What are the safe and just boundaries for pollution, people and planet?

Water and air are key to just about every process on planet Earth, from the physical to the biological. For humans, we need tens of liters of clean water a day, and unpolluted air to breathe that is free of health-threatening particulate matter. How do these basic needs for people and planet translate to guidelines and boundaries for pollution?

The Earth Commission’s Working Group on Nutrients and Pollution, or Working Group 3, is drilling into the science behind these issues, to devise safe targets for freshwater, air pollutants and the flow of nutrients and sediment to Earth’s many water bodies. The Working Group has selected its experts for inputs to start setting targets, in particular for nitrogen, phosphorus and atmospheric pollutants, and began its work earlier this year.

“We aim to identify targets for pollutants of inland waters — surface and groundwater — as well as for the major deltas of the world and coastal zone,” said Stuart Bunn, co-chair of the working group and professor at Griffith University (Brisbane, Australia), in a panel discussion on the Earth Commission held at last week’s Sustainability Research & Innovation Congress 2021 (SRI2021).

The group will ask a number of questions, including whether enough water is available to sustain freshwater ecosystems, as well as meet people’s needs for freshwater. “For most of these targets, we are taking a bottom up approach,” Bunn said, while noting a whole range of moderating processes that can affect the outcome for water availability.

Nitrogen and phosphorus, typically released to water bodies from farming, sewage, and industry, are naturally occurring elements that are key for both productive agriculture and thriving ecosystems. But human activities have markedly increased their presence in the environment, disrupting natural cycling processes and leading to eutrophication, algal blooms and anoxic “dead zones”.

To address nitrogen, the group is looking at surpluses and losses of nitrogen to determine a safe planetary level and impacts on the biosphere. Looking at nitrogen loads that are necessary for food production, Bunn noted, means that a ‘just’ level in terms of ‘access’ might need to be higher. “How much nitrogen will we need to feed a global population of 9 or 10 billion people by 2050? [This approach] will allow us to look across the globe to see where nitrogen should increase or decrease,” to meet a just target for food production but still remain safe, for people and planet, respectively.

Another aspect the group is considering is the transport of sediment from the land by rivers to the ocean. Increased sedimentation is projected from land use changes that lead to erosion and loss of vegetation, such as trees or grass alongside rivers that keep soil in place when water flows over the land surface. This increase is likely to be compounded by the projected increased frequency of extreme weather events with climate change, and accompanying increase in the amount of sediment that ends up in freshwater rivers and other bodies of water.

Meanwhile, dams also trap sediment, and an increased number of dams for water supply or for hydropower, the result of pushes for “green energy,” will further affect how much sediment reaches river deltas. Starved of sediment, river deltas will decline and become increasingly vulnerable to sea level rise. “The world’s large delta systems are a small area of Earth, but significant for human population and food production,” Bunn said at the SRI2021 meeting session on the Earth Commission. “What is the safe and just boundary of net sediment flux, taking into account sea level rise” and other conditions? — another focus for Working Group 3.

For atmospheric pollutants, the scientists will consider black carbon and nitrogen oxide gases, and possibly chlorofluorocarbons (CFCs). For example, particulate matter, which is related directly to climate change and the work of Working Group 1, impacts human health. Bunn noted that tropospheric ozone may also be important — to pollinators, as plants respond to shifts in sunlight. “Our work on atmospheric pollutants is still very much in development,” Bunn said, but setting targets or boundaries for atmospheric particulates, harm for human health with potential for impact to the Earth system will be important.

The results of the Working Group must navigate the tension between identifying a safe and just corridor for nutrients and pollution, for human harm and access. And those who are vulnerable may not be those who are creating the most impacts. “The guardrails on a highway may restrict the 1% from driving the way they want,” said Working Group 3 Co-Chair Chris Gordon of the University of Ghana (Legon, Accra), “but understanding where those boundaries are will save the lives of the rest of us who appreciate that living in a society means behaving in a commonly beneficial way.”