Planetary limits to soil degradation

Healthy soils have a degree of resilience that allows them to maintain structure and function in the face of repeated disturbance8,9, including temperature perturbation10, compaction11 and copper pollution12. They provide essential ecosystem services3 such as food production and can help us achieve several Sustainable Development Goals, including zero hunger, clean water and sanitation, life on land, flood regulation, and conservation of biodiversity13. However, human-induced degradation, such as soil erosion, contamination, and loss of soil organic carbon (Fig. 1), is compromising soil resilience3,14. Population growth, unsustainable agricultural practices, deforestation, industrial development, urbanization, and increasingly climate change pose the greatest threats to healthy soils3,14,15. Once disturbed beyond a critical level, soils are at risk of entering a downward spiral towards an alternative, degraded state9,14. This degraded state is characterized by a loss of soil functions and services including the ability to provide food for humanity and sustain human life on Earth14,16. As soil restoration is a slow process, soil is often considered a non-renewable resource6,9,14,15.

Fig. 1: Soil degradation.

The process of soil degradation depicted by the main drivers, quantifiable threats and the consequences of soil degradation on planetary and societal health.

The downward spiral of soil degradation is fueled by soil threats that are strongly interrelated and linked through powerful feedback loops. On a local scale, loss of soil structure due to compaction by heavy machinery or intensive grazing results in loss of soil biota and soil functioning and further degradation17. On a global scale, there is a strong positive feedback loop between soil erosion and climate change. Soil erosion causes a loss of soil organic carbon as carbon dioxide to the atmosphere, contributing to global warming14. Warmer conditions then drive increases in rainfall intensity, wind speed, and wildfire, all of which can increase soil erosion14,18.

A degraded soil state is not uncommon in human history. The fall of past civilizations has been linked to societies’ poor protection of soil health19. Among these, the Sumerian civilization in Mesopotamia was undermined by salinization and upland erosion19, while both Ancient Greece and the Roman Empire suffered from widespread, severe soil erosion19. Where healthy soils initially enable the growth and prosperity of civilizations, the increased demand for food production and unsustainable agricultural practices result in severe soil degradation. Followed by a decrease in food security and political stability, soil degradation compromises the resilience of civilizations and initiates their collapse19. In the past, however, the human population was smaller, more scattered, and less connected than at present6. This means that past impacts of soil degradation only undermined local ecosystems and societies. Today, with a human population of 7.9 billion people that is expected to grow to 9.8 billion by 2050 and a strongly globalized world, soil degradation is no longer a local issue6. Land degradation is already negatively impacting the wellbeing of at least 3.2 billion people worldwide20 by decreasing food security and resilience of the landscape to extreme weather events, resulting in an increase in inequality and political instability15,20. In the European Union alone, costs related to soil degradation exceed 50 billion euro’s a year15. On a global scale, soil degradation has also been linked to mass migrations, violence, and armed conflict19,20. Soil degradation is estimated to affect 90% of the soils globally by 20503, meaning almost all global ecosystems and populations will be directly affected.

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