Seven of the nine thresholds that allow human life on Earth have already been crossed | Science

In 2009, a large group of scientists identified nine thresholds that humans must cross if Earth is to remain hospitable to civilization. Among others, there were fresh water availability, protected natural areas, pollution levels, the ozone layer and, of course, climate change. Now, a new report has been released Nature For the first time, it quantifies the thresholds for each of these problems to ensure that the Earth’s system is safe and fair not only for current humans, but also for future generations. Seven of them have already been breached in all or large parts of the planet. The apocalyptic picture is softened by the fact that the hole in the tropospheric ozone layer fell off the list: humanity managed to solve the problem in time.

A 2009 report identified limits to the Earth’s system, understood as a global ecosystem, that is sustainable and secure. It is written that if they are widely implemented, a series of catastrophic changes will follow. But since then, security has become associated with another idea: that the Earth system is not safe if it is not fair. One of the contributions of this new report is measurement justice between humans, other species and future generations.

“Humans are part of the Earth system. We are part of the problem and should be part of the solution,” summarizes Noelia Zafra, co-author of the work. “But problems and solutions do not affect everyone equally, and some humans bear the brunt of sustaining the Earth system while others benefit most. It also happens that a few create problems for many,” says this researcher from BC3, the Basque Center for Climate Change Research.

For example, this is the emissions that cause climate change. Its rise dates back to the beginning of the Industrial Revolution and its main protagonists are Europe and North America. Even now, half of greenhouse gas emissions come from the richest 10% of the population, with emerging countries like China beginning to shoulder a greater share of responsibility. “If we don’t all start from the same situation and there is conflict between us, we cannot work together to address the climate and biodiversity crisis”, Jafra adds.

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“It’s not a goal, it’s a limit”

The 2015 Paris Agreement set the goal of limiting climate change to 1.5º of global average warming. But that need for justice explains why the report’s authors further reduce the limit of additional warming the planet can support, reducing it to 1º. “1.5º is not a goal, it’s not a goal, it’s a physical limit,” Johann Rockström, director of the Postum Institute for Climate Change Research (Germany), recalled in an online press conference. From that threshold, the risks are very high, but even before it is exceeded, warming produces profound effects. Scientists say the temperature has already risen by an average of 1.2º and its impact can be felt on most of the planet and affect millions of people.

“Humans are part of the Earth system. We are a big part of the problem, and we have to be a big part of the solution.

Nolia Zafra, BC3 researcher

One of the contributions of this report is that it does not stop with the climate emergency. For its authors, it is already clear that climate change is not the only existential problem facing human civilization. Another of the scaled thresholds relates to the part of the planet that still preserves its original state. Work promoted by Land CommissionA coalition of leading scientists to keep 50% to 60% of the land free from livestock, agriculture, mining or any other human interference. “Currently, we are at 45% to 50%. So, below the threshold”, recalls David Obura, co-author of the CORDIO organization and study. Obura also points out that the planet’s eroded regions can still add resilience to the Earth system. Millions of hectares dedicated to pastures and crops – even cities – could be part of the solution, as for every square kilometer of the environment, at least 20% should be vegetation, even if it’s not natural.

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Other limits that have been measured and already exceeded are the additional nutrients that humans contribute to the Earth. Specifically, they measure anthropogenic nitrogen and phosphorus used primarily in agriculture. An excess of these elements changes both the substrate and the water in a process called eutrophication. Cases such as Mar Manor in Murcia illustrate this well. Limits have not yet been exceeded globally, but large areas of the planet must use water, both surface and underground. According to the report, one-third of the planet is already over-extracted from surface water resources, with the limit set at 20%. In the case of groundwater, the rate of recharge in half of the Earth is not respected. As for air pollution caused by the emission of particles of non-natural origin (mechanical combustion, heating and cooling, industrial emissions…), the limit has not yet been exceeded globally, but it has already been exceeded in various categories. Parts of the planet like Southeast Asia.

“Contaminants such as fresh water, air, nitrogen and phosphorus, the integrity of the biosphere provides resilience and stability to the entire Earth system”

Johann Rockström, director of Germany’s Postum Institute for Climate Change Research

The report acknowledges that this leaves problems such as ocean acidification, plastic and microplastic accumulation, persistent chemicals or antibiotics. They consider threats that have not yet been sufficiently studied to determine whether they pose existential risks. A number of other problems are also associated, such as accelerated biodiversity loss due to excess nutrients. Others, like climate change, exacerbate others.

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“If we study pollutants like fresh water, air, nitrogen and phosphorus, or the integrity of the biosphere in terms of surface and biodiversity, we do it with purpose, because when they add up, they provide resilience, buffering capacity. Stability for the whole Earth system,” Rockstrom said at the press conference. Exceeding each threshold in these areas reduces “the planet’s resilience to the climate crisis.” And he adds: “Seven of the eight indicators we assessed are outside the fair and safe space. We also see that there is a window so that change that restores that safe space is still possible. But it needs changes and very, very fast action. Simply decarbonizing the global energy system will not be enough.

How to do it? From BC3, Jafra recalls the challenge involved: “There can be no human well-being without the Earth system. Reconciling the well-being of all humans with the limits of the Earth system, what well-being really means, how good we want it to feel, and how willing we are to harm other people and creatures. It involves asking ourselves to undertake broader social processes at all scales that allow for inclusive and just changes to tackle the climate and biodiversity crisis.

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