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Setting boundaries for a safe Earth requires a consideration of justice, scientists say

Global actors must adhere to both boundaries for a safe and just Earth to maintain a planet that can truly sustain life, scientists say.

(CN) — A biophysically safe planet cannot exist without justice and equity, scientists say in a new study in the journal Nature that assesses, for the first time, safe and just boundaries for the climate, biodiversity, freshwater and pollution.

The Paris Agreement set a goal of limiting global warming to a temperature increase of no more than 1.5 degrees Celsius above pre-industrial levels, but scientists with the Earth Commission — a global team of natural and social scientists — say the world has already passed what they call the "safe and just climate boundary" of 1 degree Celsius above pre-industrial levels. Moreover, these scientists say there is also an urgent need to manage a wide array of biophysical systems and processes that determine Earth's habitability beyond climate change.

Human activities have altered the flow of water, released excessive amounts of nutrients into waterways from fertilizer use, and reduced the number of natural areas.

"The results of our health check are quite concerning: Within the five analyzed domains, several boundaries, on a global and local scale, are already transgressed,” said Johan Rockström, Earth Commission co-chair and lead author of the study. “This means that unless a timely transformation occurs, it is most likely that irreversible tipping points and widespread impacts on human well-being will be unavoidable. Avoiding that scenario is crucial if we want to secure a safe and just future for current and future generations.”

A just planet necessarily means there's less available space for humans on it, but justice is necessary for habitability, the study's authors said. That's why they considered how to avoid significant harm to humans and other species as they defined earth system boundaries that built upon what scientists know are the biophysical conditions to maintain a livable, stable planet.

“The new research provides safe and just earth system boundaries for five critical domains that play a key role in life support and Earth stability," said lead author Steven Lade, a research scientist at the Australian National University and Stockholm Resilience Center and Earth Commission Secretariat. "It also explores what’s needed to minimize significant harm to humans as a result of changes in the Earth system and sets boundaries at scales relevant for assessment and management of the conditions of biophysical systems such as the biosphere and freshwater."

The scientists say, for example, that an Earth system boundary that is both safe and just pertaining to ecosystem area — which is affected by loss of climate, water, biodiversity and nature's contribution to people — must combine the safe boundary of maintaining at least 50-60% of Earth's land surface covered by intact natural areas with the consideration of distributional justice.

"Adherence to our proposed safe [Earth system boundary] for the area of largely intact natural ecosystems should minimize harm to future generations ... by securing biosphere contributions to all life support through a stable and resilient Earth system and localized [nature's contribution to people] provided by largely intact nature," the study states.

"However, achieving justice for current generations ... may require a stricter boundary because the safe [Earth system boundary] does not account for the current uneven distribution of largely intact natural ecosystems needed to support local livelihoods, especially in poor or Indigenous communities," the study adds. "Some people and countries may directly benefit from policies to maintain or increase natural ecosystem area, while others may face opportunity costs."

When considering boundaries for fresh water flow alteration in rivers, which the study says is one of the primary causes of freshwater biodiversity loss, and groundwater levels, the scientists said that minimizing harm to current generations requires a consideration of water insecurity in various parts of the world and "addressing surface water quality guidelines for human use, not just an allocation of water quantity," among other factors.

Aerosol pollution was one of the two cases, along with climate, that the study notes resulted in more stringent just boundaries than safe boundaries. Eighty-five percent of people on Earth are currently exposed to particulate matter concentrations of more than 15 micrograms per cubic meter on average annually, which is the boundary the scientists set to avoid a high likelihood of significant harm.

"Aerosols are associated with respiratory illnesses and premature deaths as well as heart problems and debilitating asthma," the study states.

The study noted that many of safe and just Earth systems boundaries have already been crossed.

“A safe and just transformation to a manageable planet, requires urgent, collective action by multiple actors, especially in government and business to act within Earth system boundaries to keep our life support system of the planet intact. Stewardship of the global commons has never been more urgent or important,” Earth Commission Executive Director Wendy Broadgate said.

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