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By Roger Highfield on

Earth heading beyond its safe limits for humans

Roger Highfield, Science Director, reports on a study that finds human activities have transgressed 7 out of 8 ‘planetary boundaries’.

Earth is breaching its safe limits for humans, according to a study by an international group of scientists, the Earth Commission.

The study was published last week in the journal Nature as atmospheric carbon dioxide measured at NOAA’s Mauna Loa Atmospheric Baseline Observatory peaked at 424 parts per million in May, continuing a steady climb further to levels not seen for millions of years.

Original air-sampling flask used by Charles David Keeling for observations of atmospheric carbon dioxide
Original air-sampling flask used by Charles David Keeling for observations of atmospheric carbon dioxide © Science Museum Group

The Earth Commission team has developed the idea of ‘planetary boundaries’, first set out in an influential 2009 paper that defined a set of interlinked thresholds that it said would ensure a ‘safe operating space for humanity’, in which it rejected ‘human exceptionalism’ by focusing on all species and ecosystems.

The study was carried out by Johan Rockstrӧm, Steven Lade and a team of around 40 scientists to quantify planetary boundaries involving climate, the biosphere, freshwater, nutrients, and air pollution beyond which the planet would tip into an irreversible state.

Among the co-authors is Tim Lenton of the Global Systems Institute, University of Exeter, who pioneered research on these ‘tipping points‘, abrupt shifts in the state of parts of the global climate system, with potential impacts that cannot be reversed. ‘Taking an integrated view of what is safe for the Earth system and what is just for the people within it gives us the clearest view yet of the transformational changes we need to make in our societies to stay within Earth system boundaries,’ he said.

The Earth Commission quantified safe and just boundaries for climate, air pollution, phosphorus and nitrogen contamination of water from the overuse of fertiliser, groundwater supplies, fresh surface water, the unbuilt natural environment and the overall natural and human-built environment.

While the ‘safe boundaries’ identified by the study maintain and enhance the Earth system’s stability and resilience, the ‘just boundaries’ are the limits that protect people from significant harm.

Most of these boundaries have been breached, however. ‘Within the five analysed domains, several boundaries, on a global and local scale, are already transgressed,’ said Johan Rockström, Earth Commission Co-Chair, lead author and Director of the Potsdam Institute for Climate Impact Research. ‘Unless a timely transformation occurs, it is most likely that irreversible tipping points and widespread impacts on human well-being will be unavoidable.’

Only air pollution had not quite reached the danger point globally. ‘We are in a danger zone for most of the Earth system boundaries,’ said study co-author Kristie Ebi, a professor of climate and public health at the University of Washington.

This approach underlines the challenges facing humanity of what some call the Anthropocene, a proposed geological epoch where human pressures have put the Earth system on a rapid trajectory away from the stable Holocene state of the past 12,000 years that has supported life as we know it.

The Paris climate agreement aims to limit warming to 1.5° C above preindustrial levels to avoid the most severe impacts but, the authors say, that does not avoid significant harm to millions of people – such as loss of lives, displacement, loss of food or water security – and they propose the safe and just climate boundary should be set at or below 1.0° C.

But the world has already passed the safe and just climate boundary, which is set at 1°C above pre industrial temperature levels, as tens of millions of people are already harmed by the current level of climate change.

Diagram showing Safe and Just Earth System Boundaries
Safe and Just Earth System Boundaries diagram. Credit: Earth Commission.

‘The Earth is really quite sick right now and it is sick in terms of many different areas or systems and this sickness is also affecting the people living on Earth,’ said co-author Joyeeta Gupta, Co-Chair of the Earth Commission. ‘By setting our climate Earth System Boundary at 1°C we are not advocating that the world should adopt this ambitious target, but we are exposing the injustice inherent in current world targets.’

The Earth Systems Boundaries will underpin new science-based targets for businesses, cities and governments. ‘Stewardship of the global commons has never been more urgent or important,’ continued Wendy Broadgate, Earth Commission Executive Director.

On Sunday 11 June 2023, Roger Highfield will discuss The Case for Nature at the Jaipur Literature Festival, British Library, London, with authors Siddarth Shrikanth and Gaia Vince.