I’m going to talk about the interactions between the planetary boundary processes.

The planetary boundaries framework brings together the best of our current scientific understanding about a very large number of complex interactions in the Earth system. The boundaries are the precautionary limits that we think society should set about how to deal with biological, chemical, and physical regime shifts and thresholds that may happen in the Earth system.

The science is progressing on all of the different boundary processes. Since 2009 when the original framework was published we’ve been working, as a scientific community, on all of the individual aspects.

The image that you see in front of you is a representation of the boundaries for the current regime of the Earth system with our best available knowledge for each of the processes. But in this figure we’re still treating the processes really as if they acted independently.

One of the major areas for research at the moment is to better understand the interactions between the physical and the ecological processes that are happening on planet Earth.

Earth system interactions are complex and dynamic. If you change one dimension the others will change in response.

In this figure we’re trying to represent the fact that if you approach any one of the other boundaries, you increase the pressure on the ecosystems that make up biosphere integrity. So for instance, as we approach the climate change boundary it’s likely that there will be more pressure on the world’s ecosystems, and that reduces the safe operating space for ecological change. The same is true, although the strength of the arrows might be different, for all of the other processes. If you interfere with one of the planetary boundaries you will see the consequences in the others, because the Earth system connects these processes in complex ways.

If you exceed one boundary it’s likely to have cascading effects on the other boundaries. And at the same time if you remain within one boundary it does not remove the pressure on the others either. The mechanism for these cascading effects is really the fact that we’ve got complex feedbacks that link the different components of the Earth system.

In other words, the feedbacks between land, atmosphere, oceans, and the living organisms that make up the biosphere. Some of these feedbacks are also relatively well understood. Here we have an example of a positive feedback that links land use and the water cycle. This is a feedback that’s been very well understood. It was first proposed nearly forty years ago, where processes, like deforestation and decreased vegetation cover, changed the reflectivity of the Earth’s surface. That changes the way that the climate system works, it changes the temperature of the atmosphere, changes the distribution of clouds, and you tend to have less rainfall, which reinforces the original problem. This is a positive feedback because it reinforces the original driver of change. If you decrease vegetation cover you tend to get less rain that leads to an even stronger decrease in vegetation.

We also have negative feedbacks that tend to damp down the initial pressure on the system. We are beginning to understand the interactions between climate and biosphere, and here again we have an example. If we cause deforestation we remove the capacity of living organisms to take up CO2 through photosynthesis. That weaker CO2 uptake leaves more carbon dioxide in the atmosphere, because CO2 is a increase the warming of the atmosphere. Most vegetation responds to a warmer temperature by increasing its growth.

So in this case by reducing vegetation in the first place ecosystems will tend to respond by increasing their biomass production. Now obviously this kind of feedback is really important in balancing environmental changes. Negative feedbacks help to keep the Earth in balance in a particular regime. But they don’t go on forever. Vegetation has an upper limit to its temperature tolerance, and so as we increase temperatures we will also see an increased risk for abrupt changes when these negative feedbacks break down.

This research on feedbacks, especially the feedbacks with climate change, [is] a major research interest all around the world at the moment. This figure shows a summary of some of the work that’s happening around the world that was published in the most recent Intergovernmental Panel on Climate Change and its assessment report.

You can see that these feedbacks are highly complex. And again they link atmospheric processes, land cover processes, the water cycle, and of course the climate change itself.

Analyzing the interconnections between boundaries is an enormous challenge because it requires scientists to work across what have normally been disciplinary boundaries. The people who’ve got real expertise in atmospheric chemistry and physics tend not to have such deep understanding of the biological and ecological processes that are happening at the ground surface. We use different language, we use different models and tools, and so this is probably the main global collaborative adventure for research at the moment.

It isn’t just a question of understanding the physics and chemistry and biology of the planet, however. Because these processes all have human drivers it’s also requiring us to have new interactions with researchers from across all disciplines, and with policymakers, with businesses, and with people in civil society. You may already know about some of the movements for community science.

If you see any we really recommend that you engage with them, because a major challenge to understand the interconnections is to move from the global abstract picture that we have of the boundary processes to the rich understanding that we need in order to be able to understand and represent in models and to respond to the issues that play out at local level. In many of the discussions about the planetary boundaries we are dealing with a very abstract global picture, but the consequences and the causes, the human causes, almost all play out very locally. So we have a spatial challenge to deal with as we deal with the interconnections as well.

One approach that we’re taking to this, because it is enormously difficult to connect everything with everything else, we’re focusing on what we call nexus approaches that let us look in depth at some of the interactions.

So for instance, nexus where we have very good analytical tools and a substantial amount of data on changes at the global and the local level, is the interaction between the energy system, physical climate system, and the water cycle.

Again, this nexus work isn’t just science happening in isolation, it’s science happening in direct dialogue with policy and the decision makers that affect these different contexts.

Another important example of our nexus approach is in our understanding of the interactions between food production systems, biodiversity and ecosystem change, and many aspects of pollution. Nutrient enrichment is one example, but also the chemical pollution associated with industrialization, agricultural production, and urbanization.

You can see that these are very complex problems, many people call them wicked problems. The challenge is that it’s not just a scientific issue, although we have an enormous need still for basic data on all of these various dimensions.

It’s about how science interacts with wider society. We need to have better dialogue between scientists and the decision makers all across society that deal with the different sectors that are contributing to the problem.

Another challenge is that we can’t treat it as if we were outside of the system. We are in the system that we ourselves are changing. We’re responsible for the causes and we will feel the consequences.

We aren’t just changing the variability of the processes, we’re changing the whole risk spectrum because we’re altering the feedbacks themselves. And so this requires us to treat the problem with more urgency than any we’ve ever seen before. And although these are global problems we can only deal with them in our own place, in our location, in our academic discipline, or our profession, whatever that may be.