Figure (from Steffan et al. (2015) Science, 347, issue 6223 #1259855) illustrates the current status of the control variables for seven of the nine planetary boundaries. The green zone is the safe operating space (below the boundary), yellow represents the zone of uncertainty (increasing risk), and red is the high-risk zone. The planetary boundary itself lies at the inner heavy circle. Control variables (see text below) have been normalized for the zone of uncertainty (between the two heavy circles); the center of the figure therefore does not represent values of 0 for the control variables. Processes for which global-level boundaries cannot yet be quantified are represented by gray wedges; these are atmospheric aerosol loading, novel entities, and the functional role of biosphere integrity.
Conceptually, planetary boundaries (PBs) define a safe operating space for humanity determined by the state of key biophysical processes that combine to regulate the stability of the Earth system. As the above figure from Steffan et al (2015) indicates, some of the nine PBs that are commonly referred to and their linked control variables (measurable parameters that represent the state of the PB) are relatively well-understood. For example, climate change and atmospheric CO2 concentration, and biogeochemical flows and nitrogen fixation rates. In these cases, the PB concept could be claimed to be having an influence over policy-making, for example in the setting of caps on CO2 emissions in order to mitigate climate change. Much uncertainty concerns the other PBs, however. Notable among these are novel entities (NEs), or new substances, new forms of existing substances and modified life forms that have the potential for unwanted geophysical and/or biological effects.
A paper just out (Persson et al. (2022) Environmental Science and Technology, 56: 1510-1521 – a publically accessible version of which is available below) reviews the scientific discussion centred upon attempts to define and quantify the PB for NEs, focusing in particular on plastic pollution as a component of chemical pollution. Chemical pollution generally is of particular concern because of a huge uptick in the production and release of a broad range of chemicals, including plastic, over the last 70 years or so. Global production of chemicals has increased 50-fold since 1950 ~ today there are an estimated 350,000 chemicals and mixtures of chemicals available to buy. We know very little about the long-term exposure risks of the vast majority of these and virtually nothing at all about potential synergistic effects nor their ability to bioaccumulate and biomagnify through the food chain. The vast majority of chemicals now in production have a synthetic origin – they do not naturally occur. Therefore, unlike control variables for other PBs such as CO2 and nutrients, there is no “natural” baseline against which to compare current levels and trends. We therefore have no idea just how much NEs the Earth system can withstand without a major shift towards a new operating state that in all likelihood will be less suitable (or “safe”) for humanity and the ecosystem services we are dependent upon. In other words, we have no idea where the tipping point for NEs might be.
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Open in new tab Trying to control releases of one harmful chemical often simply results in increased releases of another chemical if the need for the non-harmful properties of the original chemical remain – the so-called “lock-in” effect. The lock-in effect becomes particularly serious when the replacement chemical subsequently turns out to be equally if not more harmful than the chemical it was designed to replace. The production and use sequence of CFCs, HFCs and HCFCs is an example of this. Lock-in effects also relate to our use of resources. Thus CO2 and plastics are both products of our use of fossil fuels (CO2 emissions result from our burning of fossil fuels, whereas 99% of the materials that go into plastics are from fossil fuels). If we reduce our burning of fossil fuels to generate power, thereby reducing CO2 emissions, will the fact that we are locked-into (economically dependent upon) a fossil fuel industry mean that the latter will start to invest even more in encouraging the use of (and therefore the need to produce more) plastic, thereby increasing plastic pollution? How do we avoid this lock-in effect?
The paper introduces the concept of an “impact pathway” and its use in defining control variables for NEs. There are major differences between countries in their abilities to monitor and manage production and releases of NEs. Even in technologically advanced countries, however, the current rapid growth in the production and release of NEs into the environment massively outstrips our ability to assess the ecological and human health risks posed. Given that we know so little about the impacts of NE releases and how much the Earth system can cope with, the authors of the paper argue for a precautionary approach to what is a transboundary, global problem. Just as we have developed and implemented policies aimed at net zero emissions of CO2, we need – the paper claims – to at least cap emissions of NEs at levels below tipping points in the Earth system. In order to do this, we need research on where those tipping points might be and how they might vary as a result of, for example, climate change.
Rather than just investing in the invention and production of new chemicals to meet our ever increasing needs, we also need to start investing much, much more in how existing and new chemicals are impacting and likely to impact ourselves and the world we share.