A reassessment of the planet’s freshwater boundary indicates it has already been breached, according to an international team of researchers led by the Stockholm Resilience Center and including the Potsdam Climate Impact Research Institute. This conclusion is due to the consideration for the first time of “green water” – the water available to plants – in the assessment of the limits.
“Water is the blood of the biosphere. But we are profoundly modifying the water cycle. This affects the health of the entire planet, making it significantly less resilient to disturbances.says lead author Lan Wang-Erlandsson of the Stockholm Resilience Center (SRC) at Stockholm University.
The planetary boundaries framework was first published in 2009 under the direction of Johan Rockström, then director of the SRC, now director of the Potsdam Institute and co-author of the new study. Planetary boundaries define the safe operating space for humanity. Water is one of nine regulators of the state of the Earth system, and it is the sixth boundary that scientists have assessed as being violated. Other transgressed boundaries are: climate change, biosphere integrity, biogeochemical cycles, land use change and, in 2022, new entities, which include plastic and other chemicals from human origin.
Distinction between “blue water” and “green water”
Until now, the water limit was considered to be inside the safety zone. However, the original limit on fresh water only related to the extraction of water from rivers, lakes and groundwater, known as “blue water”.
Now researchers have studied the water boundary in more detail. The authors argue that previous assessments do not sufficiently capture the role of green water, and in particular soil moisture, in ensuring biosphere resilience, securing terrestrial carbon sinks, and regulating atmospheric circulation.
“The Amazon rainforest depends on soil moisture for its survival. But there is evidence that parts of the Amazon are drying up. The rainforest is losing soil moisture due to climate change and deforestationsays Arne Tobian, second author and PhD student at the Stockholm Resilience Center and the Potsdam Climate Impact Research Institute. “These changes potentially bring the Amazon closer to a tipping point where large parts could shift from jungle to savannah-like states.” Add.
And it’s not just in the Amazon. This phenomenon is global. Everywhere, from boreal forests to the tropics, from farmland to woods, soil moisture is changing. Abnormally wet and dry soils are increasingly common.
“This latest scientific analysis shows how we humans could push green water far above the variability that Earth experienced for several thousand years in the Holocene period.concludes Rockström. “This is serious and poses a threat to life support systems on Earth, caused by global warming, unsustainable land management and the destruction of nature.“.