Environmental Engineering Reference
In-Depth Information
involve questions of values, e.g., regarding how much risk to people or
to nature might be considered too much. Some climate changes could be
beneficial for some people or regions, while being damaging to others. For
example, with global warming, fewer people may die in cold waves while
more people die in heat waves; similarly, crops may be more productive
in parts of Canada while less productive in the United States, raising issues
of international food trade and transfer (see Section 5.1). Treatment of such
effects as cancelling one another would generally be a value judgment and
is not deemed to be appropriate here. Due to these considerations, we do
not comprehensively cover possible benefits of climate change that could
accrue to some people or regions. The study does not seek to evaluate the
financial costs or feasibility of achieving any given stabilization target, nor
to identify possible mitigation strategies to attain the targets.
The primary challenge for this study is to quantify insofar as possible
the expected outcomes of different stabilization targets using analyses and
information drawn from the scientific literature. Data available from pub-
licly available archives were used in analyses carried out for this study,
including, e.g., the CMIP3 climate model intercomparison project, the new
representative concentration pathway (RCP) scenarios, etc. Some analyses
and runs were also carried out, using published models and methods. The
report covers emissions, concentrations, changes in the physical climate
(such as temperature, rainfall, sea level, etc.) and their time scales, as well
as associated impacts (such as food production, flooding, ecosystem dam-
age, etc). In evaluating impacts, we seek to identify a baseline that includes
expectations regarding adaptation to climate change where appropriate, but
we also identify instances where adaptation is possible but where its feasibil-
ity, likelihood, or effectiveness is presently unknown. The report represents
a brief summary of a vast scientific literature and seeks to be illustrative and
representative rather than comprehensive.
Warming is the frame of reference for evaluation of impacts used in
this report for both conceptual and practical reasons. Many key future cli-
mate impacts are dependent upon the amount of global warming. Indeed,
available data and modeling suggest that the magnitudes of several key
impacts can be evaluated with relatively good accuracy for given amounts
of global warming. Much of the available literature and analysis of climate
impacts can be tied to specific warming levels but not readily linked to
CO
2
-equivalent concentrations (due for example to lack of specification of
aerosol forcing between studies). Indicated warming levels are related here
to the corresponding best estimates and uncertainties in CO
2
-equivalent
concentrations as well as to cumulative carbon emissions.
