Page 41 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

24 Cha pte r O n e

chapters. The USGBC has made a commitment to focus on emphasizing strategies and
green building goals which would help lower the emission of carbon dioxide into the
atmosphere. Carbon dioxide is recognized as a gas with a global warming potential
(GWP) and is thought to be a major contributor to current changes in the atmosphere.
Carbon dioxide levels in the atmosphere have increased in recent decades, as has the
use of fossil fuels for energy. Fossil fuels are carbon based, and their use is thought to
impact the global carbon cycle, with more carbon being released to the atmosphere (in
the form of carbon dioxide) than sequestered in the crust, ocean, or flora (usually in
dissolved, fossil fuel, mineral rock, or vegetation form). Fuels that cannot be readily
reproduced in our human-generation time frames, such as fossil fuels, are referred to as
nonrenewable, whereas energy sources such as wind or wood which can be regrown are
referred to as renewable. Even though the burning of wood releases carbon into the air
in the form of carbon dioxide, it is considered renewable with respect to the carbon
cycle, since new trees recycle carbon from the atmosphere during their growth.
Renewable energy sources that are still a part of the carbon cycle such as corn-based
ethanol or wood-burning are typically referred to as carbon-neutral. Other energy sources
such as wind harvesting which do not use carbon-based chemicals as part of the energy
transfer mechanism are referred to by the author as carbon-free.
In late 2006, the USGBC announced some very progressive goals for reducing
carbon emissions. These have resulted in an increased emphasis on energy efficiency
and the use of renewable energy in LEED 2009. This is evident in the additional points
which are awarded in LEED 2009 for many credits which improve energy efficiency or
decrease dependence on fossil fuels. Optimizing energy performance as a part of the
carbon commitment will reduce energy use, and as most energy use in the United States
is based on fossil fuels, this should result in decreased dependence on fossil fuels and
decreased carbon emissions from these nonrenewable fuels.

References
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