Now that we’ve identified the nine planetary boundary processes, the large scale processes of climate change, stratospheric ozone depletion, ocean acidification, the slow variables of rate of biodiversity loss, interference with the nitrogen and phosphorous cycle, land use change, freshwater use, and the two heavily human-induced risks around chemical pollution, aerosol loading, the challenge arises of defining quantitatively the boundary position for each one of these processes which distinguishes between a safe operating space and entering a danger zone where we have a higher probability of crossing tipping points which would take us away from a safe Holocene state.
So for climate change, for example, it falls naturally to choose the concentration of greenhouse gases, and for each boundary we do the same.
And once we’ve identified a control variable, we try with the best of our knowledge to identify the point at which science indicates that we approach and are at risk of crossing a tipping point.
And that’s the way we pursue for each of the boundaries the exploration of positioning the quantifications of a safe operating space for humanity within the Holocene state. And the theory here is relatively simple but fundamentally important. And it’s shown in this graph of our – where we distinguish between the safe operating space in green, an uncertainty zone or a danger zone in yellow, and entering a zone of danger in red.
So what we’re doing for each boundary process is one, trying to identify a control variable which is a good indicator or proxy for the stability of a system.
So for example for the climate system we’ve identified climate forcing in – defined in the number of watts per square meter of increased heat in the atmosphere, and also carbon dioxide concentration as two good control variables for the climate system. And then we scan off all the scientific literature to try and – and explore what does science say today about the point beyond which, in terms in this case concentration of carbon dioxide, we may risk abrupt and irreversible tipping points which could push the Earth system outside of an Holocene-like state.
But the trick is that science of course is associated with large uncertainties, and will always continue to be associated with uncertainty, not necessarily only because we don’t understand the climate system in exact system but because all planetary boundaries interact to a point where it’s extremely complicated to put an exact point at which you cross a tipping point.
That causes and generates what we’ve called a zone of uncertainty, essentially a standard deviation in science. And that zone of uncertainty is the zone of uncertainty within science defined here as the yellow range. And somewhere in that yellow range we, with a very high probability, have the threshold, the point where the system crosses a tipping point.
Now here the planetary boundary theory takes its first and only normative stance. We have decided as a proposition in the planetary boundary framework to position the boundary at the lower end of the scientific uncertainty. This is applying a precautionary principle.
I mean you could, theoretically at least, place your boundary at the upper end of the uncertainty zone and – and rather have a more optimization-based approach. But we feel that it’s a very risky approach to take because we fear that somewhere in that yellow zone science indicates that we have thresholds that – with a very high likelihood will occur.
So the boundary position is at the lower end, and that gives us the green space below, so to say, when we stay below the control variable position we’re in a safe operating space. The upper end of the uncertainty zone then performs the threshold between the zone of uncertainty and a clear zone of high danger.
And that gives you the three positions in this graph, a safe operating space, an uncertainty zone, and a point beyond which we are a very high risk of crossing tipping points.
The reason why we have shown two graphs here is that for the systems where we have large scale tipping points we do try to explore exactly the point at which we had evidence of thresholds.
But for those processes such as land system change or fresh water use where there’s no evidence of planetary scale tipping points the change when we, for example, start overusing water or degrading land is that the system gradually becomes more and more degraded.
The response of the system is not associated, at least not as we know, with an abrupt threshold. What we try to identify then is the point at which evidence suggests that if we push the system even further, if we cut down even more forest, the feedback into for example the climate system is such that it could push the climate system across a tipping point. And that then becomes the point where we put the boundary.
So we have one set of boundaries defined on the point along a control variable beyond which the feedbacks can damage other systems, and for those systems which have thresholds we put the boundary at the point beyond which we actually can have a threshold.
So that is the fundamental thinking around planetary boundary theory, and I would very much encourage everyone to look at the literature around this which explains this very clearly.
Now what’s then the result? Well the result is in the following graph showing the nine planetary boundaries which when quantified, and in the original publication we made attempts of quantifying seven of the nine boundaries, we felt that we did not have evidence enough to quantify either the aerosol loading boundary nor the chemical pollutions or novel entities boundary.
But for this– the remaining seven we proposed quantitative boundary levels which they creates the safe operating space you see here on the graph.
And our original analysis showed that for three of these boundaries, which is indicated in the – in the red areas here which define our current state for each boundary, that we have transgressed and entered the danger zone for climate change, the rate of biodiversity loss, and the human interference with the global nitrogen and – for the global nitrogen cycle. In fact for phosphorus we estimate that we’re still within the safe operating space.
So this is to illustrate the way we can apply planetary boundary thinking, that if we can use science to define the boundary levels beyond which we can push the system outside of a stability domain we can actually monitor and keep track of where we are with regards to all the boundaries.
Now I really want to emphasize finally that because we are beyond a safe operating space for, for example, climate does not mean that have crossed the tipping point, it just means that we’re in a zone where we can potentially see tipping points occurring.
And unfortunately the observations we’re making, for example, both on biodiversity, climate and certainly on nitrogen, is in fact that we are inducing tipping points and potentially also have the start of irreversible change at the larger scale.
Now these estimates are all summarized scientifically in quite substantive scientific tables which are provided in the literature which is associated with the course we’re giving.
So I would very much encourage anyone to, say, following this lecture to also explore in more detail the contents and the quantifications as presented in the original table that we have in the 2009 publication, and I’d also like to flag that we’re right now currently, in August 2014, working on an update of a planetary boundary 2.0 which will provide the scientific update on the quantifications of the boundaries, a certain amount of refinement of the boundary definitions, and even attempts to quantify those unquantified boundaries which we had in the 2009 analysis.
Now in the final graph here you see the numbers that we had in the original publication. And you see here the – the boundary position, but also the uncertainty range which is then the uncertainty range in science.
And what you see here is, for example, estimates which for climate change is actually quite robust, or very robust, in terms of scientific evidence, that when we pass a concentration of carbon dioxide of 350 ppm – we are today at 398-99 – we enter a danger zone and we’re starting to see evidence of abrupt changes in both Greenland, inland glaciers, ocean acidification related to climate forcing, and changes in Antarctica.
Then we have a few boundary definitions which are more tentative. For example on nitrogen the definition we took at the original analysis was set at maximum amount of uptake of nitrogen from the atmosphere for fertilizer of thirty-five million tons of nitrogen per year.
That is roughly one-fifth of our current uptake from the atmosphere. Humans are the largest interference of the global nitrogen cycle, all categories. In fact our modern agriculture takes out more nitrogen in the atmosphere than the entire biosphere does naturally.
This number is based on a first best guess, and we’re working very actively to update this, but it shows at least that we’re able to take the first stab at identifying what are the safe boundary levels even for such complicated processes, which clearly are key for the resilience of the Earth system, in terms of defining quantitative safe levels.
And the science is – is advancing as we speak. In fact since the 2009 publication there’s a very, very broad set of fantastic, uh, groups of scientists who have critically assessed these first numbers and improved them, and in almost all instances come up with even better, um, proposals of quantifications, and that synthesis is – is something that we’re building on to continue [to] develop this framework, which increasingly has a very strong resonance out in both science, policy and business, and therefore also in its application in different sectors of society.