Planet Earth is on the edge. Secure the breached Earth system boundaries now

The Earth Commission recently released a report on ‘Safe and Just Earth System Boundaries’ authored by Johan Rockström and 50 other leading scientists from around the world. The report was published in the May issue of Nature.

The report notes that humanity is now in the Anthropocene Era, where human activities have been the dominant influence on climate and the environment. These activities have put the Earth system on a trajectory moving rapidly away from the stable Holocene state of the past 12,000 years. These rapid changes to the Earth system undermine critical life-support systems, with significant societal impacts already felt. They could lead to tipping points that irreversibly destabilise the Earth system.

These changes are mostly driven by socio-economic and other factors, such as unsustainable resource exploitation and consumption. The consequences of these impacts on the Earth system and human well-being vary significantly among social groups and countries.

Given these interdependencies between inclusive human development and a stable and resilient Earth system, the researchers assess the safe and just boundaries required to ensure the stability and resilience of the Earth system and human well-being in an integrated framework.

The researchers propose a set of safe and just Earth system boundaries (ESBs) for the climate, the biosphere, fresh water, nutrients, and air pollution at global and sub-global scales. These boundaries span the major components of the Earth system (atmosphere, hydrosphere, geosphere, biosphere, and cryosphere) and their interlinked processes (carbon, water, and nutrient cycles) that underpin the planet’s life-support systems and, thereby, human well-being. Human activities now threaten the stability of the Earth system and sustainable development.

To determine safe boundaries, the researchers use assessments of tipping point risks among local and regional tipping elements, evidence of declines in Earth system functions, analyses of historical variability, and expert judgement. Uncertainty and confidence levels are also accounted for in their analysis. Tipping elements are those components or processes that regulate the functioning and state of the planet and that show evidence of having thresholds at which small additional perturbations can trigger self-reinforcing changes that undermine Earth system resilience.

To assess where these ESBs protect people from significant harm, such as loss of lives and damages caused by extreme weather events, the researchers also incorporate justice considerations in their analysis. These considerations include interspecies justice and Earth system stability, inter- and intragenerational justice, and justice considerations across countries, communities, and individuals.

For global warming, the safe ESBs suggest that warming beyond 1.0°C above pre-industrial levels, which has already been exceeded (1.2°C), carries a moderate likelihood of breaching tipping elements and triggering collapse of the Greenland ice sheet or localised abrupt thawing of the boreal permafrost. Warming levels above 1.5°C or 2.0°C will lead to high or very high risks such as damaging the biosphere, converting global carbon sinks into carbon sources, and triggering other adverse consequences.

Stabilising at or below a safe ESB of 1.5°C warming, as agreed at the Paris Climate Summit in December 2015, avoids the most severe climate impacts on humans and other species. Even at 1.5°C without adaptation and compensation, about 200 million people, especially poor, marginalised, and vulnerable sections, will be exposed to the adverse effects of temperature rise, and 500 million people would be vulnerable to long-term sea-level rise.

For the biosphere, the safe ESBs consider two complementary measures of biodiversity: the area of largely intact natural ecosystems and the functional integrity of all ecosystems. Maintaining areas of largely intact natural ecosystems is necessary for securing the functions of the Earth system, on which all humans, other species, and Earth system stability depend. This includes stocks and flows of carbon, water, nutrients, and nature’s contributions to people. Based on climate, water, and species conservation model outcomes, the report suggests a safe ESB of 50–60% to maintain the functional integrity of ecosystems and their ability to provide ecosystem services. Currently, only one-third of human-dominated landscapes satisfy the ESB.

Loss of functional integrity in agricultural ecosystems and cities below the safe boundary would reduce food productivity, ecosystem capacity to mitigate natural hazards, pollution, and nutrient losses, and increase the reliance on harmful pesticides and biocides. 

With respect to water, the analysis considers two parameters: the flow alteration of surface water and the drawdown of groundwater. Flow alteration in rivers is a key driver of freshwater biodiversity loss and the decline of fisheries, on which millions depend for their livelihoods. Using a safe ESB of 80% unaltered surface water flow to ensure environmental and other needs, the report notes that annually only 66% of the global land area satisfies this ESB.

Groundwater extraction that exceeds replenishment rates will adversely impact groundwater-dependent activities and lead to land subsidence and irreversible aquifer loss. The study shows that in 47% of the basins, groundwater levels are declining, threatening the sustainability of groundwater-dependent ecosystems. If water quality issues are also considered, such as adhering to the standards for faecal coliforms and salinity content, the available water for human use and other needs will be lower.

Safe ESBs for other parameters such as nutrient cycling, air pollution, and other pollutants such as microplastics, radioactive wastes, heavy metals, and new emerging contaminants were analysed and show that the safe boundaries have been crossed. For example, according to the study, 85% of the world's population is currently exposed to air pollution caused by particulate matter concentrations beyond permissible levels, causing 4.2 million deaths annually, with vulnerable groups being affected the most.

Planet Earth is now on the edge, with seven of the eight globally quantified ESBs being breached, which imperils Earth system functioning, human wellbeing, and sustainable development. Will governments wake up from their deep slumber and take urgent concerted actions to pull the earth back from the precipice?

(The writer is Lead Author, GEO-7, UN Environment Programme, Kenya)