ASHRAE Journal - May 2023 - 14

LETTERS
was the key point of your lead-in
sentence. A commonly accepted
definition of a pollutant (in our
paraphrase) is the emission of a
substance that will have a negative
impact on some aspect of the natural
environment.
For CO2 there are some potential
positive factors, that you point out,
but there are also negative factors,
which you do not. Indeed, as you
mention, increased CO2 levels up to
a point increase the photosynthetic
potential of plants, which has been
recognized as a possible benefit.
For a well-sealed agricultural
greenhouse, the consumption of
CO2 by plants can decrease the CO2
levels of the air inside that greenhouse
to the 150 ppm to 200 ppm
level (compared to the current
concentration in the air outside a
greenhouse that is in the range of
the low 400s ppm). Greenhouse
operators may therefore choose
to add CO2 to their air to help the
plants continue growing. Hence,
one may confuse what is an acceptable
level of CO2 in the range of 100
ppm or 200 ppm, as you mention in
your response.
However, that does not recognize
the reality that the actual ambient
concentration in the earth's atmosphere
now exceeds 400 ppm. In
preindustrial times (before 1800),
the CO2 concentration was roughly
280 ppm, and based on the real-science
ice core samples that we have
it has not exceeded 300 ppm in the
past 400,000 years. Thus, scientific
evidence has clearly documented
that volcanic activity or other natural
phenomena other than human
activity did not increase the CO2
concentration to anywhere near the
current levels.
14
Furthermore, solar activity is not
a driving factor to consider since
the amount of solar energy incident
on the earth has actually slightly
declined in the past few decades
(see " Is the Sun Causing Global
Warming? " from NASA: https://
tinyurl.com/2p97y9e4). There is
also clear scientific evidence that
global ambient CO2 levels of the
800 ppm to 1,400 ppm range have
not been that high for at least 20
million years, while there is a
strong scientific belief that these
would be actually catastrophic for
the environment and humankind.
The global environment is changing,
and increasing temperatures
are recorded throughout the world,
with records from worldwide
sources documenting global warming.
Although CO2 is not the only
factor, it is recognized by world
leading scientists who do this work
and international organizations
like IPCC of the United Nations as it
being a significant factor.
The last half of your letter deals
with many issues outside the topic
of our article-for example, the
thinking that ASHRAE " followed
bureaucrats " when deciding on
outdoor airflow rates for buildings.
The reduction in outdoor air set by
ASHRAE Standard 62.1 in response
to energy concerns of the 1970s was,
admittedly in hindsight, a mistake
but this has been corrected and
lessons learned in terms of taking
the necessary precautions in the
efforts to handle energy savings
while securing the proper indoor
environment.
On one of your other points, it
is true that heat pumps' performance
drops near freezing, but
already heat pump technology is
ASHRAE JOURNAL ashrae.o rg M AY 2023
making good progress even in cold
climates. In any event, there are
different considerations and optimal
solutions for different buildings
in different climate zones. The
issues related to how fast we should
proceed with the electrification of
buildings, transportation and the
electrical grid by exploiting different
solutions and technologies are
key issues of the overall decarbonization
discussion.
More energy efficient buildings
can be designed, constructed and
operated to have a much lower
energy demand and rely less on carbon
emitting energy sources. At the
same time the electrical grid must
be adapted to lower carbon emissions,
but that is an issue beyond
the topic of this article. All of these
will take time but we also as a society
need to move in the right direction.
Thomas Lawrence, Ph.D., Fellow ASHRAE,
Athens, Ga.; Costas Balaras, Ph.D., Fellow
ASHRAE, Vrilissia, Greece
What About Water
Vapor as a GHG?
I read, with interest, the article by
Dr. Lawrence and Dr. Balaras. I am
100% supportive of the role ASHRAE
is developing to decarbonize buildings
and appreciate the leadership
both authors are exhibiting.
My only problem is this sentence:
" Carbon dioxide has long been
recognized as the most significant
GHG... " This is categorically untrue.
In fact, water vapor is the most
significant and greatest quantity
GHG. Even NASA has recognized
that moisture and clouds could
create significant impacts, both
radiative and infrared feedback.
They commenced a study of such
https://tinyurl.com/2p97y9e4 https://tinyurl.com/2p97y9e4 http://www.ashrae.org
ASHRAE Journal - May 2023

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