Earth past its safe limits for humans, scientists say

The earth is already past safe limits for humans as temperature rise, water system disruption and destruction of natural habitats have reached boundaries, a study by a group of the world’s foremost scientists has found.

The research, published in the journal Nature on Wednesday, identified eight earth system boundaries that included climate, biodiversity, water, natural ecosystems, land use and the effect of fertilisers and aerosols.

Human activities had pushed seven of these boundaries beyond their “safe and just limit” into risk zones that indicate the threat to planetary and human health, it said.

Researchers have traditionally focused on the effects of climate change or biodiversity loss on the planet itself, but the study from the Earth Commission group of scientists marks an attempt by experts to identify the limits after which humans will suffer significant harm.

That includes through a lack of access to clean water, lower food security and displacement or loss of work because of temperature rise or flooding.

Johan Rockström, director of the Potsdam Institute for Climate Impact Research and co-author of the report, said it was “very worrying” that most of the boundaries had already been breached.

“It’s starting to hurt already . . . causing extreme events and abrupt impacts which go beyond heatwaves, droughts and floods caused by climate [change], but also lower food security, worsening water quality, overdraft of groundwater [and] worsened conditions for livelihoods, particularly among the vast vulnerable majorities in the world,” he said.

“It’s not only climate causing risks of displacement, migration and potentially conflicts, it’s the totality of these breaching these safe and just boundaries.”

According to the research, the “safe and just” limit, which takes into account the impact on planet and people, for global temperature rise is 1C higher than pre-industrial times.

But this increase is already at least at 1.1C, or as much as 1.2C, according to the study. Under the Paris agreement, world governments pledged to limit the rise to 2C and ideally 1.5C, the level at which irreversible planetary changes are expected to take place.

The Earth Commission researchers said that at a rise of 1.5C, more than 200mn people would be exposed to unprecedented mean annual temperatures and more than 500mn could be exposed to long-term sea level rises.

Between 50 and 60 per cent of the earth needed to be covered by largely intact ecosystems — a level that had already been breached, the study said.

The use of nitrogen as a fertiliser needed to halve, it also concluded, to reduce the excessive growth of plant and algal blooms on surface water, and to lower ammonia and nitrogen oxide emissions.

The so-called Earth system is made up of many interdependent processes that keep the planet stable, but when disrupted alter its habitability.

Rockström said all of the various earth systems boundaries outlined in the research were “interconnected”, meaning that overshooting the safe limit for one could have a knock-on impact on others.

“If you want to solve the climate crisis, you need the other boundaries intact as well. When you have a climate crisis, you want a healthy planet . . . but we have a weaker planet than ever before,” he said.

The researchers used the same units of measurement to incorporate “justice” for people into scientific analysis as was used for the safe limits for the planet.

Xuemei Bai, an Australian National University professor and co-author, said that in “putting a number on human needs and impacts”, the study “shows how the protection of the planet is inseparable from the success of communities, societies and economies”.

Research from the Intergovernmental Panel on Climate Change this year found that the richest 1 per cent of the world’s population was responsible for twice the carbon dioxide emissions of the poorest 50 per cent.

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