They don't use the word doomsday, but they come close.
"Humans now dominate Earth, changing it in ways that threaten its ability to sustain us and other species," the researchers report Thursday in the journal Nature.
The researchers stress it is not known how close Earth is to a global tipping point, or if it is inevitable.
But they suggest that the planet's ecosystems could shift into a new state within just a few decades or a few generations if human population and consumption rates continue to soar.
"It really will be a new world, biologically, at that point," says lead author Anthony Barnosky, professor of integrative biology at the University of California, Berkeley.
Or, as Canadian co-author Arne Mooers, at Simon Fraser Univeristy in British Columbia, puts it: "Once the shift occurs, they'll be no going back."
A shift or tipping point is "speculation at this point," Mooers told Postmedia News.
"But it's one of those things where you say: 'Hey, maybe we better find out,' because if it's true, it's pretty serious."
The Nature paper grew out of a 2010 conference that raised plenty of questions about whether humans could trigger a state shift, but few answers on how to recognize and avoid it.
The 22 biologists, ecologists, theoreticians, geologists and paleontologists who produced Thursday's report reviewed past stateshifts — the latest being end of the most recent ice age — and the remarkable changes humans are driving on the planet.
The climate is warming so fast that the "mean global temperature by 2070 (or possibly a few decades earlier) will be higher than it has been since the human species evolved," they say.
And to support the current population of seven billion people, about 43 per cent of Earth's land surface has been converted to agricultural or urban use. The population is expected to hit nine billion by 2045 and they say current trends suggest that half Earth's land surface will be altered by humans by 2025.
That's "disturbingly close" to a potential global tipping point, Barnosky says in a release issued with the report. The study says tipping points tend to occur when 50 to 90 per cent of smaller ecosystems have been disrupted.
"I think that if we want to avoid the most unpleasant surprises, we want to stay away from that 50 per cent mark," Barnosky says.
The "ultimate effects" of a state shift are unknown, but the researchers suggest it could have severe impact on the world's fisheries, agriculture, forests and water resources. And they warn that "widespread social unrest, economic instability and loss of human life could result."
Mooers says it is known the biosphere is changing because of human activity. "It's a question of whether it is going to be manageable change or abrupt change," he says. "And we have reason to be the change may be abrupt and surprising."
Mooers says he hopes that they are proven wrong. "It would be great if the naysayers were right, I wouldn't have to worry.
"But there is no evidence to suggest they are right," he says. "The evidence is the opposite."
The report is one of series of papers in Nature this week on the huge challenges facing international leaders and delegates gathering in Rio de Janeiro on June 20 for the United Nations Conference on Sustainable Development, known as Rio+20. It is the 20th anniversary of 1992 Earth Summit in Rio.
The journal notes there has been little progress on key international commitments made 20 years ago.
Instead of curbing carbon emissions to try slow climate change, global greenhouse emissions have soared 45 per cent since 1990. And governments are nowhere near meeting 20-year-old pledges to better protect biodiversity — 30 per cent of amphibians, 21 per cent of birds and 25 per cent of mammals are at risk of extinction, according to the International Union for Conservation of Nature.
Original Article
Source: montreal gazette
Author: Margaret Munro
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