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A recent article, Montoya et al., in the journal Trends in Ecology and Evolution is based on a fundamental misrepresentation of the Planetary Boundaries framework.
Their representation of the framework is directly contradicted in all of the papers presenting the planetary boundaries framework (Rockström et al, 2009a; 2009b; Steffen et al., 2015). What’s more, Montoya et al. repeat earlier misrepresentations of the research. Thus, it would appear that Montoya et al. derived their understanding of the planetary boundaries framework from secondary, rather than primary, sources.
We are surprised that the discrepancy between the Montoya et al. representation of the planetary boundaries and that presented in the primary literature was not picked up in peer review.
We note as well that the tone of the Montoya et al. contribution is unusually normative and personal, thus undermining its potential value as a constructive contribution to an important scientific debate. The paper presents a vitriolic and opinionated critique on the Planetary Boundaries framework and in particular the biodiversity (biosphere integrity) boundary. All of this is unfortunate as Montoya et al. make many valid points with which we are in agreement in their discussion of biodiversity challenges at the local and regional level.
Briefly, Montoya et al. conflate tipping points with planetary boundaries with such claims as:
"How best should environmental science articulate its concerns, set research agendas, and advise policies? One solution embraces the notion of planetary boundaries  arguing that global environmental processes very generally have ‘tipping points’. These are catastrophes involving thresholds beyond which there will be rapid transitions to new states that are very much less favorable to human existence than current states."
"The rate of human-caused extinction…is one of two of the nine global processes deemed to have exceeded a purported tipping point."
These statements are blatantly incorrect. Any author or reviewer who has read the primary Planetary boundaries literature would know this to be the case. Steffen et al. (2015), for example, clearly state:
"A planetary boundary as originally defined is not equivalent to a global threshold or tipping point."
To build their case, Montoya et al. neglect this clear and unambiguous statement, which forms the basis of the theoretical framework and thus runs systematically right through the entire analysis of defining and quantifying planetary boundaries.
We find it surprising that the Montoya et al. Forum piece includes the same misrepresentation as the Breakthrough Institute’s error-filled 2012 article (published to coincide with the UN Rio+20 conference) (Blomqvist et al., Breakthrough Institute 2012), to which we replied by explaining, just as now, the fundamental misrepresentation of the framework.
We also find it surprising that the referees did not pick up on Montoya et al.’s reliance on highly selective statements from a talk given by Rockström at the World Economic Forum in 2017 in support of their critique. This talk is both an extremely unusual reference in the peer-reviewed literature and completely irrelevant to the arguments made in the Montoya et al. paper. The statements made in the talk had (1) nothing to do with the Planetary Boundaries framework, and (2) say nothing about biodiversity-related tipping points.
In the following we offer a brief correction of the misrepresentations in Montoya et al., and close by making clear that their speculation on the policy implications of adopting a planetary boundaries framework is nothing more than their own personal opinions.
In support of this statement we will also publish a full response in TREE.
20 November 2017,
The environmental processes selected for inclusion in the planetary boundaries framework are those that are known to contribute to regulating the Earth System, i.e. operate at a planetary level. Some of these processes (for example climate through ice melt) are known to exhibit threshold or “tipping point” behavior. However, most – including biodiversity/biosphere integrity – are assumed not to (see Figure 4, Rockström et al 2009b and Steffen et al, 2015). Even in the few cases where the scientific evidence supports threshold behavior, the identified planetary boundaries are not placed at the estimated point (for a control variable) of a threshold.
The existence (or otherwise) of thresholds and/or “tipping point” behaviour in the processes included is thus not a pre-assumption or requirement to the planetary boundaries framework.
Montoya et al’s critique is founded on a deep misunderstanding of the Planetary Boundaries framework. In the Planetary Boundaries research, we have never claimed that there is a planetary scale biodiversity tipping point. Furthermore, the Planetary Boundary framework does not state that any global processes have exceeded tipping points (See Steffen et al., 2015).
We include biodiversity (in the latest scientific update, Steffen et al., 2015, defined as biosphere integrity to emphasise the functional and regulatory role of biodiversity for ecosystem stability) as a planetary boundary on the scientific ground that the biosphere interacts with the climate system, hydrological cycle and other biogeochemical cycles in the Earth system, and thereby contributes to the regulation of the state of the Earth system.
Furthermore, for most of the long history of the Earth system, the geosphere and biosphere have co-evolved as a single, interacting system, emphasising the very important role that the biosphere plays in the stability of the Earth system as a whole (Lenton 2015).
Based on this evidence, therefore, the inclusion of biodiversity as a planetary boundary is justified by the aggregate and interacting role of biomes in regulating the stability of the Earth system, a role that at smaller scales is evidenced by the role it plays in ecosystem stability. This, as stated by Montoya et al., is their focus as well. So, in essence, we are in agreement - biodiversity contributes to the regulation of the stability of ecosystems and consequently aggregates across scales to the Earth system as a whole.
The Planetary Boundaries framework thus provides a complement to the myriad methods and approaches for ecosystem management [not least as advocated by Montoya et al.], by attempting to provide an Earth system-level framing. As specifically pointed out in Steffen et al., 2015, the planetary boundaries approach is not intended as a replacement for ecosystem management approaches but a complement that takes Earth system considerations into consideration.
The Planetary Boundaries framework has never been proposed as a panacea to replace all the necessary and important approaches, from conservation policies, payment schemes for ecosystem services to marine protected areas and Aichi targets.
The Planetary Boundaries framework evolved from the major advancements in Earth system science over four decades, ranging from evidence and insights on the Anthropocene (Steffen et al. 2016), tipping elements in the Earth system (Lenton et al. 2008), ecological resilience (Folke et al. 2004), multiple stable states in biomes (Scheffer 2009) and the biosphere-geosphere regulatory interactions noted above (Lenton 2015).
The first publication of the Planetary Boundaries framework in 2009 was followed by a deep peer-reviewed scrutiny, e.g., those by Carpenter and Bennett (2011) and deVries et al. (2013) on the biogeochemical flows boundary.
We welcome this scientific critique, which has improved the Planetary Boundaries definitions and the assessment of quantitative boundary levels for control variables.
There is rising scientific evidence that planetary stewardship is required to enable a sustainable future for humanity on Earth in the Anthropocene (e.g., Folke et al. 2016). While action, methods, policies, investments and management occur locally and across scales, in the Anthropocene, due to the planetary scale of human pressures on the Earth system, this all must add up at the Earth system level. Just as all countries need to decarbonise energy systems by 2050-2060 to "add-up" within a climate planetary boundary of 1.5 degrees Celsius, there is evidence that biomes, from rainforests to coral reefs to tundra/permafrost, need to remain stable to enable world development on a planet that remains reasonably stable in something resembling an interglacial state.
The Planetary Boundaries framework offers, for the first time, an attempt to identify all the critical, interacting processes on Earth that contribute to the stability and resilience of the Earth system as a whole. This draws on the best knowledge we have today on the quantitative boundaries within which we are likely to remain in (or return to) a Holocene-like state, but beyond which we are at increasing risk of eliminating that possibility.
As such, the Planetary Boundaries framework offers an attempt to define biophysical science-based targets at the Earth system level as a response to humanity now being in the Anthropocene. As emphasized in the Steffen et al (2015) paper, the Planetary Boundaries framework should be seen as a complement – and not a competitor – to ecosystem and other sustainability management principles and methods developed, and effectively adapted, for different scales and sectors.
Today, Planetary Boundaries provide scientific support for an integrated Earth system approach to global sustainability, integrating, e.g., biosphere sustainability with climate mitigation. It provides a framework for defining science-based global targets that go beyond "CO2 only", to include biodiversity, nitrogen, phosphorus, water, and land, i.e., biosphere functioning.
It is, in short, an Earth system-level framework that builds upon and supports sustainable development and ecosystem management across scales. It does not replace them.
Montoya et al. question whether there are any thresholds associated with biodiversity in ecosystems altogether with their statement “neither theory nor empirical data support any threshold of biodiversity below which ecosystem function is compromised”.
This contradicts the scientific evidence. Again, if the authors had followed the literature and the advancements in planetary boundaries research, they would have followed the exchange in 2012, where Brook et al. 2013 questioned whether there is a planetary scale tipping point in the terrestrial biosphere (i.e., exactly the same misinterpretation as Montoya et al. in 2017).
Moreover, this misrepresentation was also published in TREE.
Hughes et al., (2013) answered this misguided critique by (1) making it clear that the Planetary Boundaries framework has never claimed to postulate a planetary-level biosphere tipping point; (2) presenting clearly the scientific evidence that there are multiple stable states in ecosystems, i.e., biodiversity-coupled tipping points in ecosystems (which Montoya et al. claim do not exist); and (3) summarizing some of the emerging scientific literature suggesting that there may, after all, be a planetary scale biodiversity tipping point (as suggested by Barnosky et al. 2012).
So, fundamentally, Montoya et al., trod down old ground, subsequently discussed in much more detail in the scientific literature. It is a disappointment that the same misrepresentations and unfounded aggressive critique resurface five years later and in the same journal.
This discussion notwithstanding, whether or not biodiversity/ecosystems exhibit threshold responses is immaterial to the Planetary Boundaries framework. Indeed, Steffen et al. (2015) explicitly state that change in biosphere integrity is one of planetary boundary processes assumed not to have a singular threshold at the global or continental/ocean-basin level.
Anyone who has carefully studied the planetary boundary literature can, therefore, be in no doubt that there is absolutely no expectation of a “tipping point” or a “threshold” with respect to biodiversity/biosphere integrity implicit in the framework.
Montoya et al. make an unsubstantiated claim that the planetary boundaries framework potentially leads to perverse policy. Incredulously, they seem to be of the opinion that adopting Planetary Boundaries lowers ambitions towards global sustainability, and once the world succeeds in transitioning into the biophysical "safe operating space" within planetary boundaries, the world would lean back and return to unsustainable business-as-usual practices:
"…the planetary boundary framework suggests that we can view nature and its complex ecological processes as a type of blackbox – if we do not poke it too hard, we will not need to understand its details. We need not define measures, terms, processes, responses in operational ways. In short, ecological ignorance is bliss, if human actions remain within limits."
This is an astonishing and clearly a personal opinion held by the authors. The biodiversity (biosphere integrity) boundary is positioned at <10 extinctions/million species per year. We are today at a rate of extinctions 10 - 100 times higher. Returning to a safe operating space for biodiversity will require a major transformation in ecosystem management across all land-based and marine ecosystems across the world.
Once the world returns into a safe operating space for biodiversity [let’s assume we succeed!], is it likely [or even possible] that the Planetary Boundaries framework will encourage some form of "ecological ignorance" and unsustainable use of ecosystems? Of course not.
Transforming societies back to within the safe operating space of planetary boundaries, for all boundaries, requires adoption of sustainable practices that - once on safe ground - obviously need to be sustained to remain sustainable. Take, for example, the stratospheric ozone boundary, where the world transgressed the boundary in the late 1980s but has returned back to within the safe operating space through global concerted implementation of the Montreal Protocol, phasing out ozone depleting substances, and has remained anchored in this new social state.
And, honestly, if Montoya et al. were right, why would this bizarre assumption (that sustainable management is suddenly abandoned once sustainable targets are met) not apply to the CBD and the Aichi targets which Montoya et al. applaud as a much more concrete and adequate way forward toward ecosystem management?
Meeting the Aichi targets is, evidently, a much less ambitious task than meeting the planetary boundary on biodiversity. It is though, interestingly (given that Montoya et al. applaud it so strongly as concrete while critiquing the Planetary Boundaries as vague and dangerous for policy), set almost exactly in the same way as the planetary boundary.
Setting aside 17% of land area and 10% of the ocean as protected areas are global quantitative targets very similar to the combined land and biodiversity boundaries of safeguarding a minimum of 75% of critical forest biomes and reducing extinction rates to below 10 extinctions/million species per year. The implication of these Planetary Boundaries is essentially that we need to ensure zero or close to zero future expansion of agricultural land, i.e., ensure that 50 % of land area remains as natural ecosystems [given that we have already transformed ~40-50 % to agricultural land], which is several magnitudes more challenging than meeting the Aichi targets [setting aside 17 % of land-based ecosystems].
So, in the Montoya et al. projection of the future, we would meet the Aichi targets well before the planetary boundary on biodiversity. But what happens once we meet the Aichi targets?
If the world, according to Montoya et al., leans back and does nothing once the planetary boundary is met, what hinders the world to do the same once the Aichi targets are met, moreover, much earlier? Of course, this is not going to happen. If the Aichi targets are met, continued conservation of ecosystems is needed to remain on the "right side" of Aichi.
The same applies to the planetary boundaries.
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