It is the primary cry of the deniers and the false sceptics – “There is no definitive link between atmospheric carbon dioxide and global temperature.” (I leave the genuine, scientific sceptics out – those who play a constructive role in challenging the science.)
Last Friday, the new edition of Nature contained an article on just that missing link. The carbon-climate ratio, or CCR, has formally entered the climate science lexicon.
The researchers used 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.(frog’s emphasis)
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. Professor Matthews and colleagues say 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.
Professor Mathews says that the 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. The report concludes that if we want to restrict global warming to no more than two 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.
Our findings allow people to make a robust estimate of their contribution to global warming based simply on total carbon dioxide emissions.
To the part time trolls on this blog who always think that what they do makes no difference, I say here is your metric. Here you can calculate what your personal contribution to global warming is. There is no more excuse for free-riding or bludging, which are the favourite policies of those who say New Zealand should do nothing.
This is from the abstract of the June 11 edition of Nature:
The global temperature response to increasing atmospheric CO2 is often quantified by metrics such as equilibrium climate sensitivity and transient climate response. 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:
- the warming per unit CO2 emitted does not depend on the background CO2 concentration;
- the total allowable emissions for climate stabilization do not depend on the timing of those emissions; and
- the temperature response to a pulse of CO2 is approximately constant on timescales of decades to centuries.
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 6C per trillion tonnes of carbon (Tt C) emitted (5th to 95th percentiles), consistent with twenty-first-century CCR values simulated by climate–carbon models.
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.
This is very important news with huge implications for policy, both here and abroad. If I find time, I’ll calculate what New Zealand’s contribution is to global warming, based on our greenhouse gas inventory published last month.