Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 27

present explanation for the fact that there was no significant drop in CO 2 concen-
tration over the past 22 million years while the climate cooled substantially.
Nevertheless, it is noteworthy that many paleoclimatologists are so convinced
from the start that CO 2 is the main driver of long-term climate change that, even
with noisy data, they claim support for their theory. Royer (2010) began his
commentary with the statement:

''Global temperatures have covaried with atmospheric carbon dioxide (CO 2 )
over the last 450 million years of Earth's history.''

It is noteworthy that prior to 2004, a number of climatologists pointed out
discrepancies between the geological records of climate and CO 2 over 500 million
years, whereas after 2004, most published papers emphasized the correlation of
climate and CO 2 over that period. It is not clear whether new data makes the
difference, or whether it is now necessary to support orthodoxy to obtain research
funding. Our conclusion here is that CO 2 is probably an important factor in long-
term climate change, but other factors are also influential such as the placement of
the continents on Earth, the functionality of ocean currents, worldwide distribu-
tion of clouds and aerosols, the past history of the climate, the orientation of the
Earth's orbit relative to the Sun, the luminosity of the Sun, the presence of aero-
sols in the atmosphere, volcanic action, land clearing, biological evolution, etc.
Hence, there is probably no single curve relating global average temperature to
CO 2 concentration, but rather, a set of curves that depend on the above factors.
From the limited accuracy of analyses of ancient climates conducted so far, we
still cannot pin down the expected D T G due to doubling CO 2 from 280 to 560 ppm
very precisely, but the rough indication from the LGM is that it may be in the
range 1 to 3 C. The merit of these estimates is highly questionable.

2.3.2 Introduction

One of the most pressing issues of our time is the possibility that rising CO 2
concentrations in the atmosphere might lead to significant global warming in the
future that could produce deleterious impacts on humankind. Hence, the relation-
ship between CO 2 concentration and climate has become a very central and
critical scientific issue. However, in addition to being a scientific issue, rising CO 2
has also become a political issue as well. This is due to several factors:

(1) In the process of consuming fossil fuels, cement production, and other industrial
activities, the world produces large amounts of CO 2 . If the world continues in a
business-as-usual scenario, CO 2 production will continue to rise in the 21st
century, leading to higher CO 2 concentrations in the atmosphere. The potential
cure for too much CO 2 requires a draconian change in the way that energy is
generated and used by the world, and this change may not be technically feasible
and, even if it turns out to be technically feasible, it will likely be extremely costly.
Indeed, it is possible that it may not be possible to provide the people of the world