Total Words = 3682
Shipping Pallets and Greenhouse Gas Emissions: Life Cycle Analysis Among
Different Pallet Types
Jefferson Coxa and Steven P. Hamburgb
aJefferson
bSteven
Cox, Box 1977 Brown University, Providence, RI 02912
P. Hamburg, Ittleson Associate Professor, Center for Environmental Studies, PO Box
1943 Brown University, Providence, RI 02912, Tel: 401 255 2216, Fax: 401 863 2700,
Steven_Hamburg@brown.edu. Current Position: Chief Scientist Environmental Defense Fund,
18 Tremont St. Boston, MA, Shamburg@edf.org
ABSTRACT
The environmental impact of pallet material type has not previously been assessed in
terms of greenhouse gas emissions. Since there are about 2 billion pallets in circulation in the
United States and 450 million new pallets constructed each year, the choice of pallet type and
disposal method presents a significant opportunity to lower the carbon intensity of supply chains.
This study compared the life-cycle greenhouse gas emissions associated with the manufacture,
transport and end-use of four major pallet types that meet the Grocery Manufacturers’
Association (GMA) specification, the largest single segment of the pallet market. Lifetime
carbon emissions are estimated at 3.3 million metric tons CO2 equivalents per year (mmtCO2e/y)
for nail-based wood, 0.9 mmtCO2e/y for doweled wood, 13 mmtCO2e/y for high-density
polyethylene plastic and 21 mmtCO2e/y for aluminum pallets, if all GMA pallets were of a single
type. Given the current domination of the GMA market by nailed pallets, these findings suggest

Corresponding Author
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that pallet choice and handling can reduce or increase emissions enormously; an industry wide
shift in pallet type could result in a decrease in greenhouse gas emissions on par with emissions
from about one million U.S. households. Pallet reuse can greatly reduce emissions associated
with pallet use, thus offering a real opportunity to mitigate the environmental externalities. With
greenhouse gas emission credits priced at $25 for every metric ton of avoided CO2 equivalent
emissions, pallet selection and effective reuse could represent untapped income of $330 million
annually.
Keywords: greenhouse gas emissions, carbon, pallets, life cycle analysis, emissions
credits
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INTRODUCTION
As concern about climate change grows, so does interest in understanding the greenhouse
gas emissions associated with different sectors of the economy and the opportunities for
mitigation. There is growing interest in the U.S. Congress to establish a cap on greenhouse gas
emissions, something that has been accomplished sectorally in the European Union, Australia,
and regionally in the United States [1]. There are increasing efforts to foster transparency
through disclosure of corporate greenhouse gas emissions e.g. Carbon Disclosure Project.
Organizations, including retail leaders such as Wal-Mart, are increasingly requiring suppliers to
submit plans for reducing their emissions. Up until now there has been limited inclusion of
pallets in the analysis of carbon emissions, with the exception of single use versus reusable
pallets. In the low-carbon economy that is rapidly gaining traction, the ability to reduce
greenhouse gas emissions will have an increasing role in defining the profitability of for-profit
entities. The ability to effectively navigate this paradigm shift is and will be determined by an
entity’s ability to understand and control greenhouse gas emissions.
In 2000, about 450 million shipping pallets were produced in the United States with 1.9
billion in circulation [2]. To construct these pallets, about 100 million cubic meters of softwood
lumber and 4.3 million cubic meters of hardwood lumber were consumed [3]. In 1995, the last
year for which data is available, the wood used in pallets represented an astounding 38 percent of
the annual U.S. hardwood lumber production and 6 percent of U.S. softwood lumber production
[4]. In addition, the pallet industry consumed 18.7 million square meters of oriented strand
board and softwood plywood in that same year [3].
The 2,700 enterprises in the pallet-manufacturing sector generated $6.5 billion dollars in
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revenue in 2006. The pallet industry is largely domestic, with imports only claiming a 3 percent
share of the domestic market. The southeastern United States and Great Lakes regions are the
centers of pallet manufacturing with half of the industry's establishments [5].
While there are many different pallet types used in the United States, the Grocery
Manufacturers Association (GMA) 48 inches by 40 inches (100 centimeters by 120 centimeters)
specification pallet represents 30 percent of the 450 million pallets produced each year. There are
570 to 600 million GMA pallets in use in the United States at any one time, largely for the
transport of foods, beverages and other consumer goods [2]. GMA pallets are designed for reuse
and thus each is carried greater distances over their lifetime than are single-use pallets.
Nailed wooden pallets accounted for over 95 percent of the GMA pallet market in 2007.
Nailed pallets are constructed of softwood, with hardwood edges and support boards held
together with approximately 120 steel nails. They weigh 32 kilograms on average. There are
three additional types of GMA pallets: wood-dowel pallets, plastic pallets, and aluminum pallets.
The wooden dowel pallet represents less than 1 percent of the GMA pallet market. This pallet
uses softwood joined with hardwood dowels held with phenol-resorcinol-formaldehyde glue and
weighs an average of 25 kilograms. Plastic pallets, which weigh 22 kilograms, represent 2
percent of new pallet production [6]. Plastic pallets are made of high-density polyethylene
(HDPE), a common and recyclable plastic, and steel rebar, which is integrated into the pallet for
structural integrity. Aluminum pallets, which also comprise less than 1 percent of the GMA
pallet market, are made of marine-grade extruded aluminum and weigh an average of 16
kilograms.
The objective of our analysis is to understand how using different pallet types impacts
greenhouse gas emissions in the United States. If we are going to have any hope of meeting the
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challenge of mitigating climate change, we must know how our choices at every level of the
economy influence greenhouse gas emissions. In the following analysis we focus on pallets
because, although they are ubiquitous in the United States, with an average of seven per person,
there is almost no public information on the effects of pallet type on greenhouse gas emissions.
LIFE CYCLE ANALYSIS
We conducted a life-cycle analysis of the manufacture, use, and disposal of each of the
four GMA pallet types (nailed, doweled, plastic and aluminum). We calculated the greenhouse
gas emissions, in million metric tons of CO2 equivalents per year (mmtCO2e/y), associated with
each pallet type, assuming each in turn was used to meet 100 percent of market demand. The
CO2 equivalent describes the quantity of CO2 with an equivalent global warming potential as a
given mixture of greenhouse gases. For example, a single methane (CH4) molecule has the same
global warming potential as 21 molecules of CO2, while nitrous oxide (N2O) is the same as 310
CO2 molecules [7].
Manufacture
Insert Table 1 Approximately Here
Insert Table 2 Approximately Here
Embodied energy is the total primary energy consumed during the lifetime of a product,
energy needed to get it from cradle to grave [8]. Since pallet manufacturers do not release data
on their energy use, we used literature-derived material characteristics to calculate the total
embodied energy in each pallet type. Table 1 shows the embodied energy of pallet component
materials, and Table 2 displays the embodied energy of each pallet. The embodied energy of
pallet materials is highest for aluminum and lowest for wood.
The amount of greenhouse gases emitted by each pallet also depends on their lifespan.
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Table 3 shows the yearly market demand for the manufacture of new pallets. The manufacture of
a sustainable supply of the different pallet types will result in the release of: 6.6 mmtCO2e/y
from nailed pallets (requiring 135 million pallets constructed every year), 1.2 mmtCO2e/y from
dowel pallets (40 million pallets constructed per year), 11 mmtCO2e/y from HDPE pallets (40
million pallets constructed per year), and 22 mmtCO2e/y released from aluminum pallets (40
million pallets constructed per year).
Insert Table 3 Approximately Here
Use
The key characteristic that influences carbon emissions associated with a pallets use is
weight. Lighter pallets require less fuel to transport, thereby reducing carbon emissions.
Based on a floor space of 2.6 meters by 1.5 meters, semi tractor-trailers can carry around
24 pallets [9]. For every liter of diesel fuel burned, 2.7 kg CO2 equivalent is emitted [7]. The
weight of the pallets in a loaded tractor-trailer varies from 760 to 380 kg/trailer depending on
pallet type. The annual emissions created by moving each pallet type under our assumptions
range from a high of 5 mmtCO2e/yr for nailed pallets to a low of 2.5 mmtCO2e/yr for aluminum
as a result of their respective weights.
End-Use
What happens to a pallet at the end of its useful life has a large impact on its carbon
footprint. Table 4 displays the end of life options for each type of pallet. Pallets can be rebuilt,
recycled, burned for energy or put in a landfill. These options for end-of-life handling and their
environmental impacts are largely dependent on (1) the material from which they are constructed
and (2) the degree to which reuse/recycling options are employed. In our analysis, we have used
a set of assumptions for the end-of-life programs that we feel are attainable for pallet
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manufacturers and consumers.
The nailed pallet may be burned as fuel to displace oil, disposed of in a landfill or rebuilt.
When a wooden pallet becomes unusable, repairing it reduces material costs by extending the
lifespan of some of the wood. The portion of a pallet’s wooden boards that are cracked, warped
or shredded are not useful for building another pallet and may be sent to a landfill or used as fuel.
If the unsalvageable wood in each pallet were sent to a landfill, greenhouse gases would be
emitted by anaerobic decomposition. Alternatively, with a biomass end-use program, spent
wooden pallets could be burned in a boiler to produce usable energy: process heat or electricity.
The plastic pallet may be separated into steel and HDPE and recycled. Using recycled
materials reduced the total embodied energy and carbon emissions. Recycling HDPE causes it to
lose some of its structural integrity [10] and thus it needs to be mixed with virgin resins when
used for the construction of new pallets.
Like the nailed pallet, a spent dowel pallet can be burned as fuel to displace oil, disposed
of in a landfill or rebuilt. The dowel pallet is made entirely out of wood, being held together with
resorcinol adhesive, and thus, when it reaches the end of its life, it can be more easily chipped
and burned as a fuel than can the nailed pallets. When sent to a landfill, the decomposition of the
organic components of the dowel pallets result in greenhouse gas emissions.
Aluminum pallets, made of two extruded aluminum surfaces with polypropylene
connecting spacers, can also be recycled. Recycled polypropylene, like HDPE, has a lower
structural integrity than virgin material; consequently, it is subject to the same recycling
limitations as HDPE. Aluminum is highly recyclable as it can be melted and reformed without
loosing any structural integrity.
Insert Table 4 Approximately Here
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Increased public awareness of the environmental implications of solid waste production
has resulted in pallet manufacturers marketing end-use programs (e.g. recycling, efficient rental
systems and sustainable forestry practices); however, data on the scale and effectiveness of these
programs is unavailable. Thus, we have carried out two calculations, one based on the current
situation, where we assume all GMA pallets are sent to landfill and a second where we assume a
more aggressive reuse strategy based on the recycling rates listed above.
Under the current situation, where all unusable pallets are sent to landfill, greenhouse gas
emissions vary widely among pallet types, from a high of 24 mmtCO2e/yr for the aluminum
pallet to a low of 5.2 mmt CO2e/y for the doweled pallets. Table 5 shows the carbon emissions
or reductions associated with the use of each pallet type.
Insert Table 5 Approximately Here
If the aggressive reuse strategy outlined above were implemented and applied to the
entire market, the range of emissions would drop markedly. The HDPE pallet would have the
highest emissions at 11 mmtCO2e/y and the doweled pallets would have the lowest with 4.5
mmtCO2e/y. For these calculations, it is important to note that no recycled aluminum would be
used in the first generation of aluminum pallets. Even if aluminum pallet manufacturers
purchased recycled aluminum explicitly, they would be displacing a portion that would likely be
filled by virgin material. If we assume greenhouse gas emissions credits are priced at $25 per
metric ton of CO2, the value of the marginal emissions reduction realized by implementing the
aggressive end-use program would be between $18 and $330 million dollars, depending on pallet
type. This income stream could potentially be tapped if there are cap and trade regimes
established under climate change mitigation legislation. The cost of implementation of these
reuse/recycle scenarios would be offset by income associated with greenhouse gas emissions
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credits, leaving no net cost of implementation.
CONCLUSION
Pallets vary widely in their environmental impacts and in particular their carbon
footprint. The differences in the associated carbon emissions among the pallet types could be
equivalent to the emissions from 1 million U.S. homes. The pallet industry could reduce U.S.
greenhouse gas emissions by about 0.3 percent by selecting pallets and end-of-life strategies with
smaller carbon footprints. While this may seem like a small number, it could easily represent a
billion dollars worth of carbon credits in the cap and trade systems currently being discussed in
the U.S. Congress. Given that pallets represent an important part of the supply chain of most
products, managing the carbon emissions associated with their manufacturing and use represents
an important opportunity for mitigating climate change.
We hope that our analysis will encourage manufacturers to become more transparent with
respect to their practices, and in so doing, allow a more complete discussion of the advantages of
each type of pallet. We encourage purchasers of pallets to demand full carbon accounting and
transparency, as is being done in other supply chains across the economy. Based on our analysis
there are important differences in the greenhouse gas emissions associated with pallets
constructed of different materials. Current marketing claims of some pallet manufacturers could
easily lead purchasers to spurious conclusions about their environmental impacts. We believe
that a thorough examination of the implications of pallet type, as begun here, suggests that the
negative environmental externalities associated with pallet materials that have high-embodied
energy make them a poor overall choice for most applications. As is clearly evident from our
analysis, a more aggressive program of reuse/recycling is key to reducing greenhouse gas
emissions associated with pallet use. The bottom line is that opportunities for reducing carbon
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emissions associated with the pallet industry are plentiful, economically advantageous and will
help this industry stay competitive in the emerging low-carbon economy.
ACKNOWLEDGEMENTS
The author would like to thank Nathaniel Manning and Nora Buckman of Brown
University for help in the initial research phases. Information and support was provided by: Mike
Miller, President and CEO of Miller Dowel Company who suggested the project initially, Dr.
Ralph Rupert, Director, Center for Unit Load Design at Virginia Polytechnic Institute and State
University; Dr. Dan Tingley, founder of Wood Research and Development, LLC; Dr. Jack
Davis, Reynolds Metals Professor and Dean of the Virginia Tech College of Architecture and
Urban Studies; Tiger Aster, President of Toro Pallets LLC; and Dr. H.W. Cox, Founder and
President, Advanced Oxidation Technologies LLC. Special thanks to Ruth Yanai for critical
comments on an early draft of this manuscript.
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