The message, posted online, updates an original Warning from the Union of Concerned Scientists and around 1,700 signatories delivered in 1992.
Today, the global scientific community's view of the future is even more bleak.
Apart from the hole in the ozone layer, which has now been stabilised, every one of the major threats identified in 1992 has worsened.
Runaway consumption of precious resources by an exploding population remains the biggest danger facing humankind, say the scientists.
They urge "scientists, media influencers and lay citizens" to put pressure on governments to reverse the trend.
A host of environmental calamities are highlighted in the warning notice, including catastrophic climate change, deforestation, mass species extinction, ocean "dead zones", and lack of access to fresh water.
Writing in the online international journal BioScience, the scientists led by top US ecologist Professor William Ripple, from Oregon State University, said: "Humanity is now being given a second notice ... We are jeopardising our future by not reining in our intense but geographically and demographically uneven material consumption and by not perceiving continued rapid population growth as a primary driver behind many ecological and even societal threats.
"By failing to adequately limit population growth, reassess the role of an economy rooted in growth, reduce greenhouse gases, incentivise renewable energy, protect habitat, restore ecosystems, curb pollution, halt defaunation, and constrain invasive alien species, humanity is not taking the urgent steps needed to safeguard our imperilled biosphere."
In their original warning, scientists including most of the world's Nobel Laureates argued that human impacts on the natural world were likely to lead to "vast human misery".
The new notice, written as an open-letter "viewpoint" article, won the support of 15,364 scientists from 184 countries who agreed to offer their names as signatories.
The authors drew on data from government agencies, non-profit organisations and individual researchers to set out their case that environmental impacts were likely to inflict "substantial and irreversible harm" to the Earth.
Prof Ripple said: "Those who signed this second warning aren't just raising a false alarm. They are acknowledging the obvious signs that we are heading down an unsustainable path.
"We are hoping that our paper will ignite a widespread public debate about the global environment and climate."
Progress had been made in some areas - such as cutting ozone-depleting chemicals, and increasing energy generated from renewable sources - but this was far outweighed by the damaging trends, said the scientists.
They pointed out that in the past 25 years:
:: The amount of fresh water available per head of population worldwide has reduced by 26%.
:: The number of ocean "dead zones" - places where little can live because of pollution and oxygen starvation - has increased by 75%.
:: Nearly 300 million acres of forest have been lost, mostly to make way for agricultural land.
:: Global carbon emissions and average temperatures have shown continued significant increases.
:: Human population has risen by 35%.
:: Collectively the number of mammals, reptiles, amphibians, birds and fish in the world has fallen by 29%.
Prof Ripple and his colleagues have formed a new independent organisation called the Alliance of World Scientists to voice concerns about environmental sustainability and the fate of humanity.