Risk is often thought of as the product of consequences and likelihood—what can happen, and what are the odds of it happening. Both of these factors are important in determining whether and how we address specific risks. For example, even though the consequences of an asteroid colliding with the Earth would be catastrophic, the likelihood of it happening is extremely low in a time frame relevant to human society, and therefore, while we pay attention to the possibility, we generally focus on other concerns that may have fewer consequences, but have a much higher likelihood of occurring.
Projections of future climate change and climate impacts are inherently uncertain. To be clear, the question is not whether the climate will continue to warm, driven by greenhouse gas emissions from human activities. The overwhelming scientific consensus is that temperatures will continue to rise globally as a result of greenhouse gas emissions. Rather, the question is how much the climate will warm, how fast, and what the impacts will be. In very general terms, climate policy is about managing risk: assessing the potential impacts of climate change, judging how likely it is that various impacts will occur, and determining how our policy choices (discussed broadly here) will affect those risks. Uncertainty is a critical factor in assessing both climate risks and the effectiveness of different policy strategies.
There are two general sources of uncertainty in projecting future climate change: what we do and how the natural climate system responds. Uncertainty over what we do incorporates a broad range of social factors: possible trajectories for economic development, population growth, utilization of carbon-free energy sources, and other societal factors that affect greenhouse gas emissions. These sources of uncertainty become especially important beyond the next few decades.
The second component of uncertainty is the response of the climate system to increasing greenhouse gas concentrations—how much the climate will warm, how that warming will affect other processes like rainfall patterns and the natural uptake of carbon by the ocean and growing vegetation, how changes will be distributed across different regions, and so on. Even if we could predict exactly how emissions will play out in the future, we would still be faced with a range of possible climate change and a range for the severity of impacts.
These ranges, however, are dependent on the level of greenhouse gas emissions. Policy decisions can strongly influence the first source of uncertainty (future emissions), but will have little influence on the second source (climate response to emissions). We cannot know precisely what the severity of impacts will be for a specific trajectory for future emissions, but we can confidently say that the severity will be reduced if emissions are reduced. Policy makers must weigh the pitfalls of decision making under uncertainty. Extensively committing resources early may prove excessive, if climate change falls at the low end of the range. On the other hand, delaying or modestly committing resources may fail to prevent severe impacts, if climate change falls at the high end. A further complicating factor is that greenhouse gases emitted into the atmosphere can remain there for decades or even centuries, depending on the type of greenhouse gas. Therefore, simply waiting to see if impacts will be severe before making a decision will lock in even more severe impacts even if immediate action is taken at that point.
At an international level, a risk management approach is exemplified by the United Nations Framework Convention on Climate Change (UNFCCC), drafted in 1992 at the Earth Summit in
The authors of the UNFCCC only provided general guidelines for determining what “dangerous” means in this context. Article 2 states that, “Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.” But these are not the only criteria that can be used, nor do they suggest a single answer. Clearly, different people in different parts of the world, with different values and vulnerability will view different levels or types of climate impacts as “dangerous.” In future posts, we will explore the implications of the UNFCCC goal and how it relates to other climate policy efforts, as well as looking more closely at the implications of uncertainty for climate policy and methods for assessing climate risks.