Climate change, land use, air pollution: we humans shape the shape and future of our planet. A study is now defining threshold values within which we are unlikely to seriously upset natural systems – and at the same time prevent millions of people from suffering serious damage. Unlike previous approaches, which mainly relied on biophysical factors, the study also includes sociopolitical factors. This leads to significantly stricter limit values in some areas. Many of these have already been exceeded.
We humans shape our environment so much that scientists classify our age as a new geological epoch: the Anthropocene. Due to human influences, our world is rapidly moving away from the stable state of the previous age, the Holocene. The climate is warming faster than in the millennia before, biodiversity is falling and air pollution is increasing. As early as 2009, researchers defined nine so-called planetary boundaries, which are intended to define safe room for mankind to act. These limit values – including for global warming, water use and the stability of ecosystems – have been revised several times since then. So far, however, they have been based primarily on global considerations of biophysical control systems.
"Safe" and "fair" limit values
“We are presenting, for the first time, quantifiable numbers and a solid scientific basis to assess the state of our planetary health not only in terms of Earth system stability and resilience, but also in terms of human well-being and equity,” says Johan Rockström from the Potsdam Institute for Climate Impact Research. Together with an international research team, he has defined limit values in eight areas on the basis of previous studies and his own models: the climate, the natural ecosystem area, the functional integrity of the ecosystems, surface water, groundwater, nitrogen, phosphorus and aerosols.
The team distinguishes between safe and fair limit values. Consistent with the previously defined planetary boundaries, the "safe" limits refer to maintaining or restoring the stability of the Earth system. In the area of climate, for example, limiting global warming to 1.5 degrees Celsius is considered safe, since below this value numerous climatic tipping points can be avoided. But even below this "safe" limit, millions of people suffer from climate-related damage: They are exposed to extremely high temperatures, suffer from water and food shortages or have to fear that their homes will soon become uninhabitable.
impact on people
The “just” limit values therefore aim to protect people from significant damage. "Justice is a necessity for humanity to live within planetary boundaries," says co-author Joyeeta Gupta from the University of Amsterdam. “The overwhelming evidence shows that a just and equitable approach is essential to planetary stability. Without justice we cannot have a biophysically safe planet. This includes setting just goals to prevent significant harm and guaranteeing people access to resources, and just changes to achieve those goals.”
This leads to significantly stricter limits. With regard to global warming, for example, the team concludes that the temperature increase compared to the pre-industrial age should be limited to one degree Celsius. This value has already been exceeded with 1.2 degrees of current warming. We are also currently not complying with the other fair limit values that have been set. We use more groundwater than can regenerate, release more nitrogen and phosphorus into nature through fertilizers than ecosystems can tolerate, and pollute the air, at least in some regions, to such an extent that the people living there have to fear serious damage to their health.
solutions are still pending
“Our secure and just borders serve as a guide for setting goals, but must also be implemented through just transformation processes that ensure people have a minimum level of access to resources,” says Gupta. According to the research team, justice includes both justice between people living today in different regions of the world, justice towards future generations and justice towards our non-human fellow creatures.
The team of authors has not worked out what exactly just transformation processes could look like. "Many questions about the interaction of human development and livelihoods ultimately remain unanswered," comments Gregor Hagedorn from the Leibniz Institute for Evolutionary and Biodiversity Research in Berlin, who was not involved in the study. “How methodologically sound is the inclusion of aspects of justice and their quantification? As long as the social development goals are only briefly addressed, but not quantified, the resulting minimum burden on the basis of life for a just world cannot be quantified. Further work will probably follow here.”
In an accompanying commentary on the study, also published in the journal Nature, Stephen Humphreys of the London School of Economics and Political Science writes: "While the work raises more questions than it answers, it is a crucial step in bridging the gap between biophysical and sociopolitical research. It is hoped that it will bring us closer to realizing a truly safe and just Earth system.”
Source: Johan Rockström (Potsdam Institute for Climate Impact Research, Potsdam) et al., Nature, doi: 10.1038/s41586-023-06083-8