How much carbon can be emitted in total?
The Copenhagen Accord agreed that global mean warming should be kept below 2°C above pre-industrial times (1.2°C above today's temperature) in order to avoid 'dangerous interference with the climate system'. How can we relate this 'safety limit' to our everyday lives, our choices for the future, and in particular to the development of the Alberta Oil Sands? Lets consider the numbers. In order to have a 66% chance of keeping warming below 2°C, future carbon emissions must remain below 0.59 trillion (T) tonnes (t) of carbon1
(2.2 trillion tonnes of CO2
). That is the total, cumulative carbon emissions over the next several thousands years must remain below 0.59 Tt. If we divide this number by the current population of earth, we find that in order to remain below 2°C, each person must emit less than 85 tonnes of carbon3
. I call this the 'allowable cumulative per capita carbon footprint' compatible with less than 2°C warming.
Current carbon footprints in the 2°C framework
Carbon Footprints for +2°C
The green circle illustrates the current maximum cumulative per capita carbon emissions compatible with keeping global mean warming below 2°C. The red circle shows the cumulative lifetime per capita carbon footprint of the average Canadian. The blue circle shows the average Chinese lifetime cumulative per capita carbon footprint.
Canadians currently have a carbon footprint of about 4.5 tonnes carbon per person per year (CDIAC, 2008
), or roughly 360 tonnes of carbon per average Canadian over their lives. (Numbers are similar, but slightly higher for Americans according to CDIAC). China currently has a per capita carbon footprint of 1.4 tonnes per year
(roughly 100 tC per average Chinese lifetime). Africans by contrast have an average per capita footprint of 0.32 tonnes
carbon per person per year. The global average annual per capita carbon footprint is 1.3 tonnes
carbon (or around 89 tonnes carbon over the average global lifetime of 67 years).
As we can see, these numbers exceed the 85 tonnes per person limit that is required to keep warming below 2°C. For the current global population (±7 billion), emitting at today's rates (1.3 tC/person/year), it would take about 60 years to emit 0.59 TtC and to push warming over 2°C above pre-industrial. A growing population, together with increasing per-capita emissions will shorten that period, perhaps significantly (e.g. see Figure 1 in Rogelj et al.). In fact, the situation is even more challenging, because the 0.59 TtC emissions cap for 2°C does not apply simply to the lifespan of the current global population, but rather is the limit for carbon emissions over the next 500 years at least (due to carbon's long residence time in the atmosphere1,2 - read below).
Carbon footprints of the Alberta oil sands and other global resources
Potential Oil Sands Carbon Footprints
The green circle illustrates the current maximum cumulative per capita carbon emissions compatible with keeping global mean warming below 2°C. The red circle shows the per capita carbon footprint that would result from the current populations of the USA and Canada utilizing the Alberta oil sands proven reserves. The blue circle shows the per capita carbon footprint that would be achieved by the current Chinese population by fully utilizing the proven oil sands reserve. The green-circle shows the limit for all emissions, but the red and blue circles show only oil-sands related emissions, and do not include emissions from other sources such as coal burning.
If the current populations of the USA and Canada burnt the 'economically viable' proven oil-sands reserve (170 billion barrels), they would achieve a per capita carbon footprint of 64 tonnes3
. This number does not include other sources of carbon emissions, such as coal fired power stations, natural gas usage, conventional crude oil usage, etc, etc. Thus if the populations of the USA and Canada were to extensively utilize the Alberta oil-sands proven reserve, it would almost certainly be incompatible with doing a globally equal share (85 tC) in keeping warming below 2°C. For comparison, the current Chinese population would achieve a cumulative per capita carbon footprint of 16 tonnes, by utilizing the entire Alberta oil sands proven reserve. This is below the 85 tC 'equal share', but of course does not include other emissions sources. These figures should be borne in mind before committing to large scale, long term oil-sands infrastructure projects such as the Keystone XL and Northern Gateway pipelines.
“the locking in of future emissions due to infrastructure investments represent a serious setback to our hopes of limiting the global rise in temperature to no more than 2° Celsius. ”
Dr. Faith Birol, IEA Chief Economist.
In general, building new large-scale infrastructure which commits society to long-term fossil-fuel usage is not consistent with keeping warming below 2°C, regardless of the particular fossil-fuel resource4. To prevent warming exceeding that limit, there will have to be a rapid, large scale transition to renewable energy sources. Indeed, if growing global energy demands are instead met using fossil fuels, the level of carbon footprints and the associated warming could be massive3. In general, a +4°C world is quite possible this century. So society faces a clear choice: a) continued fossil fuel-usage and large scale warming or b) transition towards renewable energy to stabilize the climate.
In fact, to ultimately stabilize the climate will require near zero emissions2, and to limit warming within 2° or so degrees, there will have to be an immediate, rapid decrease in emissions from today's levels towards zero, or even below5. What should these emissions reductions look like nationally?
National emissions targets and historical responsibility
How the required rapid decreases in carbon emissions should be distributed among nations is obviously a contentious political issue, as evidenced by tough negotiations at the recent UNFCCC COP 17.
We may think of the atmosphere as a common resource to humanity. We share the atmospheric common not only with other humans alive today, but also with all the generations that preceded us, and future generations that will follow us.
Now, if we agree the limit to anthropogenic warming should be less than 2°C, we can then calculate the total carbon emissions that are allowed since pre-industrial times (around 1.3 TtC6). We can think of this emissions quota as the total amount of 'atmospheric carbon real estate' available to humanity. How this atmospheric real estate should be divided amongst humanity in space and time is as I said debatable.
However, in the past, the West (or global North if you will), has used up the lion's share of atmospheric carbon real-estate. This is well illustrated by James Hansen's plot of cumulative emissions since pre-industrial times. There is no mistaking the fact that the global North (USA + Canada + W.Europe) bears most of the responsibility for the current anthropogenic carbon content of the atmosphere. China, India and the Global South have contributed a much smaller fraction of the current atmospheric carbon burden. This becomes even clearer if one considers cumulative historical emissions on a per capita basis, in which case Canada, Europe and the USA have contributed massively more to the current problem than China, India and the global South. Therefore its clear that Canada and the rest of the developed world should be taking responsibility, and leading efforts to reduce emissions.
The global North bears most of the responsibility for the current anthropogenic carbon content of the atmosphere.
If it was hoped to ultimately achieve a globally equal per-capita sharing of the carbon space in the atmospheric common, developed countries will have to use a smaller than average piece of the future emissions space; while developing countries are allowed to use a greater portion, to make up for the historical imbalance. Indeed, developing countries require this extra emissions space in order to have any hope of attaining a decent standard of living7.
One popular per-capita equity-based system for assigning emissions obligations is the 'contraction and convergence' (c&c) framework. However c&c does not make any differentiation of emissions reduction obligations based on national capacity. Thus for example, Kazakhstan and Belgium, who each emitted 3.5 tC/capita in 2005 have similar obligations under the c&c framework, which does not make sense given Belgium's much greater capacity to adapt7. The Greenhouse Development Rights framework developed by Baer et al.7, takes historical responsibility and capacity into account. This system therefore takes cognizance of poor countries need to develop, while still assigning them responsibility based on in-country capacity, thus bringing China, India and the developing world into the emissions reduction framework in an equitable way.
There are significant practical and political challenges to the actual transition to a low-carbon society. Even in the ideal case where developed countries do take the lead, the developing countries will have to leap-frog over fossil-fuel based technology directly to renewables, and aspire to greater energy efficiency in order to achieve development without significantly increasing their carbon footprints. Either way, the atmospheric carbon space below 2°C is a non-renewable resource which is being rapidly depleted.
- Zickfeld, K., Eby, M. Mathews, H.D. & Weaver, A.J. (2009), Setting cumulative emissions targets to reduce the risk of dangerous climate change, Proc. Natl. Acad Sci. USA 106. 16129-16134.
- Matthews, H. D., and K. Caldeira (2008), Stabilizing climate requires near-zero emissions, Geophys. Res. Lett., 35, doi:10.1029/2007GL032388.
- Swart, N.C. and Weaver, A.J. (in press), The Alberta Oil-Sands and Climate, Nature Clim. Change, .
- Davis, S.J., Caldeira, K. & Matthews, H.D. (2010), Future CO2 Emissions and Climate Change from Existing Energy Infrastructure, Science 10. 1330-1333. [DOI:10.1126/science.1188566]
- Arora, V.K. et al. (2011), Carbon emission limits required to satisfy future representative concentration pathways of greenhouse gases, Geophys. Res. Lett. 38, doi:10.1029/2010GL046270
- Mathews, H.D., Gillet, N.P., Stott, P.A. & Zickfeld, K., (2009) The proportionality of global warming to cumulative carbon emissions, Nature 459, 829-832
- Baer, P., Fieldman, G., Athanasiou, T. & Kartha, S. (2008), Greenhouse Development Rights: towards an equitable framework for global climate policy, Cambridge Review of International Affairs 21, 649-669.
See our commentary appearing soon in Nature Climate Change (publications)