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Developed nations lead in cutting per capita CO2 emissions while developing nations lead in cutting warming by methane, soot, trop ozone



The incremental warming influence during the 21st century from potentially controllable 21st century emissions will be roughly half due to CO2 emissions and half due to emissions of methane, precursors of tropospheric ozone, and other non-CO2 GHGs. Because of the CO2 perturbation's long persistence time, cutting CO2 emissions is essential to limiting long-term climate change. Because of their short lifetimes, cutting emissions of short-lived species is the only way to slow the rate of warming over the next few decades (see UNEP 2011 report). While sulfate-induced cooling and black-carbon induced warming influences have roughly canceled in the past, cutting CO2 emissions will very likely lead to sharp reductions in SO2 emissions, and so in sulfate cooling, necessitating that black carbon emissions be cut comparably if an additional strong warming influence is to be avoided.

Using the 100-year Global Warming Potential to combine emissions of these different forcing agents into the single CO2e measure of emissions and treating only the Kyoto basket of greenhouse gases fails to deal with all of the warming (and reduced cooling) agents while at the same time obscuring possibilities for negotiating an agreement that would be effective and equitable given the different situations and contributions of different nations to global climate change.

Recognizing the different situations and responsibilities that exist, an effective and equitable agreement to limit climate change that would involve commitment to comparable efforts through differentiated actions can be envisioned. In particular:

a. Developed nations commit to rapidly reducing their per capita CO2 and other GHG and aerosol emissions, demonstrating that modern economies can prosper without unduly impacting the climate, while

b. Developing nations commit to actions to reduce emissions of short-lived gases, actions that would have many co-benefits, and also to not exceeding declining developed nation per capita emissions.


Category of the Action

Integrated action plan for the world as a whole

What actions do you propose?

Past negotiations between developed and developing nations have been like stalled labor negotiations--neither group of nations wants to commit to doing anything fearing that the other group of nations will not respond in a reciprocal fashion. With a nation's total CO2e emissions being the only metric used as an indication of commitment (sometimes augmented by a nation's contributions to deforestation and biospheric CO2 release), the negotiating space is very constrained and little progress has been made as heated discussions of equity, effectiveness, and comparative effort have dominated meeting time and put off agreement on moving forward.

Over the past several years, the shortcomings of relying on CO2e as a metric have become more obvious. As it is being used, this metric does not encompass all of climate forcing agents and relying on the 100-year Global Warming Potential (GWP-100) obscures the different timings of the different influences; scientifically, its use has many shortcomings, as indicated in the recent IPCC report. Diplomatically, use of CO2e also is very constraining, obscuring the potential for nations in different stages of development to contribute to limiting global warming in ways that are tailored to their particular situations and roles in contributing to climate change. Even though CO2e has become the norm, and the use of GWP-100 is so engrained it is often not even mentioned, its use, both because of its scientific and diplomatic shortcomings, appears to be a major impediment to negotiating a practical, effective, and equitable agreement and needs to be discontinued.

Simulations described in the UNEP 2011 report on the relative roles of black carbon, tropospheric ozone and methane in global warming indicate that a reasonably aggressive mitigation program has the potential to cut the projected warming between the present and 2050 in half and could, coupled with a reasonably aggressive CO2 mitigation effort, limit overall global warming to of order 2-2.5 C above the preindustrial baseline. From a scientific point of view, it is clear that undertaking either of these approaches alone would not lead to an effective limitation of global warming--both steps must be taken, a result that is simply not apparent when relying solely on the CO2e-based analyses.

An earlier, more general recognition of the dual nature of this challenge led to a proposal that would take advantage of the different primary responsibilities for emissions of CO2 and of short-lived species (MacCracken, 2008). To break the apparent deadlock between the developed nations (Annex 1) and developing (non-Annex 1) nations about moving beyond the Kyoto Protocol, the proposal was that:

a. Developed nations commit to taking aggressive, quantifiable actions to limit their GHG emissions, which for most nations are primarily CO2 emissions although emissions of all warming agents must be cut, with the goal of greatly reducing their per capita emissions and demonstrating that modern economies can prosper with no or very low effects on the environment. Without demonstrating this, the moral basis for developed nations to insist on actions by developing nations is greatly undermined and also, even if developing nation emissions magically went to zero, the present emissions pathway of developed nations would cause the 2 C global temperature goal to be exceeded during the second half of the 21st century, increasing the likelihood of exceeding critical temperature thresholds and tipping points.

b. Developing nations commit, in a first phase of their efforts, to aggressive, quantifiable steps to cut emissions of short-lived species, especially methane, black carbon and the precursors of tropospheric ozone. Many of these nations already have initial efforts to limit emissions of these substances in order to improve air quality, improve energy efficiency, improve visibility, and more--there are many co-benefits to cutting emissions of these substances in addition to limiting climate change. As part of the negotiating process, the developing nations need to commit to quantitative cutbacks and the emissions of these warming agents and, as important, to be recognized for the comparable contribution and effort to limiting climate change that these mitigation efforts involve. In the first phase, in recognition of the need for energy to lift their citizens out of poverty, no hard limit would be placed on their CO2 emissions, although a voluntary commitment to improving energy intensity would be encouraged.

Recognizing that the overall growth in CO2 emissions from developing nations must be limited, the agreement would require that in phase 2, as development and fossil fuel energy use of individual nations increases, they would commit to keeping their per capita CO2 (and other GHG) emissions to less than the declining value in developed nations.

This proposal, potential nuances, and its effectiveness are described more fully in Moore and MacCracken (2009).


Where will these actions be taken?

The proposed action is the negotiation of an international agreement. It would involve the participation of all those nations involved in the Conference of the Parties negotiations under the UN Framework Convention on Climate Change. Supporting documentation for the proposal would need to be prepared by UNEP and UNFCCC staff.

Who will take these actions?

The key actors would be those involved in the negotiations of the international agreements.

A key audience would be those in the particular nations who view it as particularly important that all parties to the negotiations be playing comparable actions to limit climate change. What needs to be clearly explained is that:

(a) even were emissions in developing nations to magically go to zero tomorrow and indefinitely into the future, the present energy path of the developed nations will cause the global average temperature to rise to above 2 C in the latter half of the 21st century--that is, the energy choices of the billion people in the developed nations can alone cause 'dangerous anthropogenic interference' with the climate; indeed the past emissions from these nations have been the primary contributor to the very disturbing and growing impacts that are already evident; and 

(b) even were emissions in developed nations to magically go to zero tomorrow and indefinitely into the future, the present energy path of the developing nations would also cause the global average temperature to rise to above 2 C in the latter half of the 21st century--that is, the energy path intended to lift the six billion (and increasing) people in the developing would out of poverty will cause changes in climate that recent World Bank reports make clear will have devastating effects on economies and well-being of those living in presently developing nations.

What all parties need to understand is that we are all in this together, that the issue is imminent, and that action now by all is required. Recognizing that, however, there are issues of equity and fairness that must be considered, and this can be done if an approach based on best and comparable efforts across differentiated approaches is made the underlying principle of the negotiations.

What are key benefits?

The key benefit of adopting this approach is the potential for an effective and workable agreement to which all nations can be a party and that has the potential of actually limiting the increase in global average temperature to about 2-2.5 C above its preindustrial baseline. Approaches that are based on nations trying to cut their CO2e emissions give every indication that they will be unable to adequately limit the rise in global average temperature if they can be agreed to at all. There is no guarantee of success, but no other approach seems as likely to be as workable.

Aside from the many benefits of limiting the pace of climate change, the other key benefits are the many co-benefits that would come from forcefully moving to reduce emissions of the short-lived species, particularly the improvements in public health, air and water quality, energy efficiency, visibility, and more.

What are the proposal’s costs?

While there are upfront costs to aggressively cutting back emissions of CO2 and of cutting back emissions of short-lived species, there are an increasing number of technologies for accomplishing these cutbacks that, based on direct costs alone, would limit the effective costs over periods of a decade or so to very low amounts, and that, if indirect co-benefits are accounted for, even in the absence of the many direct and indirect benefits of limiting climate change, would be beneficial or quite limited.

One important potential reduction in costs of the effort could result if the methane concentration could be taken down to below its 1990 level, which is often assumed to be the baseline. Given the high GWP of methane, on the 100-year timescale, but even more on the 20-year timescale, sharply cutting back methane emissions would have the benefit of, essentially, allowing for a slightly higher value of the CO2 concentration that would be indicated in analyses based on the CO2e metric.

Time line

With negotiations about meaningful reductions in emissions having now dragged on unproductively for over two decades, adopting the proposed strategic approach to reconciling the differing views, interests and perspectives of the developed and developing nations has the potential to become the basis for an agreement that could be reached over the next few years. As an agreement that would have each of the groups of nations focused most intensely on what they most need to do, and indeed are already starting to pursue (although too slowly and without adequately recognizing the value of the efforts underway), the proposed strategy has the potential to really invigorate the global effort to limit climate change, increasing the possibility that the rise in global average temperature could be kept below 'dangerous anthropogenic interference with the climate' and brought down after it peaks to levels that would more convincingly be recognized as likely to be safe.


Underneath the type of general strategy proposed here there would be hundreds and hundreds of types of actions, different in each nation, that are needed. With fossil fuels, energy has appeared to be a global commodity with a global market. In the future, as renewables take over, the international market will shrink and each nation will be doing more and more to generate its own energy (of course, electric networks and biofuels may well keep the international market going, but more likely on a regional scale). Thus, the issue is not which of the many proposals might be best, but to recognize that each of hundreds may well have roles to play in one or more locations. Thus, it really does not make sense to get into extensive listing of particularly proposals---we need everything there is everywhere it can be done productively and as soon as possible.

How do these sub-proposals fit together?

Explanation of model inputs

First, model simulations of the proposed cutbacks have already been done, in quite extensive detail (see, e.g., Shindell et al., 2012 and Jackson, 2009) and in a more schematic form (Moore and MacCracken, 2009). What is new about this proposal is in how to use what has been demonstrated and understood about the different actions to be taken to create the bridge needed to get to a practical political agreement. This is a key challenge that won't be overcome by just listing a whole gamut of actions--the key is who has to do what and when, and an overarching philosophy is needed to overcome the present approach in which no group wants to step forward for fear that the other group will not have to undertake comparable efforts.

Second, the EnROADS model is simply not set up to do the type of analysis that needs to be done. In relying, or so it appears, on CO2e and the 100-year Global Warming Potential and in focusing almost exclusively on the general energy sector, it is totally obscured actions in other sectors and seems to misleadingly treat the front loading effect of methane emissions on global warming. Basically, by setting up the model as it has been set up, the options for really taking action are obscured, making the task of avoiding what would be considered dangerous warming far more difficult than it is (it is still difficult, it is just that using GWP-100 and CO2e makes it virtually impossible).


Jackson, S., 2009: Parallel Pursuit of Near-Term and Long-Term Climate Mitigation, Science 326, 526-527.

MacCracken, M. C., 2008: Prospects for Future Climate Change and the Reasons for Early Action, Journal of the Air and Waste Management Association, 58, 735-786. DOI: 10.3155/1047-3289.58.6.735

MacCracken, M. C., 2010: Moderating climate change by limiting emissions of both short- and long-lived greenhouse gases, pp. 225-241 in Proceedings of the International Seminars on Nuclear War and Planetary Emergencies: 42nd Session, Erice, Sicily, Italy, 20-23 August 2009, edited by R. Ragaini, The Science and Culture Series: Nuclear Strategy and Peace Technology, World Scientific, Singapore.

Moore, F. C., and M. C. MacCracken, 2009: Lifetime-leveraging: An approach to achieving international agreement and effective climate protection using mitigation of short-lived greenhouse gases, International Journal of Climate Change Strategies and Management 1, 42-62. doi:10.1108/17568690910934390

Moore, F. M., and M. C. MacCracken, 2011: Short-lived greenhouse gases and climate fairness, pp. 145-166 in chapter 7 in China and Global Climate Change: Ethics, Responsibility and Environmental Policy, edited by P. G. Harris, Policy Press, Bristol, UK, 256 pp.

Shindell, D., et al., 2012: Simultaneously Mitigating Near-Term Climate Change and Improving Human Health and Food Security, Science 335, 183-189; DOI: 10.1126/science.1210026.

United Nations Environment Programme, 2011: Integrated Assessment of Black Carbon and Tropospheric Ozone, Nairobi, 2011.