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WASTE, RECYCLING & CLIMATE CHANGE
Frank Ackerman, Director or the Research and Policy Division of GDAE, Tufts University, Medford MA, USA
Abstract
Waste management has at least five types of impacts on climate change, attributable to (1) landfill methane emissions, (2) reduction in industrial energy use and emissions due to recycling and waste reduction, (3) energy recovery from waste, (4) carbon sequestration in forests due to decreased demand for virgin paper, and (5) energy used in long-distance transport of waste. A recent U.S. EPA study provides estimates of overall per-ton greenhouse gas reductions due to recycling. Calculations using these estimates suggest that the U.S. could realize substantial greenhouse gas reductions through increased recycling, particularly of paper.
Key Words: Waste management, climate change, methane, landfills, recycling, sequestration.
Introduction
Discussion of the causes of climate change usually begins with energy consumption, as it should -- but too often ends there as well. It is certainly true that most anthropogenic emissions of greenhouse gases result from the combustion of fossil fuels. Yet it is important to look at the climate change impacts of other environmental concerns, such as waste management, for two reasons. First, there are some significant non-energy sources of greenhouse gases, including the emission of methane from landfills; and second, choices and policies in the realm of waste management have a surprisingly large effect on the ways in which we use energy.
Waste is not only a large contributor to the greenhouse problem; it is also an area where doing the right thing for the environment is politically popular. It is much easier to persuade most people to change the way they handle solid waste than, for example, to get them to drive sensibly small, fuel-efficient cars. Thus waste management is a promising area in which to pursue reduction in carbon emissions, and should be part of any comprehensive strategy for climate change mitigation.
In this paper I will present a framework for analysis of the greenhouse impacts of climate change, then offer some estimates of the size of the impacts and finally make approximate calculations of the importance of these impacts for the U.S. In view of the many uncertainties and approximations that must be made along the way, the numbers that I end up with are not reliable bases for policy making, but hopefully serve to demonstrate that there is something big enough to justify an analysis in greater detail and precision.
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Five Categories of Impacts
How does waste management affect greenhouse gas emissions? There are at least five categories of impacts to consider. The first and most obvious is landfill methane emissions. Estimates for the U.S. (EPA 1999a) suggest that landfill methane accounts for about 4% of all greenhouse emissions, measured in terms of global warming potential. On a global level the Intergovernmental Panel on Climate Change (IPCC) estimates that landfill methane accounts for 3% of all greenhouse emissions, but may account for 8-10% of all feasible near-term opportunities for emission reduction (IPCC 2001:14).
Most of the organic waste in landfills decays anaerobically, and most of the carbon is gradually released to the atmosphere, about half of it as carbon dioxide and half as methane. The latter is the problem: the same amount of carbon has a global warming potential 21 times greater if it is released as methane rather than carbon dioxide.
This impact is unmistakably caused by modern waste management. When waste ends up as litter, or in small, uncontrolled, uncompacted dumpsites, there are potentially severe problems of sanitation, public health, and aesthetics B but the decay of waste under these conditions is aerobic, releasing virtually all of its carbon as CO2 rather than methane. As low-income countries develop, they will increasingly move from open dumping of wastes to sanitary landfilling, implying that landfill methane emissions will be a growing problem worldwide in the future.
The other impacts are, for the most part, less visibly part of the waste management process. But they are still caused by the decisions we make about waste and materials.Most important is the fact that both recycling and waste reduction lead to decreased energy use and process emissions in industry. The IPCC estimates that primary (virgin material) production causes 40 times the greenhouse emissions of secondary (recycled material) production per ton of aluminum. For many other industrial materials, primary production emissions are 4 to 5 times as great as secondary emissions per ton. (IPCC 1996: 670)
Most of this savings reflects the change in industrial energy use. Extractive industries such as mining, and basic materials industries such as metal, paper, and plastics production, are the most energy-intensive branches of industry, using far more energy per dollar of output than later stages of manufacturing. For example, most of the energy required to make an automobile is used to extract raw materials from nature and process them into bulk industrial commodities; much less is used to shape the materials, fabricate car parts, and assemble them. Recycling of raw materials, or using less to begin with, reduces energy use and associated carbon emissions in the most energy-hungry branches of industry.
A third type of impact arises when energy recovery from waste displaces fossil fuel consumption. This can occur through incineration; through other energy recovery technologies such as pyrolysis; and through capture of landfill gas. Controlling landfill gas has a double benefit: landfill methane can be substituted for natural gas, a fossil fuel; and combustion converts methane to carbon dioxide, vastly reducing its greenhouse impact. For the same reason, even the simple technique of flaring landfill gas, i.e. burning it without capturing the resulting energy, is of great benefit from a climate change perspective Õ though burning the gas with energy capture is obviously a better idea.
At first glance, it is hard to see why there is a climate change benefit to burning waste paper in an incinerator instead of coal in a conventional power plant. Both combustion processes release CO2 into the air. However, paper comes from trees, which absorb CO2 from the atmosphere as they grow. Assuming sustainable forestry practices (a controversial assumption, but not one that will be pursued here), the emissions from burning paper will be balanced by the growth of new trees, leading to zero net emissions over the paper life cycle. This assumption is standard in climate change analyses. A parallel assumption can be made, perhaps less controversially, for incineration of other materials of recent biological origin, such as garden waste and food waste.
In contrast, fossil fuels are not renewable on any relevant time scale; their combustion does, therefore, lead to a net increase in atmospheric CO2. Among ordinary solid wastes, the same is true only for plastics, which are made from fossil fuels. So when a waste-to-energy facility substitutes for a fossil-fuel-burning power plant, the appropriate comparison is between the CO2 emissions from plastic wastes (only a fraction of the incinerator=s feedstock) and the emissions from all of the fossil fuel. There are longstanding debates over the environmental merits of incineration of paper, involving this and many other technical issues (see, for example, Blum et al. 1997 and Grieg-Gran et al. 1997).
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Varieties of Sequestration
A fourth category of impacts also depends on complex hypotheses about forestry and other environmental policies: paper recycling and reduction may have an effect on carbon sequestration in forests. Any decrease in the production of virgin paper means that fewer trees need to be cut down. Hence, depending on assumptions about other factors that affect forest practices, there may be more carbon left standing in the woods.
A recent U.S. EPA study of waste and climate change (EPA 1998a) employed an intricate series of forestry and paper industry models to estimate the sequestration effect. (I was a member of the large research team for that study, though I was not involved in the sequestration analysis.) The forestry models essentially showed that an increase in recycling or source reduction of paper leads immediately to decreased timber harvesting, implying an increase in the volume of wood standing in the forests. Forest owners will gradually respond by reducing their stocks of wood, either by planting less or by using their forests for other purposes. However, this adjustment is slow, due to the time lags involved in planting and growing trees; and even in the long run, the adjustment may be less than complete.
Other models and assumptions could lead to other conclusions. However, the EPA study (EPA 1998a) finds on the one hand that there are rather small energy savings due to paper recycling -- that is, the second impact category, as discussed above, is of relatively little importance in this case. On the other hand, it finds that the forest sequestration savings due to recycling or reduction are quite large. On this basis, it finds paper reduction or recycling to be far better than incineration from a climate change perspective.
There are other opportunities for carbon sequestration in waste management and materials use, though they are on a smaller scale than in forestry. Carbon can also be sequestered in wood buildings and furniture, and in paper products. All of us who have not gotten around to cleaning out old file drawers full of forgotten papers are doing our bit to sequester carbon at home and at work.
A final, paradoxical form of sequestration should be mentioned briefly. In this case, I confess that I remain puzzled by the work of my colleagues on parts of the U.S. EPA study. According to laboratory experiments done by one of the researchers, a noticeable fraction of the carbon in landfilled yard waste and newspaper is never released, but remains sequestered indefinitely in the landfill. The same experiments showed almost no sequestration for landfilled office paper and food waste. For newspaper, landfill sequestration is smaller than the forest sequestration that results from recycling; the best thing to do with newspaper, from a greenhouse perspective, is still to recycle it. For yard waste, there is no such alternative, so it is possible that net carbon emissions are somewhat lower when yard waste is landfilled rather than composted.
This result, which has surprised almost everyone, is based on only one set of laboratory experiments. It will be important to see whether it is confirmed by other researchers. (Unpublished research is currently exploring the possibility that land application of compost leads to increased carbon sequestration in soils, an effect which was omitted in EPA 1998a but should be included in the compost life cycle. With a credit for soil sequestration it is possible that composting will cause slightly lower greenhouse emissions than landfilling.) The effect is not large in any case; no version of the analysis suggests that much progress could be made in reducing greenhouse emissions by changing the management of yard waste. The analysis does, however, cast doubt on past assumptions that composting is a natural strategy for reducing carbon emissions.
The final impact category is energy required for transportation of waste materials. If recycled materials are transported far enough, the energy savings from recycling may be offset by the energy consumed in moving the materials. In a worst-case scenario, sending recycled glass by truck from Boston to Denver, about 3000 km, would undo most or all of the greenhouse benefits of recycling. The truck emissions for the journey would roughly negate the carbon reduction achieved in glass production. Note that this is a worst case: emissions are lower for long-distance freight transport by rail or by ship; and emission savings are lower for glass than for most other recycled materials. At the other extreme, recycling aluminum creates such huge per-ton savings in energy and greenhouse emissions that the effects of long-distance transport are insignificant by comparison.
The transportation effect can safely be ignored for recycling in most urban, industrial areas where distances to processing facilities are reasonably short. However, in low-density rural areas far from urban centers the need for long-distance shipping of recyclable materials reduces their environmental benefit, at least from a climate change perspective.
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Measuring the Impacts
How large are the greenhouse gas reductions achievable through waste management? Table 1 presents the estimates developed in the U.S. EPA study, for nine recyclable materials; Figure 1 displays the same information graphically. The table and graph show the change in emissions, relative to landfilling, for each material and each waste management option.
Table 1: Changes in greenhouse gas
emissions, relative to landfilling
Tonnes of CO2-equivalent emissions per tonne of material
|
| Material |
Waste Management Option |
|
Source Reduction |
Recycling |
Combustion |
| Newspaper |
-2.7 |
-2.5 |
0.0 |
| Office Paper |
-6.3 |
-5.4 |
-2.9 |
| Cardboard |
-3.3 |
-3.0 |
-0.9 |
| Aluminum Cans |
-12.0 |
-15.7 |
+0.1 |
| Steel Cans |
-3.4 |
-2.3 |
-2.0 |
| Glass |
-0.6 |
-0.4 |
0.0 |
| HDPE Containers |
-2.5 |
-1.5 |
+0.8 |
| LDPE Containers |
-3.6 |
-2.0 |
+0.8 |
| PET Containers |
-4.0 |
-2.5 |
+0.9 |
| Source: EPA 1998a, Exhibit
8-5, converted to metric tonnes of CO2-equivalent emissions per metric
tonne of material. Figures shown here are the differences between
emissions for landfilling and for each of the other waste management
options. The landfill scenario used as a baseline assumes that 54%
of landfills have methane capture systems, which are 75% efficient,
implying that an average of 40% of all landfill methane emissions
are captured. |
A number of important patterns can be seen in Table 1 and Figure 1. Almost all the numbers are negative (in the graph, most bars extend to the left of the zero line), indicating that almost everything is an improvement over landfilling from a climate change perspective. The only significantly positive entries in the table are for incineration of plastics, which gives rise to air emissions. In contrast, plastics are inert in landfills, and do not cause any emissions.
For this study, landfills were assumed to recover 40% of all methane, the ambitious new regulatory target (effective as of 2000) that may be above the actual U.S. average. With a lower rate of methane capture, landfilling of paper would look worse, and doing anything else with paper would look comparatively better.
The table shows that incineration is roughly as good as or better than landfilling for non-plastics, but is worse than recycling and source reduction for every material. The surprising climate change benefit from Acombustion@ of steel cans reflects the fact that incinerators recover and recycle much of the ferrous material they receive. Combustion of newspaper is no better than landfilling due to the assumption that landfilling of newspaper leads to long-term carbon sequestration. Without that assumption, landfilling newspaper would look worse, and all other newspaper options would look better.
Recycling of all nine materials leads to reduction in greenhouse gas emissions, relative to landfilling. The benefits per ton are greatest for aluminum and smallest for glass. Source reduction is even better than recycling, with the exception of aluminum. The explanation of this puzzle is that source reduction is assumed to replace the existing mix of virgin and recycled aluminum used in the U.S. today, while recycling is assumed to replace purely virgin material. Due to the large difference in energy intensity between virgin and recycled aluminum production, this means that the material being replaced is noticeably less energy-intensive for source reduction than for recycling.
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Three Recycling Scenarios
The numbers in Table 1 tell us the per-ton effect of recycling on greenhouse gas emissions (under American conditions and the numerous assumptions used in the study). These numbers can then be multiplied by the quantities of recycled material, in tons, to determine the total emission reductions attributable to recycling. Three sets of comparable data on recycling will be useful for the purposes of this calculation, all for 1996:
- The estimated U.S. average level of recycling
(EPA 1998b); and
- Recycling in Seattle, Washington and in
Bergen Country, New Jersey, two well-documented success stories of American
recycling (EPA 1999b).
Table 2 shows the levels of recycling of selected materials in these three areas; Figure 2 summarizes the extent of paper and non-paper recycling.
|
Table 2: Recycling of selected materials
in 1996, in kilograms per person |
|
U.S. average |
Seattle |
Bergen |
| Newspaper, misc. paper |
35 |
165 |
122 |
| Office/High Grade
Paper |
11 |
24 |
26 |
| Cardboard |
66 |
185 |
124 |
| Aluminum |
3.5 |
4.1 |
6.8 |
| Glass |
11 |
25 |
26 |
| Plastics |
3.6 |
2.7 |
12 |
| Ferrous |
15 |
10 |
32 |
| Sources: U.S. average (EPA
1998b); Seattle and Bergen Country (EPA 1999b). |
The next calculation simply consists of multiplying the numbers from Tables 1 and 2. Table 3 shows the reduction in greenhouse gas emissions due to recycling in each of the three cases, in kilograms of CO2-equivalent emissions per capita; Figure 3 again summarizes the impacts from paper and non-paper recycling. The total emission reduction is almost half a ton per person for the U.S. average, and more than a ton for both Seattle and Bergen County. Paper recycling accounts for more than three-fourths of the savings in all cases, and more than 90% in Seattle.
Table 3: Greenhouse gas emission
reduction per capita due to recycling, 1996
(kilograms of CO2-equivalent emissions per capita)
|
|
U.S. average |
Seattle |
Bergen |
| Newspaper, misc. paper |
86 |
413 |
304 |
| Office/High Grade
Paper |
59 |
128 |
143 |
| Cardboard |
199 |
556 |
371 |
| Aluminum |
55 |
64 |
108 |
| Glass |
4.3 |
10 |
11 |
| Plastics |
7.3 |
5.4 |
25 |
| Ferrous |
35 |
22 |
74 |
| Total |
446 |
1198 |
1034 |
| Paper as % of total |
77% |
92% |
79% |
| Sources: Recycling impacts
per tonne from Table 1 multiplied by quantities from Table 2. Newspaper
coefficient applied to miscellaneous paper; average of plastics products
used for plastics. |
The final calculation presents a further conjecture: how big would the impacts be if all 265 million Americans (the 1996 U.S. population) had recycled at these per capita rates? The answer is shown in Table 4, both in million tonnes of CO2-equivalent emissions, and finally as a percentage of U.S. greenhouse gas emissions.
The existing rate of recycling already saved 2% of nationwide emissions, relative to the baseline of landfilling all discards. If everyone achieved the Bergen County or Seattle recycling rates, an additional 2.7% - 3.5% of total emissions would be saved. These percentages may sound small. But recall that the Kyoto targets call for roughly 30% reduction in total emissions, relative to a Àbusiness as usual” scenario. Thus matching the best recycling programs nationwide could get us something like one-tenth of the way to compliance with the Kyoto Protocol.
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Conclusion
More research is needed to solidify the numerous assumptions used in this analysis. The scenarios presented here, with potential savings due to recycling ranging from 2% to 5.5% of national greenhouse gas emissions, are meant to illustrate the approximate magnitude of the effects of waste management, not to provide hard results for planning purposes. Among the crucial areas for further investigation are the actual rate of landfill methane capture, the impact of paper reduction and recycling on forest carbon sequestration, and the puzzling possibility of carbon sequestration in landfills. (Since this last puzzle is unresolved, no calculations have been included here for greenhouse impacts of composting.)
Yet despite these uncertainties, the effect of waste management choices on climate change is large enough that it is well worth studying in greater detail. Paper recycling, and the analysis of the paper life cycle, appear to be of particular importance. It is remarkable to think that we have the potential to achieve one-tenth of the Kyoto targets through an activity that already has widespread grassroots support. Although the data presented here are for the U.S., similar conclusions apply to other countries with similar waste streams, such as Australia and Canada. (For an earlier version of this analysis developed for Australia, see Ackerman 2000. ) The impact of waste on climate change is an important subject to pursue as we develop strategies for greenhouse gas reduction for the twenty-first century.
References
Frank Ackerman 2000. ÀWaste Management and Climate Change,” Local Environment 5 no. 2, 223-229.
Lauren Blum et al. 1997. ÀA Life-Cycle Approach to Purchasing and Using Environmentally Preferable Paper: A Summary of the Paper Task Force Report,” Journal of Industrial Ecology 1 no. 3, 15-46.
EPA (U.S. Environmental Protection Agency) 1999a. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-97 (EPA 236-R-99-003).
EPA 1999b. Cutting the Waste Stream in Half: Community Record-Setters Show How (EPA 530-R-99-013).
EPA 1998a. Greenhouse Gas Emissions from Management of Selected Materials in Municipal Solid Waste, (EPA 530-R-98-013).
EPA 1998b. Characterization of Municipal Solid Waste in the United States: 1997 Update (EPA 530-R-98-007).
Maryanne Grieg-Gran et al. 1997. ÀTowards a Sustainable Paper Cycle: A Summary,” Journal of Industrial Ecology 1 no. 3, 47-68.
IPCC (Intergovernmental Panel on Climate Change) 2001. Summary for Policy Makers of the IPCC WG III Third Assessment Report.
IPCC 1996. Climate Change 1995: Impacts, Adaptations and Mitigation of Climate Change(Cambridge University Press).
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