Twenty-five years ago, scientists issued a warning to humanity that environmental damage must be curbed. In the 1992 statement, the Union of Concerned Scientists and some 1,700 independent scientists said that “a great change in our stewardship of the Earth and the life on it is required, if vast human misery is to be avoided.”

The scientists expressed concern over a number of environmental issues, including the depletion of ozone, freshwater supplies and marine life; deforestation and dead zones in the ocean; a drop in biodiversity; harmful climate change; and unrestrained human population growth.

Trends in environmental issues before and after the 1992 warning. Source: Oxford University Press

Now, Oregon State University ecologist William Ripple and more than 15,000 scientists have released a follow up to the original warning in the journal BioScience. They review the progress (or lack thereof) of humanity’s response to environmental threats, and warn that urgent action is needed to prevent a collapse of the planet’s natural life-sustaining systems.

Climate change is highlighted as the most critical danger. Global temperatures have risen by more than half a degree Celsius since 1992, driven by CO₂ emissions that are up 62 percent.

But many other calamitous issues exist, such as another mass extinction event caused by humans. The number of species of vertebrates, including mammals, reptiles, amphibians and fish has dropped by almost 30 percent since 1992. “Many current life forms could be annihilated or at least committed to extinction by the end of this century,” the scientists said.

Meanwhile, the human population has grown by some 35 percent, adding another 2 billion people to the planet. The pressure created by this growing population threatens to overwhelm Earth’s ecosystems' ability to support the web of life, they say.

The lone bright spot among the list of failures is the shrinking of the hole in the planet’s protective ozone layer to its smallest size since 1988. This is due to restrictions placed on the use of ozone depleting chemicals such as the chlorofluorocarbons previously used in refrigerators and air conditioners. Progress on this issue demonstrates that humanity is capable of addressing environmental challenges.

The scientists suggest 13 actions humanity can take to shift onto a path to sustainability and avoid environmental cataclysm. The steps include creating reserves for wildlife and habitat, encouraging plant-based diets, transitioning to renewable energy sources, phasing out fossil fuel subsidies and establishing a goal for a sustainable human population size.

“Soon it will be too late to shift course away from our failing trajectory, and time is running out,” the scientists say. “We must recognize, in our day-to-day lives and in our governing institutions, that Earth with all its life is our only home.”