Thomas Krautwig, Anja Krieger

How we observe planetary boundaries

Our planet has capacity limits for air pollution, biodiversity, the extent of climate change, and other factors. These are boundaries that must be respected if we are to preserve the basis for human life. The concept of planetary boundaries defines these guardrails. It comprises nine categories that are crucial to the health and viability of human civilization. We have already overstepped some of these boundaries. How can we return to the safe zone?

The nine planetary boundaries according to Rockström, Stockholm Resilience Center
The nine planetary boundaries according to Rockström, Stockholm Resilience Center
Illustration: Planetary Boundaries
©
Julia Blenn / Helmholtz-Klima-Initiative

Our modern societies have developed over the past 10,000 years in a relatively stable state of the Earth system during the Holocene epoch. But in recent decades, we have changed the conditions on our planet dramatically. Our greenhouse gas emissions are driving climate change and causing ocean acidification. Our fields, roads, and houses change the landscape, our vehicles and factories pollute the air. Some of the new chemicals we are releasing into the environment have a health impact on humans and ecosystems. We affect the hydrological balance, change important cycles, and are responsible for the extinction of many species.

Johan Rockström, a scientist at the Stockholm Resilience Center, found our interventions in natural systems are chipping away at the parameters required to sustain our own future. In 2009 he developed the planetary boundaries concept, which has since been modified several times. Below, on the occasion of Earth Overshoot Day, we show in a nine-part series which planetary boundaries have already been exceeded and which have not, how scientists determine this, and what we can do to ensure a safe future.

The illustration shows which boundaries we have exceeded and by how much. Click on the graphic to enlarge it. The green circle in the center symbolizes our safe operating space. The orange zones outside the center show where planetary boundaries have already been crossed and by how much. The situation in the gray zones is still unclear and requires more scientific research. Find the short version as well as the links to our in-depth articles on all nine planetary boundaries here:

Humanity has released numerous substances into the environment that were not there before: plastics, dyes, fire retardants, etc. Since they were rarely or never involved in evolutionary processes, organisms have not been able to develop strategies to cope with these xenobiotics. In 2022, researchers determined that the planetary boundary for novel entities has already been exceeded for chemicals and plastics. Read more >

Biodiversity and intact ecosystems are important stabilizing factors for the entire Earth system. However, human intervention in natural systems is threatening this ecological stability. Global diversity loss has accelerated such that we have already crossed this planetary boundary. The size of populations, as well as the number of organisms and their distribution, are also important for assessing future risks – but more data is still required. Read more >

Life could not exist without nitrogen and phosphorus. Like other important nutrients, these chemical elements circulate in cycles and quantities that ecosystems have adjusted to over the course of evolution. But humans have caused serious imbalances in these cycles. There is too much nitrogen and phosphorus in circulation. At the same time, there is a growing shortage of phosphorus. This boundary has been exceeded by a wide margin. Read more >

The availability of freshwater and moist, temperate air is crucially important for humans, plants, and many other life forms. Until now, researchers assumed that we had not yet exceeded the planetary boundary for the Earth’s hydrological balance. But now it appears that the “green water” is falling to ever-lower levels, particularly the water available to plants from rain, soil moisture, and evaporation. This component is already in the risk zone. This is in contrast to the situation with rivers, lakes, and groundwater, which is less concerning for now. Read more >

Agriculture and settlements are changing the landscape. There has been a major conversion of forests into farmland in the past 50 years. Large forested regions have lost important ecosystem functions. This planetary boundary has already been exceeded, although its measurements are not as far into the red zone as some others. Read more >

Climate change is accelerating. Global warming is also becoming noticeable in Germany. Heat waves, floods, and droughts are only a few of the consequences. The risk of abrupt and irreversible changes to the Earth system rises with every tenth of a degree Celsius of temperature increase. This planetary boundary has been exceeded. Read more >

Human emissions of particles (aerosols) such as soot into the atmosphere are not just bad for our own health. They also lead to changes in the climate system. We are not yet certain whether the planetary boundary for atmospheric aerosols has already been exceeded or if we are still in the safe zone; more scientific research is needed. However, adverse effects can already be observed at the regional level. Read more >

The oceans are becoming more and more acidic; their pH value is decreasing. This is because there is more and more carbon dioxide in the atmosphere, and it dissolves in the ocean’s water. Since marine organisms have shells and skeletons made of lime, it is more difficult for them to grow and survive in the more acidic water. Another result is that the oceans produce less oxygen and store less carbon dioxide, and the food supply for other marine animals decreases. The planetary boundary for acidification has not been exceeded yet.

The stratospheric ozone layer protects all life from hazardous ultraviolet radiation. In 1985, scientists noticed that this protective shield had become thinner over the Antarctic. The cause of the “ozone hole” was chlorofluorocarbons (CFCs), a group of chemicals that can also be harmful to the climate. The international community acted quickly and phased them out. Today the ozone layer is gradually recovering. Bold policies ensured that this planetary boundary was not exceeded. Read more >

The goal of establishing planetary boundaries is to act according to the precautionary principle, which states that environmental stresses that can also be harmful to human health should be avoided. In this way, potential risks can be avoided even when knowledge is incomplete. In other words, this is a way to avoid damage to the environment since our current state of knowledge does not allow us to assess impacts and interactions outside the safe parameters.

Six of the nine planetary boundaries have now been exceeded. For example, we have warmed the atmosphere by 1.2°C globally and are on our way to overstepping a variety of irreversible tipping points in the climate system.

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