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Abstract
Carbon accounting and reporting will likely become necessary for various key
industrial sectors due to government regulations and policies. The U.S.
Environmental Protection Agency is in the process of finalizing the power-plant
carbon rules. Working towards a regional carbon trading scheme, the state of
California will soon require annual carbon emission reporting of compliance
that covers 85% emission sources and industry sectors. While the construction
industry has the third highest greenhouse gas (GHG) emissions among all US
industry sectors, emission estimates are dramatically different from
construction activities primarily due to the complexity of construction
activities and the lack of carbon accounting standards. This paper presents a
framework of carbon accounting for construction projects. The paper compares
existing enterprise carbon accounting standards and evaluates their
applicability at the project level. A life-cycle project carbon accounting
protocol is developed that follows a bottom-up approach and covers emissions
from site-preparation, material manufacture, on-site construction, waste
management, operation and environmental mitigation. With detailed discussion on
calculation methods for example emission sources, the protocol provides a
guideline for construction professionals to identify possible alternatives in
terms of CO2 emissions and form a complete list of baseline candidates.
Introduction
As one of the greatest challenges of our time, climate change has increasingly
become a top priority for governments, businesses, and general public.
According to the Environmental Protection Agency (EPA), the construction sector
has the third highest CO2 emissions among all industrial sectors. Construction
site activities alone contribute approximately 1.7% of total U.S. emissions, or
6% of national industrial carbon emissions (Truitt, 2009). Additionally, a
great amount of construction materials are being consumed every day, which
produce a magnitude of CO2 emissions due to embodied energy. For example,
approximately 110 million tons of cement is used every year in the construction
indsutry (Horvath, 2004). Embodied emissions from cement manufacturing and
processing represent 58.7% of the construction site emissions estimated by the
EPA (Hanle et al., 2004). Considering the fact that 54% of energy consumption
and 32% of CO2 emissions are directly or indirectly related to facility
construction and operation, the construction and facility management industry
will be one of the major sectors that should take more environmental
responsibilities and comply with stringent emission standards (Horvath,
2004).|
Commitments and efforts to reduce CO2 emissions must be based on accurate
emission inventory accounting and analysis. In the power and manufacturing
industries, Life-Cycle Assessment (LCA) methods have been developed to
establish the emission inventory baseline, including Economic Input- Output LCA
(EIO- LCA), and hybrid LCA (Seo and Hwang, 2001; WRI, 2005; ISO, 2006; Ochoa et
al., 2008; Sharrard et al., 2008; Yan et al., 2010). These models will need to
be adjusted and refined to suit for construction projects given the unique
nature and complexity of the construction sector (Truitt, 2009). Especially,
Construction managers today face a rapidly evolving and often bewildering array
of competing standards, approaches and regulations. They require practical
approaches to quantifying CO2 emissions, both for voluntary disclosure and
management as well as to meet emerging reporting requirements and regulations.
Existing studies on calculating CO2 emissions in construction projects,
however, cover disparate emission sources and produce distinct estaimates on
similar projects. This is well demonstrated by the emissions estimates ranging
from 300-1500 tons of CO2 emitted from constructing one lane-mile asphalt
pavement (Encord, 2010; Miller-hooks et al., 2010; Cass & Mukherjee, 2011).
It is urgent for the construction industry to establish a consensus on the
boundary, process, methodology, and reporting requirement to develop emission
inventory for construction projects and organizations.
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