DO GLOBAL WARMING AND CLIMATE CHANGE
REPRESENT A SERIOUS THREAT TO OUR WELFARE
AND ENVIRONMENT?
By Michael E. Mann
I. Introduction
The subjects of "global warming" and "climate change" have become
parts of both the popular lexicon and the public discourse. Discussions of
global warming often evoke passionate responses and fierce debate between
adherents to different views of the threat posed. Yet there are many nuances
regarding global warming, climate change, and the threats they represent
that are not well understood by the public. The public's conceptual under-
standing hinges largely on images and paradigms within the popular
culture that are often little more than caricatures of the actual, underlying
scientific concepts. To appreciate the potential threat that climate change
and global warming represent to human society, living things, and our
environment, it is necessary that we first understand the true science
underlying these phenomena.
The purpose of this essay is to assess the implications of climate change
for the welfare of human society and our environment.
I will first discuss
the science underlying global warming, climate change, and the connec-
tions between these two phenomena (Section II). I will then explore what
climate changes are projected for the future under various plausible sce-
narios of future human behavior (Section III), and what impacts these
changes are likely to have on society, ecosystems, and our environment
(Section IV). Finally, I will consider the economic, security, and ethical
considerations relevant to evaluating the threat of climate change (Sec-
tion V) and the steps that should arguably be taken to mitigate climate
change and its impacts (Section VI). I will summarize my conclusions
Section VII.
II. Scientific Background
Global warming
refers to the phenomenon of increasing average surface
temperatures of the Earth over the past one to two centuries. The concept
is related to the more general phenomenon of
climate change,
which refers
to changes in the totality of attributes that define climate
-
not only sur-
face temperatures, but also precipitation patterns, winds, ocean currents,
and other measures of the Earth's climate. For this reason, I will favor the
doi:10.1017/S0265052509090220
é 2009 Social Philosophy & Policy Foundation. Printed in the USA.
193
'
climate change
'
throughout this essay,
recognizing that global warming is simply one of the attributes of climate
change. Climate change can be viewed as consisting of two components,
one of which is human (i.e., anthropogenic) in origin and coincides in
timing with the industrial period of the past two centuries, and the other
of which is natural and has played a role in both past and current climate
variability. Global warming generally refers to the anthropogenic com-
ponent of climate change alone, and only the surface warming associated
with it. The key scientific issues required to understand the behavior of
the Earth
'
s climate system are discussed below, and include the notion of
energy balance,
which governs how the climate system works, the
green-
house effect
(including the special case of the
enhanced
or
human
green-
house effect), which is necessary to understanding surface temperatures
on Earth, and so-called
feedbacks,
which can amplify the magnitude of
climate changes. Other essential aspects of the science of climate change
are the construction and use of theoretical
climate models
to investigate the
behavior of the climate system, an understanding of the factors that have
governed past climate, and, finally, the inferences that can be drawn
through a comparison of model simulation predictions and available obser-
vations in the assessment of the human impact on climate.