How close to the edge?

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In September, a diverse group of scientists—among them the Nobel laureate Paul Crutzen—presented in the journal Nature a new framework to analyze sustainable development at a global scale. This framework recognizes that humans have now become the main driver of global environmental change, and that our impact on the planet is growing stronger.

We are affecting every one of the major natural processes which are important for our own welfare, wrecking the ability of earth systems to regulate themselves, and buffer disturbances. In fact, our actions may be shifting earth processes to a completely new state that is a far cry from the extraordinarily stable conditions (in the entire history of planet earth) that allowed the development of human civilization since 10,000 BC. In the words of Paul Crutzen and colleagues, we have entered a new geologic era, the “Anthropocene”.

Our pressure on the planet appears more and more troubling as our understanding of earth processes improves. There is increasing evidence that many earth systems and biophysical phenomena do not change in a linear fashion, but rather experience abrupt changes when thresholds are crossed.

The Nature article, which summarizes a bigger report, is a first attempt to identify those earth processes affected by humans that are most likely to cause irreversible changes of a degree that may put development virtually out of reach, should the accumulated impacts push these processes beyond their thresholds. Nine global processes were chosen: climate change, the rate of biodiversity loss, interference with the nitrogen and phosphorus cycle, the depletion of stratospheric ozone, ocean acidification, global freshwater use, change in land use, atmospheric aerosol loading and chemical pollution.

The authors have quantified the current impact of humans on these processes and have proposed “safe” boundaries for each of them. By “safe”, they mean the maximum level of change that human activities can cause without these processes getting too close to a threshold that could transform them so significantly that there would likely be catastrophic consequences for the planet. In the opinion of the authors, safe boundaries have already been exceeded for three processes: climate change, the rate of biodiversity loss, and interference with the nitrogen cycle.

A first critical contribution of this approach is that it tackles questions that we can’t ignore anymore: How close are we to the edge? What is the edge? Or are we over the cliff already? How many cliffs and edges are out there?

A second important aspect of this framework is the focus on the connections between these nine processes. Our understanding of how processes are tied to one another is continuously advancing. Worsening conditions in one process can heighten the risk of crossing thresholds in other processes. For instance, further interference with the nitrogen cycle, and additional release of nitrogen oxides, can negatively affect the climate system.

The flip side is that good management in one area may have a positive effect on another. It is becoming increasingly obvious that many of these interactions are relevant in the context of climate change. Adaptation practices include elements of sustainable management of land and water, with potential positive effects on biodiversity and improvements for pollution reduction, while a number of co-benefits (or ancillary benefits) can originate from some mitigation options.

The Nature study on planet boundaries suggests that the current focus on holistic integrated approaches is even more critical than originally envisaged. We are still testing ideas in the field on how best to manage systems in an integrated way. These efforts need to be massively stepped up for development to stand a chance. It is undoubtedly difficult, but the urgency and magnitude of the challenges ahead call for immediate action.