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According to scientists, four of the five environmental thresholds for a livable world have been exceeded. Illustrative image.
CLIMATE – Humanity is definitely exceeding its limits. A new study, published in the journal Nature on Wednesday, May 31, warns that “humans are taking enormous risks for their own future”. Authored by a scientific committee of 40 researchers from around the world, this study defines five quantified limits beyond which human life on Earth will no longer be “safe” or “just”.
If this work is new, it is the logical continuation of the publications by Swedish researcher Johan Rockstörm and his teams. As early as 2009, these scientists had identified nine planetary boundaries: turning points that have since become benchmarks in climate science. Today six of these nine planetary boundaries have been crossed.
Concretely, this means that human activities have destabilized the functioning of the planet to such an extent that it can never return to normal. In light of this observation, scientists wanted to compare the planet’s boundaries with those of humanity in a new study.
They have therefore identified five environmental variables for a “safe and just” world for humanity, making it possible to avoid rising mortality, climatic migration and, in places, the return of famine. These variables are climate, biosphere, water, nutrient cycles and air pollution. Their conclusion is alarming: four of these limit values have already been exceeded. Here you are.
1. The climate limit has been exceeded
It’s too hot and there’s no turning back. The planet has warmed by 1.2°C above pre-industrial levels due to greenhouse gas emissions. However, scientists assume in their work that for a safe planet, the warming should not be more than 1 °C.
The effects of climate change are already visible. “Emissions have already caused significant damage: extreme weather events, habitat loss by arctic indigenous communities, land loss by lowland states, sea level rise and reduced groundwater recharge,” the report said.
Should this climate limit be exceeded, there is still time to step on the brakes and try to limit the future consequences. Because when humanity reaches the 1.5°C warming mark, more than 200 million people, including the poorest, will face record temperatures, while more than 500 million will face sea-level rise.
2. The biosphere, limit crossed
Nature is disappearing at a rapid pace and this is already having an impact on people’s lives. In order to maintain a planet conducive to human life, at least 50 to 60% of the natural ecosystems on Earth would need to be preserved.
Humanity has already exceeded this quota. Only 45% of the natural ecosystems remain. The problem is that this destruction of nature leads to poorer water quality, an increase in pests and diseases, and negative consequences for people’s physical and mental health.
At the same time, agricultural land is becoming increasingly scarce. For mankind, this means less good harvests and an increasing dependence on pesticides. The report points to “unsustainable” practices such as deforestation or intensive farming.
3. Water, limit exceeded
In a safe world for humans, the natural course of the river is not changed by more than 20%. On Earth, 34% is currently disturbed by dams, drainage or other types of human intervention.
The same goes for groundwater: rainwater or snowmelt seeping into the ground and rocks, creating groundwater reserves. In theory, more groundwater should never be taken from it than is naturally replenished.
“Almost half of all land areas with river basins lie beyond this boundary,” the study estimates. This means that more water is withdrawn each year than is naturally renewed. “This over-abstraction endangers agricultural production and can lead to irreversible subsidence,” say the scientists.
4. Fertilizer limit exceeded
Fertilizers used in agriculture add unprecedented levels of nitrogen and phosphorus to the soil. While good yields can be achieved initially, the excess of these nutrients leads to ecosystem degradation in the long term. “This process is called eutrophication and can push aquatic and terrestrial ecosystems past a tipping point, beyond which biodiversity collapses,” explains researcher Johan Rockstörm.
While eutrophication threatens the survival of fish and other aquatic life, it also impacts human health. Since nitrogen and phosphorus occur naturally, they pollute the soil, but also the water. This is then the cause of the spread of toxic algae, such as the green algae in Brittany.
Excess nitrogen and phosphorus represent the fourth frontier that humanity is crossing. The maximum agricultural surpluses should be 61 TgN/year, while today they are 119 TgN/year. For phosphorus, the limit is between 4.5 and 9 teragrams of phosphorus per year, reaching 10 TgP/year in our world.
5. Air pollution, the only limit that is not exceeded
This is the only limit humanity has not yet crossed: air pollution, which scientists measure by the presence of aerosols. In their opinion, the limit will be exceeded on the day when there is too great an imbalance between the aerosol loads in the northern hemisphere and the southern hemisphere.
If that happens, there would be millions of premature deaths each year, a sharp rise in respiratory diseases, and irreversible changes in rainfall patterns. As air pollution levels continue to rise in the northern hemisphere, that scenario is drawing ever closer.
“Our planet and its inhabitants are threatened by air pollution. “We must act now to stop the increase in aerosol concentrations,” the researchers warn. The “good news” about air pollution must therefore be spread quickly, very quickly.
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