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

In 2009, a large group of scientists identified nine limits that humans should not cross if they want Earth to remain hospitable to civilization. There were, among others, the available fresh water, the natural area that is conserved, the pollution levels, the ozone layer and, of course, climate change. Now, a new report just published in Nature For the first time, it quantifies the thresholds for each of these problems that should not be exceeded in order for the Earth system to be safe and fair not only for current humans, but for future generations. Seven of them have already been exceeded in all or in large areas of the planet. The apocalyptic picture is softened by the fact that the hole in the tropospheric ozone layer has fallen from the list: humanity was able to solve the problem in time.

The 2009 report identified those limits for the Earth system, understood as a global ecosystem, to be sustainable and secure. It was then written that, if they were widely passed, a series of catastrophic changes would follow. But since then, security has been joined by another idea: the Earth system will not be secure if it is not also fair. One of the contributions of this new report is the quantification of the justice between humans, the rest of living beings and future generations.

“Human beings are part of the Earth system. We are a large part of the problem and we have to be a large part of the solution”, summarizes Noelia Zafra, co-author of the work. “But the problems and the solutions do not affect everyone equally, and there are some human beings who bear the inconvenience of sustaining the Earth system, while others mostly benefit. It also happens that a few create problems for many”, adds this researcher from BC3, the Basque center for climate change research.

This is the case, for example, of the emissions that are causing climate change. Its increase dates back to the beginning of the Industrial Revolution and its main protagonists, Europe and North America, are responsible for it. Even now, as emerging countries like China are beginning to take on a large share of responsibility, half of greenhouse gas emissions come from the richest 10% of the population. “We will not be able to act together to face the climate and biodiversity crisis if we do not all start from the same situation and there is conflict between us”, adds Zafra.

“It is not a goal, it is a limit”

The 2015 Paris Agreement set the acceptable increase in global average temperature at 1.5º to curb climate change. But that need for justice explains why the authors of the report further reduce the limit of the extra warming that the planet could support, lowering it to 1º. The director of the Postdam Institute for Climate Change Research (Germany), Johan Rockström, recalled in an online press conference that “1.5º is not an objective, it is not a goal, it is a physical limit.” From that limit, the risks are very high, but even before exceeding it, warming is generating profound consequences. Scientists estimate that the temperature has already risen by an average of 1.2º and the impact can be felt in most of the planet and suffered by millions of people.

“Human beings 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”

Noelia Zafra, BC3 researcher

One of the contributions of this report is that it does not stop at the climate emergency. For its authors, it is already evident that climate change is not the only existential problem facing human civilization. Another of the quantified thresholds is the one that has to do with the portion of the planet that still preserves its original state. The work promoted by Land Commission, an alliance made up of leading scientists, set between 50% and 60% of the land surface to be kept free of livestock, agriculture, mining or any other human interference. “Currently, we are between 45% and 50%. So, just below the limit”, recalls David Obura, from the CORDIO organization, and co-author of the study. Obura also points out that denatured areas of the planet can still add resilience to the Earth system. The millions of hectares devoted to grazing and crops – even cities – can be part of the solution, provided that for every square kilometer of ecosystem altered, a minimum of 20% should have vegetation, even if it is not natural.

Other of the thresholds quantified and already exceeded are the extra nutrients contributed by humans to the earth. In particular, they quantify anthropogenic nitrogen and phosphorus used primarily in agriculture. An excess of these elements alters both the substrate and the water in a process known as eutrophication. Cases such as the Mar Menor in Murcia illustrate this very well. The limits not yet exceeded globally, but in large areas of the planet, have to do with the use of water, both surface and underground. According to the report, in a third of the planet there is already an excess extraction of surface water resources, the limit of which has been set at 20%. For groundwater, the replenishment rate is not respected in half the Earth. Regarding air pollution caused by the emission of particles of non-natural origin (engine combustion, heating and cooling, industrial emissions…), the limit is still far from being exceeded on a global scale, but it has already been exceeded in various regions of the planet, such as Southeast Asia.

“Fresh water, air, pollutants such as nitrogen and phosphorous, the integrity of the biosphere provide resilience and stability to the entire Earth system”

Johan Rockström, Director of the Postdam Institute for Climate Change Research, Germany

The report acknowledges that it leaves out problems such as ocean acidification, the accumulation of plastic and microplastics, persistent chemicals or antibiotics. They maintain that they are threats that have not yet been sufficiently studied to determine if they pose existential risks. Several of the problems are also related, such as the loss of biodiversity accelerated by excess nutrients. And others, like climate change, amplify the severity of the others.

“If we study fresh water, air, pollutants such as nitrogen and phosphorous, or the integrity of the biosphere both in terms of surface area and biodiversity, we do it that way on purpose because if they add up, they provide resilience, buffering capacity and stability to the entire Earth system,” Rockström said at the press conference. Exceeding each threshold in these areas reduces “the strength of the planet to face the climate crisis.” And he adds: “Seven of the eight indicators that we have been evaluating are outside of the fair and safe space. We also see that there is a window so that a transformation that recovers that safe space is still possible. But it requires transformations and very, very fast action. And it will not be enough to simply decarbonise the global energy system.”

How to do it? From BC3, Zafra recalls the challenge he poses: “Human well-being cannot exist without the Earth system. Reconciling the well-being of all human beings fairly with the limits of the Earth system involves asking ourselves what well-being really is, what and how much we need to feel good, how much we are willing to harm other people and living beings to achieve what, and carry out broad social processes at all scales that allow for inclusive and just transformations to tackle the climate and biodiversity crisis.”

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