Research pulling out the big-picture message from 4,600 different field experiments suggests that using ecosystem thresholds to develop environmental policies is unhelpful and could have dangerous consequences, it has been revealed.

The ‘tipping point’ concept suggests that ecosystems can absorb a given amount of environmental pressure before hitting a threshold. After they pass this tipping point, they can then change dramatically.

The concept plays a central role in many policies tackling global environmental change. For example, a policy may exist on the basis that if warming is kept below a certain threshold, ecosystems will continue to operate in a safe space.

But the international team of scientists behind the research, just published in leading international journal, Nature Ecology & Evolution, is now questioning this logic.

Safeguard ecosystems

Dr Ian Donohue, from Trinity’s School of Natural Sciences, said: “If thresholds are to be useful to assess and mitigate global environmental change we should be able to pinpoint them in existing environmental data or – better still – predict them for different drivers of environmental change so that we can safeguard ecosystems going forwards. From our analyses, this is not possible in virtually all cases.”

Professor Dr Helmut Hillebrand, biodiversity expert at the Institute of Chemistry and Biology of the Marine Environment (ICBM) at the University of Oldenburg, led the study.

He said: “In order to develop environmental policies we need a general guideline, but the problem is that, on one side, thresholds might be hard to detect in natural ecosystems when the anthropogenic change hasn’t been large enough yet. On the other side, we can’t determine thresholds for each process in each ecosystem.”

To understand how ecosystems respond to change the scientists turned to experimental data derived from already published synthesis efforts – so-called meta-analyses, which succinctly summarise the general outcome of many field experiments.

In particular, the analyses look at the consequences of present-day but also future pressures, such as increased CO₂ or nutrient levels. They also asses the functional responses of the ecosystems, such as changes in the cycling of elements or the production of biomass.

Information from 36 meta-analyses

In total the authors used information from 36 meta-analyses, which covered 4,601 unique field experiments on natural or close-to-natural ecological communities. This is the largest effort ever synthesising scientific literature on global change, according to the authors.

Whereas the vast majority of the 36 meta-analyses found that the strength of pressure affected the response magnitude – more pressure causes more damage – only very few (3 out of 36) showed statistical evidence for a threshold or tipping point – where a certain amount of pressure resulted in an extremely strong response.

Dr Ian Donohue added: “I think we need to abandon the idea of safe operating spaces. It gives the completely erroneous impressions that small pressures do not affect ecosystems at all, and that we can continue with business-as-usual so long as we keep our damage below a certain level. Instead, our research demonstrates that responses to even the smallest pressure can be large.

“If we wait to see clear tipping points in response to any of the major human-induced environmental changes such as warming or biodiversity change, we risk overlooking the small gradual changes which sum up to a shifting baseline over time, that is a shift in the perception of what a healthy ecosystem looks like.”

The scientists believe policy makers should readdress the use of thresholds in ecosystem management and instead work with more nuanced criteria to be able to act according to the precautionary principle. The underlying message: when the stakes are so high, we shouldn’t be gambling with our environment.