Everybody agrees that we have to reverse global warming and that we should lower carbon emissions, but the trick is who should do it and how much should each one be held responsible for. The issue is very similar to having a pothole on your regular route to work. Everybody agrees that the pothole needs to be fixed, but nobody gets down to fix it. Why should I? In a local community, there is elected government that is responsible to take care of that kind of stuff. But what do we do in a global context? Who should fix the rising temperatures?
Bear in mind, fixing the pothole costs money, and so does fixing our carbon emissions. No nation wants to foot the bill! Talking about bill, how much should the bill be for each of the nations? Should we levy it as a "global warming tax" across all nations?
If it is a tax, should it be a flat tax based on the population of each of the countries or should be based on GDP or carbon emissions intensity? Most of the existing approaches looked at this problem of target attribution at the national level. This problem was very similar to you going to the restaurant with a bunch of your friends, and you order some dish for $10, and end up paying $50 when the dinner bill is split amongst all your friends, because others had ordered dishes that averaged $60 per person. The innovative approach proposed by Princeton Environment Institute (PMI) researchers looks at the "individuals at the dinner table" rather than the group / nation as a whole, in terms of attributing carbon emissions reduction target.
The universally adopted United Nations Framework for Convention on Climate Change (UNFCCC) viewed the world in two groups for the purposes of reducing carbon emissions - developed countries were urged to lead the charge, and, developing nations were supposed to follow the lead set by the developed nations based on common but differentiated responsibilities. The framework did not propose any timeline for developing countries to execute that effort. There was no consensus on what the carbon emissions reduction targets should be and hence not a whole lot has been accomplished till now. Now in 2011, there are signs that a consensus is emerging with reasonable / low targets, which will need both the developed and the developing nations to work together to reach achieve those targets. Also the world has changed since 1992 (when the framework was first proposed), now developing nations contribute to 50% of the global carbon emissions, which is significantly higher than their share of ~30% two decades back.
One of the key challenges in distributing the carbon emission reduction targets has been generating consensus among different nations with regards to approach for identifying targets.
The approach, for personal carbon footprint, proposed by the PMI researchers, attributes national targets for fossil fuel CO2 emissions based on a fairness principle built on common but differentiated responsibilities of individuals, rather than nations. And it goes beyond the per capita attribution, and focuses on personal carbon footprint of high-emitting individuals across all nations in the world.
Their approach, for computing personal carbon footprint, combines practicality, fairness, and can be accomplished with readily available data. The computation is based on the consumption patterns of the individuals regardless of which country they live in, and the data that they base this computation on is a mix of per capita income distributions and national carbon emission intensities. The key in this approach is the threshold assigned for personal carbon footprint, and any individual that goes beyond the threshold will be counted in the sum total that will be used to define the responsibility / target for emissions reduction for that country. For example, if the personal carbon footprint cap was set at 1 ton CO2/yr per person, based on MGD (Millennium Development Goals), then the emissions of all high-emitters (those with emissions higher than 1 tCO2/yr) will be added up to arrive at the national target for CO2 reduction. Based on current understanding, by 2030 annual CO2 emissions of the World will be at 43 GtCO2 / yr, and the experts have agreed that more sustainable annual emissions target for 2030 is 30 GtCO2 / yr. In order to reduce 2030 emissions by 13 GtCO2, the personal carbon footprint cap should be set at 10.8 tCO2/yr per person. Current projections show that there will be about 1.13 billion people with emissions higher than that cap.
The big advantage of this approach is that, countries with more number of high-CO2-emitting individuals will have higher CO2 emissions reduction targets and those countries with fewer rich individuals will have zero or minimal CO2 emissions reduction targets. This will make it a more "fair" process in terms of attribution of reduction targets. Once the countries agree to an overall reduction target (current at 13 GtCO2 / yr for 2030), then the individual country target can be relatively easily computed and attributed in a fair manner, without burdening the developing / poorer nations.
This approach focuses only on fossil fuel CO2 emissions. Biospheric CO2, other greenhouse gases, and aerosols, (all which impact the environment) are not addressed in this approach as there is no strong correlation between personal expenditures and national carbon intensities. Some of the other factors that this approach does not fully address are:
The key to mobilizing the nations to work together to address global warming is to generate consensus on who should pay how much of the "global warming tax". Personal carbon footprint approach proposed by PMI researchers has the potential to generate that consensus, so that nations can start the actual work of reducing emissions!! Long way to go, but this is a good start.