background CO2 concentration2; (2) the total allowable emissions for climate stabilization do not depend on the timing of those emissions3, 4, 5; and (3) the temperature response to a pulse of CO2 is approximately constant on timescales of decades to centuries3, 6, 7, 8. Here we generalize these results and show that the carbon–climate response (CCR), defined as the ratio of temperature change to cumulative carbon emissions, is approximately independent of both the atmospheric CO2 concentration and its rate of change on these timescales. From observational constraints, we estimate CCR to be in the range 1.0–2.1 °C per trillion tonnes of carbon (Tt C) emitted (5th to 95th percentiles), consistent with twenty-first-century CCR values simulated by climate–carbon models. Uncertainty in land-use CO2 emissions and aerosol forcing, however, means that higher observationally constrained values cannot be excluded. The CCR, when evaluated from climate–carbon models under idealized conditions, represents a simple yet robust metric for comparing models, which aggregates both climate feedbacks and carbon cycle feedbacks. CCR is also likely to be a useful concept for climate change mitigation and policy; by combining the uncertainties associated with climate sensitivity, carbon sinks and climate–carbon feedbacks into a single quantity, the CCR allows CO2-induced global mean temperature change to be inferred directly from cumulative carbon emissions.
More about Damon Matthews' work:
Chasing climate change Global Warning Climate Change Energy
