Paris (AFP) - Humanity faces "untold suffering" if it fails to tackle the "climate emergency" threatening life on Earth, more than 11,000 scientists warned Tuesday.
In a declaration in the journal BioScience, they noted that 40 years ago, scientists from 50 nations at the first World Climate Change Conference "agreed that alarming trends... made it urgently necessary to act".
But despite repeated warnings and a growing body of evidence, greenhouse gas emissions responsible for global warming "are still rapidly rising, with increasingly damaging effects on the Earth's climate."
"An immense increase of scale in endeavours to conserve our biosphere is needed to avoid untold suffering," the scientists said in BioScience, a peer-reviewed publication of the American Institute of Biological Sciences.
Humanity's expanding numbers, appetites and activities have fuelled the problem, originally in the developed world but now on a global scale.
Burning fossil fuels for energy and industry, forest loss, intensive agriculture and growing livestock populations were singled out as the main drivers.
Warning signs have flashed red for nearly three decades, and yet, "with few exceptions we have generally conducted business as usual", the declaration said.
The scientists recommended six basic steps, starting with massive energy and conservation measures aimed at reducing fossil fuel use and pollution.
The natural environment must be preserved, with forests playing a key role as carbon sinks. Switching to a mostly plant-based diet would also help slash emissions.
On the economy, they note, human beings face a radical choice between continued high-consumption growth and "improving human well-being by prioritising basic needs and reducing inequality".
Finally, population increase -- currently running at 80 million people a year -- should be rapidly stabilised and reduced.
The paper was written by scientists from the University of Sydney, Oregon State University, the University of Cape Town and Tufts University, and then signed by more than 11,000 of their peers under the headline: "World Scientists Warning of a Climate Emergency."