values in current projections. For example, a climate change-induced crop failure or severe drought could precipitate a geopolitical crisis.18 There may also be “tipping points” in the climate system or affected human or natural systems, whereby a small incremental change pushes the system into a sudden and radical shift.19 Currently, it is impossible to predict where or when such crises, tipping points, or other surprises might occur. It is worth noting, however, that the potential impacts associated with larger magnitudes of climate change are less well studied than more moderate climate change; and thus the potential for surprises is comparatively greater with larger magnitudes of warming.


The many complex characteristics of climate change discussed here—which reach across scientific, political, economic, psychological, and other dimensions—are not problems that must be fully “solved” before one can move ahead with making choices and taking action to address climate change (see Box 3.2). Rather, these are inherent features of climate change that must be recognized and understood in order to craft sound response strategies. As discussed later in this report, many possible response actions could be viewed as common-sense investments in our nation’s future regardless of the complexities and uncertainties involved.

The issues highlighted in this chapter point to the idea that conventional analysis tools that have historically been used for guiding responses to major environmental problems are not well suited for addressing the complexities of climate change.20 Instead, there is a need for decision frameworks that allow decision makers to weigh trade-offs, to act in the face of incomplete information, and to learn and adjust course over time. In the following chapter, we discuss the type of framework that is best suited for this context.

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