Environmental Engineering Reference
In-Depth Information
1
Introduction
1.1 THE FOCI OF THIS REPORT: CLIMATE CHANGES AND
IMPLICATIONS FOR A RANGE OF ALTERNATIVE FUTURE WORLDS
The concentrations of several greenhouse gases (including carbon diox-
ide, methane, nitrous oxide, and other chemicals) have increased markedly
since the start of the 20th century due to human activities. The changes in
these gases very likely account for most of the globally averaged warm-
ing of the past 50 years (Hegerl et al., 2007). Carbon dioxide dominates
the anthropogenic radiative “forcing” of Earth's climate due to manmade
greenhouse gases. It has increased by more than 35% since 1750, now
reaching the highest levels in at least 800,000 years (Forster et al., 2007;
Luthi et al., 2008).
Human society faces important choices in the coming century regard-
ing future emissions and the resulting effects that should be anticipated
on Earth's climate, ecosystems, and people. One way of evaluating these
choices is to consider the climate changes and impacts that are projected
if human actions were to cause greenhouse gases to increase to particular
concentration levels and then stabilize. The focus of this study is on the
alternatives for the planet's future represented by stabilization of greenhouse
gases at a broad range of “target” levels, hereafter referred to as stabilization
targets. Transient climate changes and impacts experienced for increasing
concentrations of greenhouse gases are also considered.
This report does not recommend or justify any particular target. Rather,
our goal is to present the best scientific information available regarding the
implications of different targets for human and natural systems. The charge
to the committee was to evaluate the issue of serious or irreversible impacts
of climate changes.
It should be emphasized that choosing among different targets is a
policy issue rather than strictly a scientific one, because such choices
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