What PBs Tell Us

Which PBs have we transgressed, and how do we know?

Firstly, it is important to note that in addition to quantitative methods, early-warning signs can indicate approach towards a threshold.

Statistically, the proposed PBs are placed significantly before reaching the threshold; the buffer in between accounts for uncertainty and the element of Surprise.

(Source: Science, 2015)

Of the PBs presently quantified, individual safe operating space and present positions are quantified to the following levels:

Climate Change
Based on IPCC reports in 2012 and 2013, the safe operating space is below an atmospheric CO2 concentration of 350ppm and an increase in top-of-atmosphere radiative forcing of +1.0Wm^–2 relative to 1750. Human-driven changes to radiative forcing include CO2, other greenhouse gases, aerosols, and other factors that affect the energy balance. Present values are 406.75ppm CO2 and +2.3Wm^–2. Hence, the boundary has been transgressed. Early-warning signs that indicate transgression are the increase in heat waves, the increase in heavy rainfall events, increased drought, and mass loss of ice sheets. The problem of system inertia needs to be taken into account in assessing the time needed for society to react to early-warning signs.

Ocean Acificiation
The boundary is defined as ≥80% of the preindustrial annual average global Ωarag. Present global value is 84%, within safe boundaries. It would not be transgressed if the Climate Change PB were respected, and system inertia means future risk will increase.

Stratospheric Ozone Depletion
Boundary of minimum ozone concentration is defined as 275DU. Concentration drops to 200 DU only over the Antarctica in the austral spring, transgressing the boundary regionally. This is the ozone hole. Global concentration has been steady for 15 years and is expected to rise as the ozone hole is repaired after environmental policy phased out ozone-depleting chemicals.

Ozone-Depleting Chemicals (Source: Ozone Assessment 2010)

For PBs with sub-planetary scale dynamics, units of analysis vary. Changes in Biosphere Integrity occur at the level of land-based biomes, large freshwater ecosystems, or major marine ecosystems. Land-System Change in biophysical climate regulation is primarily related to changes in forest biomes. Freshwater Use occurs in the major river basins around the world. Biogeochemical Flows aggregate from localized but severe perturbations in intensive agricultural zones to affect global flows of nutrients.

(Source: Science, 2015) 

I shall focus on those transgressed.

Biogeochemical Flows 
The global-scale boundary for Phosphorus is set at a sustained flow of 11TgP/year from freshwater systems into the ocean. At a sub-planetary scale it is 6.2TgP/year from fertilizers to soils. The present global rate of application of Phosphorus to croplands is 14.2TgP/year, well above the PB. For Nitrogen, the PB for eutrophication of aquatic ecosystems is 62TgN/year, which we have significantly transgressed, at 150TgN/year. From the above diagram, the main contributors to these transgressions are a few agricultural regions of very high P/N application rates.

Land-System Change
The major forest biomes play a stronger role in land surface–climate coupling than other biomes. The biome-level boundary for tropical and boreal forests are set at 85% of potential forest, and that for temperate forests at 50%. The diagram above summarises risk of sub-planetary scale transgressions. The global boundary is set at 75% of original forest cover, which is transgressed: present forest cover is 62%. It would not be transgressed if the Biosphere Integrity PB were respected.

Biosphere Integrity
The Biodiversity Intactness Index (BII) assesses anthropogenically-caused change in population abundance across a wide range of taxa and functional groups at a biome or ecosystem level using preindustrial abundance as a reference point. Though the PB is set at 90%, the high degree of uncertainty, 30-90%, makes the present value, 84%, appear much less significant a transgression than represented on the wedge.

Atmosphere aerosol loading
The annual mean Aerosol Optical Depth (AOD) is presently at 0.3. The proposed boundary proposed is 0.25 (0.25-0.50), indicating transgression within the zone of uncertainty. A substantial decrease in monsoon activity can be used as an early-warning sign, and would occur at AOD 0.50.

(Source: Science, 2015)

From the supplementary materials, we find many additional proposals of methods and values for boundaries and present positions. The summary diagram in each paper, such as the one above, give us a general idea. One would have to complete many PhDs to understand the specific quantification methods behind each PB!

Which PBs should be policy priority?

The extent of transgressions informs policymakers of the urgency of each environmental problem. However, the paper has made it clear that there is a high degree of uncertainty in the quantification of each boundary and each transgression risk. Although control variable wedges have been normalized for the zones of uncertainty, the exercise of representing all PBs with vastly differing measurement units on one chart is like comparing apples with oranges.

The hierarchical approach to classifying the boundaries suggests that two of the PBs, climate change and biosphere integrity, are recognized as “core” PBs based on their fundamental importance for the Earth System and integration with the other PBs.

The scale of tipping points determines importance of PBs to organisations of different scales. International organisations should prioritise planetary-scale tipping points, while smaller organisations may find it more effective to prioritise regional-scale tipping points.

From a Research perspective, the PBs yet to be quantified, as well as the highly uncertain PBs, represent gaps in knowledge and should be prioritised.

What PBs don't tell us 

Since the PBs became influential in global sustainability policy development, many scholars have proposed supplementary or alternative PBs, and critiqued the PBs.

(Source: Science, 2012)

For instance, this paper suggests an alternative PB, terrestrial net primary (plant) production (NPP), a global measure of biosphere production humans are consuming for food, fiber and fuel. Present human appropriation is at 40%. 6 out of 9 PBs either are incorporated in or influenced the NPP.

This paper criticises the PBs for downplaying the urgency of Freshwater Use problems.

This paper questions the relevance of a global perspective for Biogeochemical Flows from a governance perspective. It may be more effective to address transgressions from a regional perspective.

Nevertheless, most see the usefulness of the concept.

Justification for Planetary Boundaries

To quote Rockström on the PB MOOC, there are 9 environmental processes that "science now believe" qualify as PBs. He appeals to the authority of an arbitrary, seemingly objective, arguably masculinist "science".

Feminism aside. What is science actually saying?

One characteristic that set the PBs aside from earlier sustainability science concepts like ecological footprints and limits to growth, is its focus at the biophysical level of the Earth System's resilience, without making assumptions on either human needs or human innovation capacity. This means that it is fundamentally science-driven, instead of socially-driven or politically-driven, although it has implications on society and politics to mitigate threats. 

Firstly, how were the PBs selected, and how was this justified?

1. Climate Change
Acknowledging that the stable Holocene climate enabled human flourishing, it makes sense for climate to kickstart discussions about safe environmental limits. There are many negative feedback loops, such as the ocean solubility pump, which regulate climate and promote equilibrium, but there are also many positive feedback loops, such as the ice-albedo effect, which may create runaway effects and irreversible change. We must thank the lifeless Venus, which took on a very different climate trajectory, for providing concrete evidence for the runaway greenhouse effect.

The Carbon Cycle (Source: NASA)

2. Ocean Acidification
Oceans have planetary-scale tipping points. Due to the increase in atmospheric CO2, concentration of free H+ ions in the surface ocean increases, lowering the saturation state of aragonite, quantified as Ωarag. At Ωarag<1, aragonite dissolves: a clear tipping point, because aragonite forms naturally in almost all mollusk shells.

3. Stratospheric Ozone Layer
The Stratospheric ozone layer in the upper atmosphere experiences the ozone hole phenomenon, a classic example of a tipping point. It is important for maintaining the stable state of the biosphere because it shields the entire biosphere from harmful solar ultraviolet radiation, which can harm animals and plants and kill bacteria, fungi, and phytoplankton on the surface of the Earth.

(Source: Eco-Globe)

The experts also identified 6 processes that qualify as PBs but do not have planetary-scale tipping points. Still, they fulfill the PB criteria for 2 reasons. Firstly, they determine whether the large-scale processes would cross tipping points. For example, land use systems and freshwater use, are fundamental in providing the capacity for land areas to be carbon sinks. If that capacity is not there, the climate system will very rapidly cross the tipping point. Secondly, they regulate sub-planetary scale tipping points. For instance, biodiversity loss is increasingly shown to have ecosystem-scale tipping points. In the Anthropocene, we risk having tipping points crossed in so many places around the world simultaneously that they aggregate into planetary-scale impacts.

4 biosphere processes with sub-planetary scale tipping points were identified:

4. Biogeochemical Flows 
Global Phosphorus and Nitrogen cycles link the living (bio) and the non-living (geo) parts of the Earth System.

5. Freshwater Use
Water regulates the amount of biomass, which regulates the amount of Carbon in the Earth System.

(Source: Nature, 2016)

6. Land-System Change
Renamed from "Land-Use Change" in 2009, land systems are the fundamental fabric for all living species on Earth. This PB focuses on land surface–climate coupling: biogeophysical processes in land systems that directly regulate climate.

(Source: Nature, 2014)

7. Biodiversity
The genetic diversity of organisms determines the overall ability of the biosphere to adapt to changing conditions. In the 2015 update, this PB was renamed "biosphere integrity", and branched out as genetic diversity and functional diversity. Genetic diversity is easier to define and quantify. Quantifying functional diversity has been developed at local scales, but not yet on global levels.

(Source: Nature, 2004)

They also identify 2 boundaries that are heavily anthropogenically caused:

8. Atmosphere aerosol loading
This describes the amount of soot and pollutants in the air. This is related to the biosphere in that it regulates the stability of large rainfall systems, such as the Monsoon. At present, only one regional boundary (south Asian monsoon) can be established for atmospheric aerosol loading. Aerosols (highlighted in red below) are also components of Radiative Forcing, producing a net cooling effect on climate.

(Source: MOOC)

9. Novel entities
This was referred to as chemical pollution in 2009. In 2015, this was provided as "new entities", and stems from increasing evidence that the cocktail of chemical accumulation and modified life forms in the biosphere could potentially cause major shifts in life conditions on Earth, such as plastics and the genetic composition of species. There is not yet an aggregate, global-level analysis of chemical pollution on which to base a control variable or a boundary value.

(Source: Ocean Health Index)

Skeptics argue that these scientists made an arbitrary, but reasonable, decision on which processes to select as PBs. However, the framework is very useful as a springboard of additional ideas and improvements. The SRC itself is also constantly seeking to improve its research, revising the original PBs in 2015.

(Source: Nature, 2009)

(Source: Science, 2015)

With today's greater interconnectivity and educational resources becoming increasingly made available online, MOOCs are a great way to learn. I found this MOOC clear, thought-provoking and informative.

Within the 2015 paper, there is uncertainty about how or whether PBs can be usefully and/or accurately quantified, what "transgression" means or will lead to, and the hierarchy of the boundaries. I will discuss this in my next post.

Motivations Behind Planetary Boundaries

Imagine a teenage girl, trying to figure out what to do with her life, reading up about sustainability. 

That was how I discovered the PBs concept back in 2013. I was completing the Age of Sustainable Development, Professor Jeffery Sach's MOOC (Massive Open Online Course), which brought together many sustainability concepts that left an impression upon me, including the PBs. 

So of course, being a teenage girl, I had to project my internal existential crisis onto the external planetary crisis, and decide that solving this crisis was to be my sens de la vie.

(The existing term MMORPG gave rise to the acronym MOOC.)
(Teenage girls also play too much computer games.)

My interest in PBs resurfaced in the first lecture of this module.

In an effort to learn about PBs, I enrolled in the SDG Academy's Planetary Boundaries and Human Opportunities MOOC, presented by Professor Rockström himself. The SDG Academy is the online education initiative of the Sustainable Development Solutions Network of the UN.

A screenshot of the SDG Academy dashboard, with many MOOCs to choose from.

My first impression of the MOOC was that it uses many words to explain something very simple. There was more focus on big picture ideas than explaining the actual PBs. There are also minor inaccuracies, such as when Rockström categorised atmospheric aerosol loading under a biosphere process although it should be an anthropogenic change. Nevertheless, it expands on the original papers in an engaging manner.

The MOOC begins by considering the challenge of sustainable development.

The modern thinking around sustainable development revolves around 3 main pillars: social, economic, and ecological. The PBs concept challenge this notion, putting forward evidence that sustainable development rests on the precondition that we are operating within safe, resilient life support systems. Thus, it persuades world leaders to prioritise the ecological aspect and become planetary stewards of human well-being.

Earth is under pressure from a quadruple squeeze from Affluence and Population, the Climate Crisis, the Ecosystem Crisis, and "Surprise": the increasing risk of abrupt, unpredictable, and irreversible changes. The below diagram illustrates what, in contrast with self-regulating stability, an irreversible "tipping point" would look like. But what is this critical point?

But what is this critical point? What state is considered "safe"?

The figure below shows the 18-Oxygen to 16-Oxygen isotopic ratio in the last 100,000 years.

A figure of the last glacial cycle of 18-O and selected events in human history. (Source: Ecology and Society)

Oxygen isotopic ratios are strongly correlated with global mean temperatures, because of mass-dependent fractionation of oxygen isotopes in water in the Hydrological Cycle. The isotopic signatures are preserved in ice cores, which lock away more ice when global temperatures are colder. This data gives a reliable indication of the rise and fall of global mean temperatures, with peaks representing interglacials and troughs representing glacial periods.

Compared to other events in human history, characterised by frequent ups and downs, resulting in the labeled mass migrations, the current Holocene interglacial period that began 10,000 years ago has seen extraordinarily stable climate. This relatively stable environment allowed agriculture and complex societies, including the present, to develop and flourish. This is the stable, desirable state that we want to preserve.

(Source: ShortHistory)

What are the environmental processes that allow the Earth to remain in this stable state? Living in the Holocene, we have a good understanding of present biophysical conditions. In my next post, I will look into what environmental processes were chosen as PBs.