Synthesis and progress on planetary boundaries
The science on planetary boundaries builds on the remarkable advancements in Earth system science over the past 20 to 30 years. It’s an integration in the natural next step in scientific advancement between our understanding of the pressures of the Earth system, how the Earth system is a complex self-regulating biogeochemical physical system, and the recognition that if we push environmental systems too far, we risk crossing tipping point that can fundamentally, abruptly, and irreversibly push ourselves away of the stable desired state of planet Earth.
What may surprise you is that the approach of finding planetary boundaries is illustrated very nicely in this first slide here where a Moon lander is looking at our wonderful, small, little marble Earth planet from a distance.
In fact, that’s how the analysis starts. We step out as humanity and try to understand the Earth system and ask ourselves to question what are the Earth system processes that regulate the stability and the resilience of the Earth system? And for each such process we ask ourselves what is the boundary beyond which the system could be pushed outside of a desired state?
And science shows very clearly that we know what this desired state is. And in this slide as a synthesis of that shows the ice core data from Greenland indicating the enormously jumpy ride that humanity has had throughout his entire period on Earth as modern human beings.
This graph shows our last 100 000 years journey on Earth, until we enter the final, last interglacial period, which we learned in school to call the Holocene, which I would call the Eden’s Garden, the perfect paradise, desired conditions for us to build our civilizations and the modern world as we know it.
So the planetary boundary framework is about safeguarding the desired Holocene-like state on Earth by recognizing this state as the only state we know that can support the modern world as we know it, and from science determining the Earth system processes that regulate this state.
And that is what led us to defining the nine Earth system processes that we know, with the best science at hand, regulates the stability of the Earth system.
And here we have of course the big systems with large scale tipping points, such as: climate change, ocean acidification, stratospheric ozone depletion. We have the four slow variables that operate under the hood of the Earth system regulating the ability of the large systems to be stable: land system change, fresh water use, the rate of biodiversity loss, and the way we interfere with the large nutrient cycles of nitrogen and phosphorus. And then we have the two processes that are so highly manmade: namely aerosol loading, which is all the soot and the particles in the atmosphere that cause large health challenges but also influences, for example, rainfall patterns and weather conditions; but finally of course the novel entities, the exponential growth of chemical compounds that aggregate themselves in the Earth system.
By tapping on the best science we can put quantitative boundaries that gives us in green a safe operating place. This is where we can put humanity back, to prosper, develop, evolve, and thrive within this safe operating space. That’s why planetary boundaries is a truly integrated analysis. It’s about a safe space, and by biophysical terms, but it’s about recognizing equity, fairness, and a just distribution of the remaining ecological space on Earth to enable a world of soon 9 billion people to develop and prosper.
In my mind this is the new definition of sustainable development. It’s recognizing that global sustainability and development within a safe operating space is the new endeavor and the new goal for human development on Earth.
We’re very excited by the fact that science can now step up to, I would argue, the responsibility of providing quantitative global environmental goals of this kind. It shows in our analysis that we’re already in a danger zone on climate change, biodiversity loss, and interference with the nutrient cycles.
This work was released the first time in 2009, and has since then led to a very large, vast set of scientific efforts of critically analyzing the quantifications, critically asking the questions whether we’ve got the nine boundaries right, and based on all the science we are working continuously updating this concept to get the absolutely best quantifications.
And a few exciting updates have occurred based on scientific colleagues around the world publishing updated work in this area. The first one is the recognition that the nine boundaries are not entirely, so to say, even in the role of regulating Earth resilience.
In fact we do identify now that three of the boundaries are what we call core boundaries. They operate and regulate the entire Earth system, and they are the endpoint depending upon how the other boundaries operate.
So the best example of these three core boundaries is climate change. Climate change is the end result of how we manage fresh water, nitrogen, phosphorus, land, biodiversity, oceans. It all aggregates up into the functioning of the climate system. So when we use climate forcing as a good control variable for the climate system, the level of that forcing, whether or not we stay within the boundary, depends intimately whether we’re able to stay within a safe operating space for the other boundaries, to the extent, in fact, that among us scientific colleagues we talk of the boundaries as being like three musketeers, “One for all, all for one.” It seems we need to stay within a safe operating space for every boundary in order to avoid that one boundary flips over across the threshold.
The other core boundary is biodiversity. We now recognize increasingly that the genetic diversity on Earth, and the functions they play to sustain resilience and to build human well being, is a high level aggregate result of how we manage fresh water, land, oceans, nutrients, and even the climate system.
And the third core boundary we believe is novel entities. The reason for this is that chemicals, such as everything from endocrine disruptors, persistent organic polluters, all the way to nuclear waste and loading of heavy metals, is so totally lien to the operations of the Earth system, in fact the Earth system has never seen, at least not in millions of years, the kind of human-induced artificial loading of new totally artificial compounds into the Earth system.
We’re learning as we speak what the aggregate effect of these can be on our own health, on the genetic composition of species, from birds to humans. But this is an entity of its own core right. And these three we call core boundaries.
The second development is that we’ve refined the biodiversity boundary. We call it now biosphere integrity, because we recognize that genetic diversity is one thing which we captured in the first analysis. Basically what’s the number of species on Earth, which we can measure quite well with extinction rate, which you used in the original analysis.
Now we’re much more, let’s say, sophisticated in using a new index called the biosphere integrity index, which measures not only number of species but also their functions and how many species within each function. So we can secure, for example, that we do have the minimum amount of pollinators in an agricultural landscape. And this is truly exciting giving the tools for sustainable development in the Anthropocene.
We’ve also refined some of the quantifications. And I would just like to share a few of the key developments here. And the number one is on phosphorus. In the original analysis, we were preoccupied with how much phosphorus can we load into the oceans before we risk a large scale tipping point in the oceans into anoxic, oxygen-free dead states in the ocean?
We were criticized for this. Scientists pointed out that way before you’ve pumped in so much phosphorus in the ocean that you could tip the ocean you’ve destroyed so many fresh water systems along the way of the journey of phosphorus from where it’s loaded, often in an agricultural field, to the ocean that we have tipping points occurring in fresh water systems. So now we actually have a twin definition of the phosphorus boundary.
One, which we maintained from the original analysis, which is the amount of phosphorus that we can load in the oceans. It emains in fact eleven million tons of phosphorus per year. We’re today loading eight, nine so we’re approaching the boundary. But can you imagine? The analysis shows that already at averaging at 4 million tons of phosphorus per year on what we call erodible soil, which is essentially how much phosphorus we can load on productive agricultural land, when we go beyond that number we risk large scale tipping points in fresh water systems. These twin boundaries need to be considered for phosphorus.
For nitrogen finally we took, which was a very wise decision, the valve of how much inactive nitrogen we can maximum take out of the atmosphere, and transform into reactive nitrogen which would plug into the biosphere. You may be aware that the fantastic invention of the Haber Bosch process, which produces reactive nitrogen fertilizers is the vehicle for our modern agriculture, without which we probably could not feed ourselves in the modern world. But it loads reactive nitrogen into the biosphere at an extent, which is so large that we humans are now a much larger force than the entire global natural nitrogen cycle.
We estimated in the first analysis that the maximum loading of nitrogen in order to avoid that nitrogen triggers tipping points in ecosystems was 35 million tons of nitrogen per year. It was a first best guess. Roughly one-fifth of the amount of nitrogen that we’re taking out of the atmosphere, so a dramatic decrease, and therefore indicating that we’re way out in a danger zone on nitrogen.
However, we did, you could argue, a simplification in the first analysis, because you see there’s another way that we humans take out nitrogen from the atmosphere, which is by cultivating nitrogen-fixating crops. So, we have also biological fixation nitrogen actively induced by us humans in modern agriculture. Now we have included that, so now we have a boundary that includes both the industrial uptake of nitrogen from the atmosphere in the industrial production of fertilizers, and the additional human-induced nitrogen fixation by, for example, legumes in modern agriculture. And together that forms a much more robust boundary, which ends up being an estimated 44 million tons of nitrogen as a maximum boundary per year.
I won’t go through the rest of the boundaries. I really urge you to look at the analysis and the materials that come with this lecture. But I really want to close by emphasizing that every boundary has an uncertainty range. And the uncertainty range is often quite large. It’s the humble reminder that science continuously adds new knowledge, and that the boundary position is proposed at the lower, more precautious end of that uncertainty range, because we now, as for ozone, that we always are facing surprise when it comes to the large changes we’re seeing in the Anthropocene.
Overall it’s also important to recognize that even though we have attempted to quantify boundaries for the nine boundary processes at the global level, they do operate across scales, and they do interact across scales. We’ve done some very significant updates in terms of downscaling those boundaries that are relevant to downscale, and these include, for example, the coupling of a global boundary, on fresh water with the river basin definition of minimum amounts of environmental water flows.
The coupling of the phosphorus boundary for fresh water, with a maximum amount of phosphorus per hectare of land that we can allow ourselves to apply. Same for nitrogen, taking it down to the hectare level.
These are really exciting developments which enable the planetary boundary concept to be operational also at the local level, for a business, of a community, or of a nation’s policies in terms of how to contribute to stay within a safe operating space. And that is in my mind one of the biggest advancements in the work we’ve done in the planetary boundary analysis over the past five years.