Tipping point before planetary collapse ‘is only decades away’

They called for drastic action, such as rapid curbs on population growth, to prevent food supplies being threatened by major changes to farming caused by climate change.

A team of 22 scientists reached the conclusion by comparing the biological impact of past major global changes with current patterns.

The warning comes two weeks before the United Nations Earth Summit in Rio de Janeiro, which marks the 20th anniversary of the landmark Brazil meeting.

According to the researchers, the report contradicted the belief that global collapse would be gradual or centuries away.

Anthony Barnosky, professor of integrative biology at the University of California, Berkeley, who led the research, said: “There will be a reduction in biodiversity and severe impacts on much of what we depend on to sustain our quality of life, including fisheries, agriculture, forest products and clean water.

“This could happen within just a few generations. The root cause, ultimately, is human population growth and how many resources each one of us uses.”

The scientists called for fundamental changes to lifestyles. Report co-author Arne Mooers, of Simon Fraser University in British Columbia, said: “Society globally has to collectively decide that we need to drastically lower our population very quickly.”

He said more people had to move to urban areas to let parts of the planet recover and added: “Folks like us have to be forced to be materially poorer, at least in the short term.”

The report, published in the journal Nature, admitted it was not known how close Earth was to the tipping point, or whether it was inevitable.

Professor Barnosky said this would become “disturbingly close” by 2025 when the proportion of land used for farming or homes is forecast to rise from 43 to 50 per cent. He said: “I think if we want to avoid the most unpleasant surprises, we want to stay away from that 50 per cent mark.”

Co-author Elizabeth Hadley, of Stanford University in California, added: “We may already be past these tipping points in particular regions of the world.

“I just returned from the high Himalayas in Nepal, where I witnessed families fighting each other with machetes for wood – wood that they would burn to cook their food one evening.” Prof Barnosky said if nothing was done, humanity would probably survive, “but we are going to see some effects that will seriously degrade the quality of life for our children and grandchildren”.

Environmental campaigners WWF Scotland said the report underlined the importance of Scotland playing its part.

Director Richard Dixon said: “This study warns climate change could drive humanity, and many of the species which share the planet with us, over the edge.

“Millions of people, especially poor people, are already feeling the impacts of climate change but Scotland has been largely unaffected so far. This study shows nowhere is safe if we reach a drastic tipping point. This is a timely warning.

“Our Scottish environment and climate minister will be going to the Rio+20 conference in two weeks’ time to talk about our climate targets.

“Promoting this good example is much needed.”