Humans have trespassed the planet's freshwater boundary, report says
Researchers found "evidence of widespread changes" in levels of soil moisture compared to pre-industrial conditions, meaning the planet has become drier since the Industrial Revolution.
They now believe the planet's freshwater boundary has already been "considerably transgressed", meaning that humans have affected the natural water cycle in a critical way that has made the planet less habitable.
The concept of "planetary boundaries" was created in 2009 as a model of the natural conditions necessary for humanity to operate safely.
Researchers monitor nine key dimensions of the Earth's systems, assessing the quantity, quality and state of resources in each sector. Each sector is limited by a boundary, which can be "transgressed" when resource use crosses a certain threshold.
Scientists made this realisation after reassessing the planetary boundary for freshwater to include "green water" - water moving through soil and plants. Previously, researchers only included "blue water" - rivers, lakes and groundwater - in their monitoring of this boundary.
“This is a wake-up call that we need to stop how we modify green water,” the lead author of the report Lan Wang-Erlandsson from the Stockholm Resilience Centre told US-based science outlet Mongabay.
Green water loss through soil drying can be caused by changes in soil use and agricultural practices.
"Green water" is depleting in all environments, but the findings are particularly worrisome for the Middle East, which is already battling water scarcity and "blue water" depletion. Abnormally dry soil is likely to become more common in the region due to climate change, which is expected to increase the frequency and intensity of drought episodes.
Water is one of the nine key boundaries used in this model, and the sixth to have been transgressed by humanity so far - and the second this year. In January 2022, humanity transgressed the boundary for novel entities, which includes plastic and manmade chemicals.