Science 13 December 2013:
Vol. 342 no. 6164 pp. 1323-1324
Policy Forum

What Role for Short-Lived Climate Pollutants in Mitigation Policy?

J. K. Shoemaker, D. P. Schrag, M. J. Molina, V. Ramanathan | 6 Comments

Parallel strategies must focus on long- and short-lived pollutants, but not at the cost of reducing pressure for action on CO2.

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Shoemaker et al. (1) raise the important issue of comparing benefits of reducing emissions of “short-lived” black carbon (BC) and methane (CH4) with “long-lived” carbon dioxide (CO2). They believe trading between CO2 and CH4 “should be discouraged” and compare three scenarios: one reducing CO2 emissions through 2050 by 20%, a second reducing BC by 80% and CH4 by 40%, and a third reducing all three pollutants by the same percentages. Obviously, the third scenario results in the greatest mitigation. However, the scenarios are not normalized by the cost of achieving the specified reductions, and the third (recommended) scenario presumably costs as much as the other two combined. The most efficient way to distribute funds among options is to have them compete with each other through a market mechanism, rather than a central authority setting targets for each gas or mitigation type, much as production targets were decreed in the former Soviet economy. While markets can be tweaked and channeled to maximize non-climate benefits (and avoid perverse impacts), exchangeability is essential. CH4 emissions from tropical dams add to controversies over carbon credit for hydropower (2-4). Reducing methane emission has rapid benefits for slowing temperature increase (essential to avoid surpassing the 2°C threshold now agreed as “dangerous”). The weight giving to methane must reflect the importance for human society of this key role (5, 6). PHILIP M. FEARNSIDE National Institute for Research in Amazonia (INPA), Manaus, Amazonas, Brazil. E-mail:


1. J.K. Shoemaker et al., Science 342, 1323 (2013). doi: 10.1126/science.1240162.

2. P.M. Fearnside, Mitig Adapt. Strat. Global Change 18, 691. (2012). doi:10.1007/s11027-012-9382-6.

3. P.M. Fearnside, Carbon Manage. 4, 681. (2013). doi: 10.4155/CMT.13.57.

4. P.M. Fearnside, S. Pueyo, Nature Climate Change 2, 382. (2012). doi: 10.1038/nclimate1540.

5. P.M. Fearnside, Environ. Conserv. 24, 64 (1997). doi: 10.1017/S0376892997000118.

6. P.M. Fearnside, Ecolog. Econ. 41, 21 (2002). doi: 10.1016/S0921-8009(02)00004-6.

Submitted on Thu, 07/10/2014 - 16:00

Affiliations for preceding comment:

(a) Michael C. MacCracken, Climate Institute, Washington DC 20006; (b) Frances C. Moore, Stanford University, Emmett Interdisciplinary Program in Environment and Resources, Stanford CA 94305;

References for preceding comment: 1. J. K. Shoemaker et al., Science 342,1323 (2013). 2. J. Hansen, Sci. Amer., 290 (3), 68 (2004). 3. Scientific Expert Group on Climate Change, Confronting Climate Change: Avoiding the Unmanageable and Managing the Unavoidable, report for United Nations Commission on Sustainable Development (Sigma Xi and the United Nations Foundation, Washington, DC, 2007). 4. M. C. MacCracken, J. Air & Waste Mgmt. Assoc. 58, 735 (2008), with additional publications at 5. A. Steiner, (2009); 6. F. C. Moore, M. C. MacCracken, Intl. J. Clim. Chg. Strategies & Mgmt. 1, 42 (2009) 7. M. C. MacCracken, World Best Practices, Asia-Pacific Edition, 6(3), 48 (2010) ( 8. United Nations Environment Programme and World Meteorological Organization, Integrated Assessment of Black Carbon and Tropospheric Ozone” (UNEP, Nairobi, 2011). 9. Potsdam Institute for Climate Impact Research and Climate Analytics, “Turn Down the Heat: Why a 4°C Warmer World Must be Avoided” (World Bank, Washington DC, 2012) 10. Potsdam Institute for Climate Impact Research and Climate Analytics, “Turn Down the Heat: Climate Extremes, Regional Impacts and the Case for Resilience“ (World Bank, Washington DC, 2013) 11. F. C. Moore, M.C. MacCracken, in China’s Responsibility for Climate Change: Ethics, Fairness and Environmental Policy (The Policy Press, Bristol, UK, 2011).

Submitted on Mon, 06/09/2014 - 14:21

Submitted for publication Jan. 6, 2014; returned by AAAS June 5, 2014. References and affiliations in separate comment:

To the Editor:

Shoemaker et al. (1) join previous authors (2-8) in advocating mitigation of both short-lived climate forcers (SCFs) and long-lived greenhouse gases (LLGHGs) but fail to discuss how such a strategy might be effected.

On the one hand, reducing emissions of the SCFs that also contribute to air pollution is already becoming a priority in many middle-income countries (MICs) faced with poor air quality and associated public health problems. On the other hand, there is a long-standing impasse in international negotiations. The developing nations point to their poverty and low per-capita CO2 emissions as reasons their economic growth should not be legally constrained by emission caps, while developed countries point to large and growing absolute emissions from MICs as reasons why mitigation by developed nations alone would be ineffective. The result has been non-binding pledges clearly inadequate for preventing devastating consequences from climate change (9-10).

Since CO2 emissions are critical for determining peak and equilibrium warming, achieving significant CO2 mitigation is essential for seriously addressing climate change. The relevant political question is thus how to leverage the distinct characteristics of SCFs to generate agreement on LLGHGs (4-7). An international agreement committing developed nations to early, ambitious cuts in LLGHG emissions and MICs to slower near-term growth (and eventual long-term cuts) in CO2 emissions while implementing aggressive cuts in SCFs would be effective, politically feasible, and beneficial to the standard-of-living for all. Far from reducing CO2 mitigation, this strategy would leverage the many co-benefits of SCF mitigation to politically enable CO2 mitigation. Our earlier work demonstrated that such an approach could keep warming by 2100 to ~2°C while being consistent with the principles of common but differentiated responsibility and capacity that underpin the UNFCCC (6,11).

While SCF mitigation alone is clearly inadequate, focusing solely on limiting emissions of LLGHGs has achieved very little since the 1992 UNFCCC agreement. SCF strategies that ignore the potential to leverage progress on CO2 mitigation would miss a unique opportunity (6).

Michael C. MacCracken(a) and Frances C. Moore(b)

References and affiliations included in following comment.

Submitted on Mon, 06/09/2014 - 14:17

The figure in this article reflects the temperature change depending on years starting 2000, rising constantly (“Reference”, blue line). This however is in contrast to the measured overall temperature being about constant up to 2012, see e.g. IPPC-report 2013, Box 11.1, Figure 1. This discrepancy between the real world and the model suggests that the latter seems to be rather flawed. A theory like the model describing the climate change ought to reflect the reality otherwise it is deemed not being valid and ought to be rejected or at least revised. Obviously the theory does not reflect the influence of various factors correctly. Thus, using it to describe the effect of short lived climate pollutants must be questioned, too. It should be noted that also in said IPCC-report this discrepancy between the observed global mean temperature and the average over the ensemble of simulations, i.e. theoretical models, exists.

Submitted on Wed, 01/29/2014 - 04:57

Shoemaker et al. (1) weigh short versus long-term trade-offs between reducing emissions of CO2 versus short-lived climate pollutants to minimize future warming impacts. Supply-side approaches amount to reshuffling deck chairs if they overlook demand-side solutions. CO2 cannot be reduced to safe levels in time to avoid serious long-term impacts unless CO2 increasing sinks are increased while simultaneously decreasing sources (2,3).

Nearly half the excess atmosphere CO2 came from soil carbon loss before fossil fuel combustion (4,5). Soil holds around 4 times more carbon than atmosphere or vegetation, and could hold more (5). The dynamic time response spectrum of CO2 sources and sinks shows the fastest way to decrease CO2 is to increase photosynthesis and biomass storage as tropical soil carbon (6), which could resolve the problem in decades, but CO2 source reductions alone take centuries to millennia to have an effect so impacts will be far worse (6).

Transferring carbon from atmosphere to soil would greatly increase soil productivity, biomass, groundwater resources, and reduce temperature through increased evapotranspiration. Effective methods to greatly increase soil carbon by intensifying natural biogeochemical recycling (7,8) work in agricultural lands (9), reforesting degraded land (10), pastures, and forests.

“Down To Earth” underground grass-roots Geotherapy solutions (11) to global warming are ignored by policy makers’ focus on source reductions and geo-engineering. They need to look at the other side of the coin, implementing solutions that can work in time to make a difference by removing carbon from the atmosphere, where it does the most harm, and putting it in the soil, where it does the most good. The answer lies at our feet.

1. Shoemaker, Schrag, Molina, & Ramanathan, 2013, Science, 342:1323-1324 2. Goreau, 1987, Nature, 328:581-582 3. Goreau, 1990, Ambio, 19:230-236 4. Ruddiman, 2005, Princeton 5. Houghton, 2003, 473-513 in Holland & Turekian, Treatise on Geochemistry, Vol. 8, Elsevier 6. Goreau, 1995, 65-79 in Pernetta, Leemans, Elder, & Humphrey, Impacts of Climate Change on Ecosystems and Species: Environmental Context, IUCN 7. Lal, 2011, Food Policy, 36:S33-S39 8. Lehmann, & Joseph, 2009, Routledge 9. Woolf, Amonette, Street-Perrot, Lehmann, & Joseph, 2010, Nature Comm. 1:56 doi:10.1038/ncomms1053 10. Myers, & Goreau, 1991, Climatic Change, 19:215-225 11. Goreau, Larson, Campe (Eds), 2014 in press, CRC Press

Submitted on Thu, 01/09/2014 - 11:44

J. K. Shoemaker et al note two remarkable opinions. The first one is they do not believe that real decisions about health policies and climate policies are made through an interconnected market (1). However, it is not objective to ignore the function of market in the process of making decisions about health and climate policies. The main reasons are: first, currently emission-reduction policy in the energy and industrial sectors of developed countries has commonly been approached through market-based incentive structures, such as cap-and-trade or tax-and-subsidy programs (2). Second, according to REDD+ approach proposed by the United Nations Framework Convention on Climate Change (UNFCCC)(3), developed country donors, corporations, NGOs, and individuals will compensate developing countries for emissions reductions, including through market mechanisms (4, 5). Third, the economic benefits of some natural resources that can reduce emissions in regional or national levels needs market actions. For instance, preventing mangrove loss has the potential of reducing global emissions for a cost of roughly $4 to $10 ton−1CO2 (6). The Amazon protected areas network represents a cost of US$147±53 billion (net present value) for Brazil in climate change mitigation (7). The second one is J.K Shoemaker et al. recognize that compromises may be required to achieve political goals (1). However, the outcome through compromises between nations is limited. From Kyoto Protocol in 1998 to Bali Action Plan in 2007, from Copenhagen Accord in 2009 to Cancun agreement in 2010, from Durban Package Outcomes in 2011 until to Warsaw UNFCCC in 2013 (8), althrough all of our human beings are still discussing about climate problems, the final outcome is limited extremely. The key reason is most of them are not willing to make a concession. The authors advocate that giving developing countries some form of “credit” for reductions in SLCPs may be important to broaden participation in international climate agreements. However, we have to consider its feasibility. In fact, from what we have discussed above we can see that the solution of climate problems needs the effective integration of market mechanism and political institutional arrangement at different levels (9). International climate agreement should be an bilateral negotiation, more important is it needs positive cooperation to break through the difficulties, rather than just depending comprimises each other(10,11). Reference...

Submitted on Wed, 01/08/2014 - 00:22