*update* April 4, 2013 In Sign of Warming, 1,600 Years of Ice in Andes Melted in 25 Years

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Earth may be near tipping point, scientists warn
A group of international scientists is sounding a global alarm, warning that population growth, climate change and environmental destruction are pushing Earth toward calamitous — and irreversible — biological changes.

In a paper published in Thursday's edition of the journal Nature, 22 researchers from a variety of fields liken the human impact to global events eons ago that caused mass extinctions, permanently altering Earth's biosphere. "Humans are now forcing another such transition, with the potential to transform Earth rapidly and irreversibly into a state unknown in human experience," wrote the authors, who are from the U.S., Europe, Canada and South America.

If current trends continue — exploding global population, rapidly rising temperatures and the clearance of more than 40% of Earth's surface for urban development or agriculture — the planet could reach a tipping point, they say. "The net effects of what we're causing could actually be equivalent to an asteroid striking the Earth in a worst-case scenario," the paper's lead author, Anthony Barnosky, a professor of integrative biology at UC Berkeley, said in an interview. "I don't want to sound like Armageddon. I think the point to be made is that if we just ignore all the warning signs of how we're changing the Earth, the scenario of losses of biodiversity — 75% or more — is not an outlandish scenario at all."

Global population just passed 7 billion and is expected to reach 9.3 billion or more by 2050. "By the year 2070, we'll live in a hotter world than it's been since humans evolved as a species," Barnosky said. Increased carbon dioxide in the atmosphere from the burning of fossil fuels is making the ocean more acidic, and less hospitable to sea life. By midcentury, humans could have altered more than half the world's land surface.

The swiftness of climate change is likely to outpace the ability of species to adapt, especially as natural habitat becomes more fragmented, Barnosky said. All this could produce a biologically impoverished Earth that would rob humans of vital ecological services such as insects that pollinate crops, forests that provide clean water, and tropical species that are the source of new drugs.

"We have created a bubble of human population and economy … that is totally unsustainable and is either going to have to deflate gradually or is going to burst," said co-author James Brown, a distinguished professor of biology at the University of New Mexico. "If it's going to burst, the consequences are really going to be grim for people as well as biodiversity and the rest of the planet."

Forty years ago, the Club of Rome think tank caused a stir when it argued that there were limits to world growth. In 1968, Paul Ehrlich, now a professor of population studies at Stanford University, warned of the dangers of overpopulation in his book "The Population Bomb." "This is what scientists saw in the '60s and '70s," said Mikael Fortelius, a professor of evolutionary paleontology at the University of Helsinki in Finland and one of the paper's authors. "We've never been quite sure when it would happen. We're there now."

Human influence on the planet has become so pervasive that some scientists have argued in recent years that Earth has entered a new geologic epoch, the Anthropocene. "We may have already passed the tipping point or we may not get an early warning" that it is near, said co-author Alan Hastings, an ecologist and distinguished professor in UC Davis' environmental science department.

The authors got the idea for their review at a 2010 UC Berkeley conference devoted to the concept of a global tipping point. They looked at evidence of past dramatic shifts in Earth's biosphere, such as the end of the last glacial age, when ice disappeared from nearly a third of the planet's surface, or the lethal changes in the atmosphere that accompanied periods of intense volcanic activity. The consequences usually included mass species extinction, altered food webs and the emergence of new dominant species.

To avert a grim future, or at least make it less grim, the paper calls for significant reductions in world population growth and per-capita resource use, more efficient energy use, less reliance on fossil fuels and stepped-up efforts to protect the parts of Earth that have so far escaped human dominance.

"I'm not personally particularly optimistic," Fortelius said. "I think we had to speak up. We have to say what we see. Whether it will have any impact, I really don't know."

Rio Earth summit nears as scientists warn planet faces grave threats
As thousands of people prepare to convene in Brazil this month for the Rio+20 Earth Summit, scientists and environmentalists alike are sending a sharp message: The planet is in dire straits.

On Wednesday, the United Nations Environment Program issued a report showing that the world has made significant progress on only four of the 90 most important environmental objectives agreed on through the U.N. process. Gains have come in eliminating ozone-depleting substances, phasing out lead in gasoline, increasing access to water supplies and encouraging research into marine pollutants. In most other categories — including protecting plant and animal species, curbing marine pollution and conserving water supplies — humanity is falling short.

“If current trends continue, if current patterns of production and consumption of natural resources prevail and cannot be reversed and ‘decoupled,’ then governments will preside over unprecedented levels of damage and degradation,” UNEP Executive Director Achim Steiner said in a statement.

The journal Nature published a series of articles Wednesday on the precarious state of the planet, including a study that warns that the world could be approaching a tipping point at which human activities cause a “planetary-scale critical transition” to a different environment.

Twenty years ago, the Rio Earth Summit produced three major treaties intended to head off these kinds of dire outcomes, including the U.N. Framework Convention on Climate Change and the U.N. Convention on Biodiversity. Although the global community has failed to achieve the goals set out by those accords, the meeting was seen as a critical moment at which environmental concerns took center stage in global policymaking.

But even the most prominent proponents of the U.N. Conference on Sustainable Development, which will take place June 20-22 in Rio de Janeiro, do not expect this gathering to produce a significant global agreement. “As things currently stand, we are facing two likely scenarios — an agreement so weak it is meaningless, or complete collapse,” Jim Leape, director general of the World Wildlife Fund, said in a statement Tuesday. “Neither of these options would give the world what it needs.”

“When they gather in Rio, governments must restrain the flow of weasel words that is threatening to emasculate any agreement,” Leape added. “We do need these moments to sit back and reflect on where we are, and where we’re going,” said Frances Beinecke, president of the Natural Resources Defense Council, adding that pledges by world leaders at these meetings often fail to materialize later on. “They don’t translate into action in the way that we would hope.”

In the meantime, however, researchers continue to publish sobering findings. The UNEP report noted that indoor air pollution from fine particles — emitted from cookstoves and other sources — causes nearly 2 million premature deaths a year, including 900,000 deaths in children younger than 5.

The world missed its U.N. target for achieving a significant cut in the loss of species by 2010, it added.

In some ways, global connectivity and rising incomes are helping fuel these problems. One paper Nature published Wednesday, authored by six researchers from Australia, Japan and Italy, found that 30 percent of the threats facing species worldwide stem from international trade, whether it is palm oil production or mining.

The most daunting assessment may have come from a team of 22 scientists from five nations that warned that humans have radically changed 43 percent of the Earth’s surface from its natural state, far outpacing the 30 percent change that helped trigger the last planetary-scale environmental shift roughly 11,000 years ago, when glaciers advanced and then retreated.

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Image courtesy Martin Meissner / Associated Press