An interdisciplinary group of 22 scientists, combining paleontological evidence with ecological modeling, has concluded that the earth appears headed toward catastrophic and irreversible environmental changes.
Their report, in the June 7 issue of the journal Nature, describes an exponentially increasing rate of species extinctions, extreme climate fluctuations, and other threats that together risk a level of upheaval not seen since the large-scale extinctions 65 million years ago that killed off the dinosaurs.
The lead author of the report is Anthony D. Barnosky, a professor of integrative biology at the University of California at Berkeley, which coordinated the work in an 18-month project that inaugurated the university's Berkeley Initiative in Global Change Biology.
The report's conclusions center on a measure of the amount of the earth's land surface that has been transformed by people, from forests and prairies to uses such as cornfields and parking lots. The percentage of transformed land now stands at 43 percent, with the world's population at seven billion.
The scientists contributing to the report have calculated the various forms of damage that will be seen when the usage level exceeds 50 percent, as is expected around 2025, when the population reaches eight billion, Mr. Barnosky said. The scientists making those estimates include biologists, ecologists, geologists, paleontologists, and complex-systems theoreticians in the United States, Canada, South America, and Europe.
Their conclusion is that the damaging effects, when combined, appear even worse than each of the experts has seen in his or her own field, Mr. Barnosky said. "These are all driving forces that in fact are greater than what we saw in the past," he said.
The size of the problems demands a global response, Mr. Barnosky said. "The only way out of them is cooperation between nations, between individuals on a global basis," he said.
Yet he acknowledged that in a nation with sharp political divisions, including over environmental issues, the report may not garner much attention. "I don't know how much it will sway the people who are just not inclined to believe any of this stuff anyway, who just basically will put their heads in the sand and say, Let's go on with business as usual," he said.
The authors of the report, in fact, make clear that they cannot be totally sure when the earth's environment will reach a "tipping point" beyond which recovery to anything resembling current conditions will be impossible, or even if that will happen. "That's the usual scientific covering-all-your-bases" statement, Mr. Barnosky said.
But for others, the warning contained in the Berkeley-led report may not be strong enough. "I suspect it's a little too optimistic," said Paul R. Ehrlich, a professor of population studies at Stanford University known for his 1968 book The Population Bomb.
Mr. Ehrlich said he foresees a series of dire threats to humanity, many virtually untouched by political leaders, including climate change, water shortages, and the widespread use of man-made toxins. Even a single repercussion of one of those, such as water scarcity leading to nuclear war between India and Pakistan, could devastate populations worldwide, he said.
"Generally the scientific community has spoken many times," Mr. Ehrlich said, "but nobody's paying any attention."