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In November 2017, more than 15,000 scientists from 184 countries backed a short paper in the journal BioScience titled "World Scientists' Warning to Humanity: A Second Notice". Led by ecologist William J. Ripple of Oregon State University, it looked back at a famous 1992 warning, checked what had happened to the planet in the 25 years since, and concluded that on most measures things had got worse. It also listed practical steps that could still turn the trend around.
This guide explains what the warning said, the evidence behind it, what had improved, what the scientists asked for, and how the story has continued since.
The first warning, in 1992
The original "World Scientists' Warning to Humanity" was written by physicist Henry W. Kendall, a Nobel laureate and former chair of the Union of Concerned Scientists. Around 1,700 leading researchers signed it, including most of the living Nobel Prize winners in the sciences at the time. Its opening line set the tone: "Human beings and the natural world are on a collision course."
The 1992 text warned about ozone depletion, freshwater scarcity, collapsing fisheries, ocean dead zones, forest loss, the decline of species, climate change and continued rapid population growth. It called for a move away from fossil fuels, better management of resources and a stable human population.
What the 2017 second notice measured
Rather than restating fears, the 2017 authors went back to the same issues and plotted data on each one from 1992 onward. The paper includes nine time-series graphs. According to Oregon State University's summary, between 1992 and 2017:
- fresh water available per person fell by 26%;
- the number of ocean dead zones, areas with too little oxygen for most marine life, rose by 75%;
- nearly 300 million acres (about 120 million hectares) of forest were lost, much of it cleared for farming;
- populations of mammals, reptiles, amphibians, birds and fish fell by 29% overall;
- carbon emissions and average temperatures kept rising significantly;
- the human population grew by 35%, adding about two billion people.
Most of these trends were moving in the wrong direction, and in most cases there was no sign that the rate of change was slowing.
The one clear success: the ozone layer
One indicator stood out. Emissions of ozone-depleting chemicals had dropped sharply and the ozone problem had stabilised, thanks largely to the 1987 Montreal Protocol, which phased out CFCs and related compounds. The authors also pointed to falling poverty and hunger in some regions, slowing fertility rates in places with better education for women, and fast growth in renewable energy.
Those examples matter. The warning was meant to show that coordinated action works, not to claim that the outcome was already settled. The ozone story is the clearest proof the authors had that the world can identify a global environmental problem and largely fix it.
What the scientists asked for
The second notice proposed thirteen broad steps toward sustainability. Among the most prominent were:
- creating more protected areas on land and at sea;
- tougher enforcement against poaching and the illegal wildlife trade;
- expanding family planning and education, especially for women and girls;
- shifting diets toward mostly plant-based foods and cutting food waste;
- adopting renewable energy and other green technologies on a large scale, while phasing out fossil fuel subsidies;
- reducing per-person consumption of fossil fuels, meat and other resources in wealthy countries.
The paper drew more co-signers and formal supporters than any journal article before it. That broad backing showed how widely the concerns were shared, though the strength of each specific claim still rests on the data behind it, not on the number of names.
Is a sixth mass extinction really under way?
The 2017 notice said humanity had "unleashed a mass extinction event," the sixth in about 540 million years. In the same year, a separate study by Gerardo Ceballos, Paul Ehrlich and Rodolfo Dirzo in PNAS used the phrase "biological annihilation" to describe widespread population losses among vertebrates.
Scientists broadly agree that species are disappearing far faster than the natural background rate. Where they differ is on the label. Palaeontologists define a mass extinction as the loss of at least three-quarters of species in a geologically short time. Some researchers say the current crisis is already one; others, such as conservation biologist Stuart Pimm, say we are on the edge of it but have not yet reached that point. Both camps agree on the direction of travel, and the 2019 global assessment by the UN biodiversity panel IPBES estimated that around one million species are at risk of extinction, many within decades.
A common misreading is that the warning set a deadline for the end of the world. It did not. It described trends and argued that the longer action is delayed, the harder and more expensive it becomes.
What has happened since 2017
The second notice became the start of a series. In 2019, more than 11,000 scientists from 153 countries backed a follow-up declaring a climate emergency. Ripple and colleagues then began publishing annual "state of the climate" reports in BioScience that track the planet's vital signs.
The sixth of these reports, released at the end of October 2025, found 22 of 34 indicators at record levels. It noted that 2024 had overtaken 2023 as the hottest year on record, that ocean heat and fire-driven tree cover loss had hit all-time highs, and that warming appeared to be speeding up. Yet it also argued that a liveable future is still within reach, through rapid cuts in fossil fuel use, lower consumption in the richest groups, and economies built around reuse and well-being rather than endless growth. Ripple summed it up in a single line, telling Eos that the climate cannot be fixed "by technology alone."
What the warning means for everyday choices
The 2017 notice asked for change both in governments and in daily life. Its final paragraph called on people to recognise, in their own lives and in their institutions, that Earth is our only home. In practice, the actions it highlighted that individuals can influence include eating more plant-based food, wasting less, choosing smaller families where that is a free choice, supporting protected areas, and backing leaders and businesses that move toward clean energy.
None of these alone will settle the problem, and the authors were clear that systems matter more than any single household. But the ozone recovery shows that when public pressure, science and policy line up, the curve can bend.
Sources: BioScience: World Scientists' Warning to Humanity: A Second Notice (2017); Oregon State University: 15,000 scientists in 184 countries warn about negative global environmental trends; Wikipedia: World Scientists' Warning to Humanity; Wikipedia: Holocene extinction; Eos: 2025 state of the climate report (29 October 2025). Story first shared by The Mind Unleashed.
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