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.