There’s climate change, and then there’s climate change policy. In between the two is a heady mixture of jargon-laden physical, social, and economic science. If policy makers are to make real progress, we must start meaning the same thing when we use the same words. And we must illustrate complex concepts in a way that all of us breathing those heady vapors can live with and can use to communicate to policy makers. A changing climate manifests itself in many ways at various rates—some detrimental consequences occur slowly; others may occur abruptly. Many of the current and future effects of climate changes have been described in popular and scientific literature within the context of “tipping points,” which are usually thought of as triggering abrupt consequences. Kopp and colleagues survey the literature around tipping points and attempt to organize and probe the consequences in the context of integrated assessment models. Their new approach is one way to think about climate tipping points. As a way to further explore and for you to consider their proposed approach, AGU asked the authors of the article to highlight the important results that have emerged from their research and some of the important questions that remain.
What was the impetus of doing a review on ‘tipping points’ literature as it relates to climate science?
‘Climatic tipping points’ have been discussed, under that name, as a major climate risk factor for about a decade. Many specific climatic tipping elements—such as the Atlantic Meridional Overturning Circulation or marine-based ice sheets—have been identified as risk factors for at least a decade before that. Indeed, in some economic models dating back to the late 1990s, they are identified as the largest drivers of expected economic damages from climate change. Yet the actual literature on how such ‘tipping points’ translate into economic losses is quite sparse, and has yet to really benefit from a number of innovations within the field of climate economics that are advancing research into other ‘non-tipping’ climate damages. So we thought it was the right time to review the ‘climatic tipping point’ literature and identify prospective paths forward.
What were the main findings that emerged from your research review?
First, the ‘tipping point’ terminology is potentially confusing: its use in the climate science literature is clearly inspired by Malcolm Gladwell’s popularization, yet the use of the term in climate science doesn’t totally align with its popularized use. For example, Malcolm Gladwell characterized tipping points as ‘abrupt,’ but if we’re talking about ‘tipping points’ in an ice sheet, the consequences of crossing a critical threshold may take many centuries to play out. In our personal experience talking about these issues with the general public, we found that the ‘tipping point’ terminology made the consequences of crossing ‘climatic tipping points’ appear more imminent or abrupt than they might actually be. Second, for all our concerns about ‘tipping points’ in the climate system, we perhaps should be equally concerned about how ‘non-tipping’ parts of the climate system might cause social tipping points—for example, involving civil conflict or migration—or shocks to the economy.
So one goal of this paper is to offer a set of terminology that doesn’t conflict with popular understandings and can be consistently applied across both natural and human systems. For example, we prefer the term ‘critical threshold’ to ‘tipping point,’ because it doesn’t carry the connotation of ‘abruptness’ that ‘tipping point’ does. Another goal is to encourage researchers to look at climatic tipping elements, social tipping elements, and climate-economic shocks in a coherent framework, rather than focusing just on climatic tipping elements.
The ‘lag’ (or lack thereof) you discuss is important; can you explain how this lag affects our ability to address climate related crises (what you term ‘climate-economic shocks’)?
The non-abruptness—the lag—in how critical thresholds in many climatic tipping elements play out is of importance for a couple reasons. First of all, a ‘tip’ that takes many centuries to play out may not matter much for conventional economic analyses; the consequences may be too far in the future, or happen slowly enough that we can readily adapt to them. Second, if a ‘tip’ plays out either too quickly or too slowly, we may not be able to detect when it has occurred until it is too late to do anything about it, whereas with a moderate amount of lag, we may be able to change course on emissions or intervene through some form of geoengineering before we are fully committed to its consequences.
What are the implications of the issues you address for climate scientists? And where are additional modelling or data efforts needed?
Our review has a few implications for research directions. First, there are a lot of exciting innovations happening with regard to the modeling of climate change impacts and economic damages generally; we think these innovations can be combined with improved modeling of the natural system components of some climatic tipping elements to really understand which tipping elements we, as humans, should be focused on better understanding. Second, social tipping points—whether involving positive changes (such as those that advance mitigation or adaptation), negative changes (such as those that involve conflict), or ambiguous changes (such as those involving migration)—may be just as if not more important to us humans than critical thresholds in climatic tipping elements. Yet this area has received much less research attention. Third, we think that more work could be done identifying the triggers that we know cause significant economic shocks—things like large-scale environmental disasters and civil conflicts with clear environmental connections, but also things like financial crises with less clear connections—and investigating how these might be affect by climatic change.
What about the implications for society?
For society at large, it’s clear that there are a lot of potential surprises out there associated with climate change—‘unknown unknowns’ as Donald Rumsfeld might have called them. Many of these may involve rapid, non-linear changes in either the physical climate or human systems. So we need to get a better handle on these changes and their associated risks for humans. Yet it’s hard to do, and much of the research on climate damages is currently focused on easier-to-characterize changes, such as those involving the crop yield or mortality effects of changes in mean temperature and precipitation. Those are important, but they’re not the full picture, and we can’t neglect these harder questions.
—Michael Ellis, Editor, Earth’s Future; email: mich[email protected]