The Planetary Boundaries Framework
Introducing The Planetary Boundaries Framework, first proposed by Professor Johan Rockström and his colleagues in 2009. Based on Rockström’s most recent work I’ll run through how the framework can help tell the story of our planet and human influence, why we need to act now to prevent irreversible damage, and other considerations we need to make when applying a solutions lens to the climate crisis.
“We must become stewards of the planet”
The scientific community largely agrees that for thousands of years, the planet has existed in a stable state known as the Holocene which supports humanity as part of the complex biosphere on Earth. As a result of human activities, researchers now argue we are entering (or already in) a new distinct period deemed the Anthropocene. The Anthropocene refers to the current geological period, in which human activity has been and remains the dominant influence on the climate and the natural environment.
Anthropo – Greek term for ‘human’
Cene – ‘new’ epoch when referring to geological periods
In 2009, Rockström and his colleagues first developed The Planetary Boundaries Framework. The framework details 9 processes that occur on Earth (climate change, biosphere integrity, ocean acidification, land system change, freshwater change, biogeochemical flows, atmospheric aerosol loading, stratospheric ozone depletion and novel entities) and their ‘safe operating zones’, which support the existence of humanity. Most recently, these researchers have quantified the degree to which the ‘safe zone’ is being exceeded for each process, as a result of human activities.
The safe operating zone recognises that in response to changing environmental pressures, the Earth systems operate in a predictable manner up to a threshold, beyond which these responses can become non-linear and abrupt.
When it was first proposed in 2009, 7 boundaries were assessed and only 3 deemed to be beyond their boundaries. In 2015, a second update was provided by which point human activities had pushed climate change, biodiversity loss, shifts in nutrient cycles (nitrogen and phosphorus), and land use beyond their boundaries into unprecedented territory. In 2023, all 9 processes were able to be quantified for the first time. Over this period of time, it has become evident that human activities are pushing many of these processes well beyond their safe operating zone.
Stockholm Resilience Centre, 2023
The increase in (destructive) human activities have dramatically modified the planetary processes that support humanity’s existence. In 2023, Rockström and colleagues published that 6 of the 9 processes currently exceed their quantified safe operating zone (as shown above). Stratospheric ozone levels have slightly recovered as a result of collective global action however the remaining 8 are getting progressively more dire. Biosphere integrity and novel entities (synthetic chemicals etc.) are currently the furthest from their stable states, with many of the other processes following this trend. Additionally, of the 3 within their safe operating zone, both ocean acidification and atmospheric aerosol loading are quickly moving towards their respective boundaries.
Last September (2023), I attended the 44th TB Macaulay lecture in Edinburgh where Johan Rockström spoke. The theme for the lecture was ‘a safe and just future for humanity on Earth’. Rockström himself warned that we are at a tipping point after which we do not have a roadmap.
At the lecture, Rockström introduced the concept of a ‘phase shift’. A phase shift occurs when an external pressure (in this case, human activity) is applied to an environment. As a result of this pressure, the environment reaches a ‘tipping point’ where it is pushed from one stable state that supports a particular community of organisms, to a different stable state. This alternate stable state is often unsuitable for those that thrive in the initial one.
Phase shift illustration by OCC
Importantly, once shifted into a different stable state, it is uncommon to return to the original state. This is the challenge we are facing when the planetary boundaries are pushed beyond their safe operating zone. It becomes difficult to predict what impacts pushing these processes beyond their known boundaries will have. In the meantime, we face a tumultuous transition period in which previously predictable processes function in an unpredictable way.
The good news is we can change things with collective action. This is most strongly demonstrated in the story of stratospheric ozone depletion:
In the 1970’s, the global scientific community realised that the ozone layer (effectively a sun shield in the atmosphere that protects us from ultraviolet radiation) was being rapidly depleted due to the high use of ozone depleting chemicals in everyday products such as aerosols. So much so that there was a hole in the ozone layer over Antarctica. Collective advocacy and political willingness meant the use of these chemicals was limited in order to restore the ozone layer.
It worked. Stratospheric ozone depletion is the only planetary boundary to have improved since they have been measured. With 99% of these chemicals removed from circulation, the ozone hole is expected to close by the 2060’s.
The tricky part is that we can no longer adopt simple, straightforward solutions that address individual boundaries.
In his lecture, Rockström detailed the research developments made in the planetary boundaries space, emphasising that the interplay between these processes means increased difficulty in predicting future trends. He highlighted the interconnected nature of these elements means that as they are individually pushed beyond their limits, they have the potential to accelerate change in the other boundaries. His team’s recent paper ‘Earth beyond six of the nine planetary boundaries’ emphasises the importance of considering these boundaries as they interact with each other as opposed to in a siloed manner. We need considered, thoughtful steps in the right direction and we need to be monitoring the effects of the changes.
Hope is not lost, and while it is an urgent and large challenge we’re facing, finally having a much clearer picture of how human activities impact the planet is a crucial first step in the right direction. As Rockström and his colleagues argue, the latest update to the planetary boundaries framework is a needed wake-up call for us that our home is at high risk of leaving its stable state. The research provides hope, emphasising that a better understanding of the state of play will aid in stimulating innovation and ensure the Earth’s planetary boundaries are safeguarded in the future.
