Are “planetary tipping points” likely? Trends in Ecology and Evolution recently published a very thought provoking article by Brooks et al. that challenges the notion of abrupt global threshold change. In the authors’ own words, we are likely to experience “[…] relatively ‘smooth changes at the global scale, without an expectation of marked tipping patterns.”

“Planetary tipping points” is not only a very important issue, with clear links to discussions about “planetary boundaries” and a “state shifts in the Earth’s biosphere”. It is also a very multifaceted inquiry that entails an electric combination between Earth system science, complex systems thinking, and science communication.

The paper opens up a whole set of important issues, but allow me to just briefly elaborate points that I find critical and interesting to explore and debate further.

1. Connectivity

Connectivity is a key factor in the assessment of the paper. As the authors note “If drivers or responses are spatially heterogeneous and inter-regional or intercontinental connectivity (through biotic or abiotic factors) is weak, the global aggregate pattern and rate of ecological change are likely to be relatively constant, without any identifiable tipping point. Conversely, if drivers and responses are spatially homogeneous or inter-regional or intercontinental connectivity is strong, ecological change might display a tipping-point pattern at a global scale.” (pp.2)

So, how strong is “intercontinental connectivity” between ecosystems? It depends on how you define “connectivity” of course. On the same page, the authors list a whole set of “biotic” and “abiotic factors” which underpin connectivity: species movement, ocean transport of heat, changes in CO2 levels, and others. Based on a brief analysis of these “connectors” for terrestrial ecosystems, the authors conclude that the “lack of strong continental interconnectivity, probably induce relatively smooth changes at the global scale, without an expectation of marked tipping patterns”.

Am I the only one getting the feeling that something is missing here? What I find intriguing in the analysis, is the absence of a discussion of “social connectors” which are likely to connect ecosystems across the world. The interconnected degradation of marine systems through global markets and new technologies denoted “roving bandits” are well known, and I see no reason why scholars should ignore similar phenomena for terrestrial ecosystems.

GWSP Digital Water Atlas (2008). Map 34: Virtual Water 2 (V1.0). Available online at http://atlas.gwsp.org

For example, while forest ecosystems in different continents might have few biotic and abiotic intercontinental connections, it is known that successful conservation policies in one region or a country, tends to shift environmental externalities to other areas through global markets (a “displacement effect” elaborated Lambin and Meyfroidt 2011). The flows of “virtual water”, and the observation that decreasing fish stocks force people to extract more resources from wildlife and tropical forests in West Africa (Brashares et al. 2004) are two additional examples of how social connectivity is tightly related to interconnected environmental change (some of which is likely to be non-linear). Global change scientists are just starting to get to grips with these complex human-environmental connectors (Adger et al. 2006, Young et al. 2006), but surely these would have an impact on how we analytically assess the sort of intercontinental connectivity Brook and colleagues are trying to get at? Bluntly put: if we indeed have entered the Anthropocene, why is social connectivity through institutions, technology and globalized trade, not part of the analysis?

2. Global tipping points and fatalism

The article ends with an interesting statement: “Second, framing global change in the dichotomous terms implied by the notion of a global tipping point could lead to complacency on the ‘safe’ side of the point and fatalism about catastrophic or irrevocable effects on the other.”

Brook also argues (in an associated blogpost) that “Why does this matter? Well, one concern we have is that an undue focus on planetary tipping points may distract from the vast ecological transformations that have already occurred.”

I find both these claims surprising. Surely a discussion about “thresholds” of this sort lead to more multifaceted social perceptions and responses than simple dichotomies of doom-and-gloom, or distraction? Nuttal and Hulme (which are quoted to support the first quote on framings) are just two articles in a much richer and multidisciplinary body of literature (raging from formal theory, to social-psychological experiments and case based approaches) that elaborates social perceptions, framings and responses to threshold phenomena. A somewhat more nuanced and empirically based discussion on this last issue of social perceptions and responses, could have contributed in significant ways to a much-needed discussion.