ASHRAE Journal - February 2023 - 30

FEATURE
Recognition of GHG Emissions as a Pollutant
Carbon dioxide has long been recognized as
the most significant GHG that traps heat in the
atmosphere by absorbing the long wavelength
infrared radiation from the earth back out to space,
thus preventing that natural cooling effect. At the
time when this was first recognized in the mid1800s,
average ambient CO2 concentrations were
around 290 parts per million (ppm); currently, these
concentration levels are nearly 420 ppm. Recognition
of the resulting warming effect and climate
impacts of rising CO2 levels has incentivized
the building decarbonization movement,
which is working to achieve reduction
in GHG emissions associated with the
construction and operation of buildings.
Over time, a solid consensus has emerged
in the scientific community that climate
change toward a warmer Earth is occurring,
and that human activity is the primary driver,
though acceptance of this science has been
irregular, depending on the country and existing
political and economic predispositions of politicians
and citizens. This has motivated the development of
numerous global agreements and actions. The most
recent legally binding international treaty on climate
change is the Paris Agreement4 that sets out a global
framework to avoid dangerous climate change by
limiting global warming to well below 2°C (3.6°F) and
pursuing efforts to further limit it to 1.5°C (2.7°F).
In the U.S., there has been a two steps forward, one
step back approach in addressing CO2 emissions.
In 2007, the U.S. Supreme Court ruled that the
Environmental Protection Agency (EPA) should
consider CO2 and other GHG as pollutants within
the context of the Clean Air Act, which allowed for
regulatory changes in increasing fuel efficiency
for vehicles and electricity generation. In 2015,
President Barack Obama first proposed the Clean
Power Program, designed to reduce CO2 emissions
by requiring existing fossil fuel electric generation
facilities to operate more efficiently and to encourage
the adoption of more zero- or low-carbon emission
energy sources. This program was nullified by the
Trump Administration in 2017, and later challenges
in the judicial process led to the recent U.S. Supreme
Court ruling in July 2022 that the EPA overstepped its
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F E B R U A RY 2023
authority regarding regulating emissions from electric
power plants, thus leading to a regulatory stalemate.
The U.S. Congress addressed this in the Inflation
Reduction Act, which was passed in August 2022. This
act amended the Clean Air Act to explicitly define CO2
as a " pollutant " as treated by this Act. These legislative
developments, though, have not changed the trend in
the industry to " decarbonize " the built environment.
The European Union (EU) has, over the decades,
adopted several energy strategies leading to various
energy and environmental policies, legislations and
other initiatives setting ambitious short- and nearterm
targets.5 In particular, the EU has committed
to support the United Nations' efforts to address the
climate crisis and aims to have Europe be the first
continent to reach a decarbonized economy by 2050.6
To support these efforts, energy efficiency remains the
priority for reducing energy consumption, along with
increased use of renewable energy sources in order
to reduce GHG emissions and dependency on fossil
fuels. In particular, energy-related GHG emissions
from building operations account for ~23% of total EU
emissions. As a result, the buildings sector is center
stage of current European policies to decarbonize the
economy in line with the Paris Agreement.
Decarbonizing Buildings
First, we must ask what it means to decarbonize a
building? Looking at the bigger picture, a building's
carbon (and GHG) footprint includes all emissions
associated with a building from " cradle to grave. " The
combined GHG emissions include not just CO2, but
various other gases such as methane, nitrous oxide and
hydrofluorocarbons that contribute to global warming.
When measuring their impact on the climate, non-CO2
emissions are converted into CO2 equivalents (CO2e)
based on the individual component's global warming
potential (GWP), usually based on the impact expected
for a 100-year integration timeline. (See for example
Table 4 in Chapter 36 of the 2021 ASHRAE Handbook-
Fundamentals for the GWP based on the 100-year
timeline for refrigerants.) Activities that result in CO2e
emissions include the building construction, operation
and, finally, the demolition/repurposing phases.
Decarbonization does not mean (at least for now) a
complete zero-carbon emission rate, but rather the
trend toward significantly reducing the emissions of
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ASHRAE Journal - February 2023

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