Our planet is relatively massive, but it is a world of finite resources and we are quickly approaching our limits. The planetary boundaries framework establishes how safely humanity can operate within Earth's biological and physical limitations before undermining our own ability to survive. This is why when burning fossil fuels causes global heating, scientists warn about the safe upper limits of climate change.
Yet climate change is just one of the nine planetary boundaries that humanity must respect for Earth to remain a healthy planet for our species. Unfortunately, according to a recent study in the journal Science Advances, humanity is not merely failing to respect the climate boundary — we're at existential risk for six of the nine planetary boundaries that exist.
"The planetary boundaries framework, introduced in 2009, identifies guardrails for humanity's impacts on the global environment," explained the study's lead author Dr. Katherine Richardson, professor in Biological Oceanography at the University of Copenhagen's Sustainability Science Centre, in an email to Salon. "Current scientific understanding suggests respecting these guardrails would minimize the risk of human activities triggering a dramatic and potentially irreversible change in global environmental conditions."
Those "irreversible changes" could result in widespread suffering, from famine to pandemics to outbreaks of war. Although human beings need Earth's resources to survive, if they overuse those resources, they will eventually find that the planet is no longer hospitable for them.
"We can think of the Earth's resources as the currency that supports us," Richardson told Salon. "The planetary boundaries framework is like a bank statement — it tells us how much of various components (resources) of the Earth system we can allow ourselves to us without greatly increasing the risk that our activities will lead to dramatic and potentially irreversible changes in the overall environmental conditions we experience on Earth." This is why, for example, it is often said that global warming must be limited to between 1.5º C and 2º C from pre-industrial levels.
Yet the Science Advances study identifies more problems than just climate change. Humanity is causing various degrees of serious risk when it comes to land system change, freshwater change, biosphere integrity, novel entities (like plastics, pesticides, industrial chemicals, etc.) and the flows of biological and geological chemicals. There are only three planetary boundaries where it can be said humanity is still acting within a safe operating space: Ocean acidification, stratospheric ozone depletion and atmospheric aerosol loading. Yet even ocean acidification is "close to being breached," the authors write, while "aerosol loading regionally exceeds the boundary."
"It is clearly in humanity's interest to avoid perturbing Earth system to a degree that risks changing global environmental conditions so markedly," the authors wrote.
The researchers arrived at these conclusions after incorporating the latest scientific research into the body of work that has been accumulated around these topics since 2009. Indeed, for the planetary boundaries framework to be useful, it needs to be periodically updated. Just as a person must monitor their budget to maintain their financial health, so too must they monitor the planet's biophysical boundaries to keep Earth at its healthiest.
"We live by using the Earth's resources and we throw our waste into the open environment," Richardson explained. "The Earth's resources are limited and our demand exceeds their supply. You can party even when your bank account balance is declining — but you cannot party forever and that is the situation humanity has brought itself into."
This is not to say that humanity's outlook is entirely bleak. When asked if policies exist which could shift humanity away from the proverbial edge of extinction, Richardson replied "Absolutely!"
"We are already using too much biomass," Richardson said. "We will continue to use the products of photosynthesis but we need innovation that focuses on creating photosynthesis there where it does not naturally occur (bioreactors, for example)."
Richardson added, "Support should be given to developing Earth system models that better describe the interaction between biological processes and physical processes (climate) if we really want to predict future Earth conditions. The climate crisis cannot be dealt with in isolation from the biodiversity crisis."
One could think of these measures as medications, to use an analogy that Richardson included in the study's press statement: "We can regard it as we do our own blood pressure. A BP over 120/80 is not a guarantee of a heart attack but it increases the risk of one. Therefore, we try to bring it down."
This is not the first study to raise awareness about humanity approaching its planetary limits. A 2022 report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), a United Nations body, found that one million animal and plant species face extinction, as "billions of people in all regions of the world rely on and benefit from the use of wild species for food, medicine, energy, income and many other purposes."
Dr. Marla R. Emery, a scientific advisor for the Norwegian Institute for Nature Research, told Salon by email at the time that policies for improving sustainability must vary from region to region.
"The sustainability of uses of wild species is context specific," Emery explained. Life on our planet is threatened in a number of ways, including through hunting, fishing, gathering, harvesting, economic demands and even "the systems that are in place to regulate and govern their activities," Emery said.
Similarly, a 2021 study published in the peer reviewed journal Communications Earth & Environment found that in many cases, human-caused factors are driving extinction at a rate that surpasses that of the Cretaceous–Paleogene extinction event — that is, the mass extinction 66 million years caused when an asteroid collided with Earth, killing most of the dinosaurs.
By analyzing the extinction rates for freshwater animals and plants, then using that data to extrapolate likely future extinction rates, the researchers learned that the average predicated rate for freshwater animals and plants today is three orders of magnitude higher than it was during the Cretaceous–Paleogene extinction event. At that rate, one-third of all the freshwater species alive right now could be extinct by 2120.
The summer of 2023, which was the hottest in recorded history, served as a potent reminder of the consequences of transgressing planetary limits. According to a study in the journal PNAS, if climate change continues at its current pace there will be so-called compound drought and heatwaves that will happen roughly twice a year for approximately 25 days. They will occur from eastern North America and the American southwest to eastern Africa, Central Europe and Central Asia, and will involve heatwave-caused extreme weather compounding upon itself — such as a heatwave causing droughts, wildfires, severe storms and other consequences. This year alone, the United States has experienced a record-breaking 23 natural disasters exceeding $1 billion in damages — including the Maui wildfires and Hurricane Idalia — and there are still four months left in 2023.
"It's a 'new abnormal' and it is now playing out in real time — the impacts of climate change are upon us in the form of unprecedented, dangerous extreme weather events," study co-author Dr. Michael E. Mann, a professor of Earth and Environmental Science at the University of Pennsylvania, told Salon at the time. "And it will only get worse and worse as long as we continue to burn fossil fuels and generate carbon pollution."
