Planetary limits of land degradation
Healthy soils have a degree of resilience that allows them to maintain their structure and function in the face of repeated disturbances8.9including temperature disturbanceten, 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 earth, flood regulation and biodiversity conservation13. However, human-induced degradation, such as soil erosion, contamination and loss of organic carbon from the soil (Fig. 1), compromises the resilience of soils.3.14. 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 risk entering a downward spiral to an alternate 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 to sustain human life on Earth.14.16. As soil restoration is a slow process, soil is often viewed as a non-renewable resource6,9,14,15.
The downward spiral of land degradation is fueled by threats to soils that are strongly interrelated and linked by powerful feedback loops. At the local scale, loss of soil structure due to compaction by heavy machinery or intensive grazing results in loss of biota and soil functioning and further degradation.17. Globally, there is a strong positive feedback loop between soil erosion and climate change. Soil erosion causes loss of organic carbon from the soil in the form of carbon dioxide to the atmosphere, contributing to global warming14. Warmer conditions then lead to increased rainfall intensity, wind speed and forest fires, which can increase soil erosion.14.18.
Degraded soil condition is not uncommon in human history. The fall of past civilizations has been linked to the poor protection by societies of soil health19. Among these, the Sumerian civilization in Mesopotamia has been plagued by salinization and erosion of the highlands.19, while ancient Greece and the Roman Empire suffered from severe and widespread soil erosion19. Where healthy soils initially allow the growth and prosperity of civilizations, increased demand for food production and unsustainable agricultural practices lead to severe soil degradation. Followed by a decline in food security and political stability, land degradation compromises the resilience of civilizations and begins their collapse19. In the past, however, the human population was smaller, more dispersed, and less connected than today.6. This means that the past impacts of land degradation have only undermined local ecosystems and societies. Today, with a human population of 7.9 billion people expected to reach 9.8 billion by 2050 and a highly globalized world, land degradation is no longer a local problem.6. Land degradation is already negatively impacting the well-being of at least 3.2 billion people around the world20 decreasing food security and landscape resilience to extreme weather events, leading to increased inequalities and political instability15.20. In the European Union alone, the costs of soil degradation exceed 50 billion euros per year15. Globally, land degradation has also been linked to mass migration, violence and armed conflict.19.20. Land degradation is estimated to affect 90% of the world’s soils by 20503, which means that almost all of the world’s ecosystems and populations will be directly affected.