Last year, a private company proposed "fertilizing" parts of the ocean with iron, in hopes of encouraging carbon-absorbing blooms of plankton. Meanwhile, researchers elsewhere are talking about injecting chemicals into the atmosphere, launching sun-reflecting mirrors into stationary orbit above the earth or taking other steps to reset the thermostat of a warming planet.

This technology might be useful, even life-saving. But it would inevitably produce environmental effects impossible to predict and impossible to undo. So a growing number of experts say it is time for broad discussion of how and by whom it should be used, or if it should be tried at all.

Similar questions are being raised about nanotechnology, robotics and other powerful emerging technologies. There are even those who suggest humanity should collectively decide to turn away from some new technologies as inherently dangerous.

"The complexity of newly engineered systems coupled with their potential impact on lives, the environment, etc., raise a set of ethical issues that engineers had not been thinking about," said William Wulf, a computer scientist who until last year headed the National Academy of Engineering. As one of his official last acts, he established the Center for Engineering, Ethics and Society there.

Rachelle Hollander, a philosopher who directs the center, said the new technologies were so powerful that "our saving grace, our inability to affect things at a planetary level, is being lost to us," as human-induced climate change is demonstrating. Today in Health & Science Sorting out coffee's contradictions Vulnerable to HIV, resistant to labels In AIDS fight, governments neglecting behavioral efforts

Engineers, scientists, philosophers, ethicists and lawyers are taking up the issue in scholarly journals, online discussions and conferences around the world.

"It's a hot topic," said Ronald Arkin, a computer scientist at Georgia Tech who advises the U.S. Army on robot weapons. "We need at least to think about what we are doing while we are doing it, to be aware of the consequences of our research."

So far, though, most scholarly conversation about these issues has been "piecemeal," said Andrew Maynard, chief science adviser for the Project on Emerging Nanotechnologies at the Woodrow Wilson Center in Washington. "It leaves the door open for people to do something that is going to cause long-term problems."

That's what some environmentalists said they feared when Planktos, a California company, announced it would embark on a private effort to fertilize part of the South Atlantic with iron in hopes of producing carbon-absorbing plankton blooms that the company could market as carbon offsets. Countries bound by the London Convention, an international treaty governing dumping at sea, issued a "statement of concern" about the work, and a UN group called for a moratorium, but it is not clear what would have happened had Planktos not abandoned the effort for lack of money.

"There is no one to say 'thou shalt not,"' said Jane Lubchenco, an environmental scientist at Oregon State University and a former president of the American Association for the Advancement of Science.

When scientists and engineers discuss geoengineering, it is obvious they are talking about technologies with the potential to change the planet. But the issue of engineering ethics applies as well to technologies whose planet-altering potential may not emerge until it is too late.

Arkin said robotics researchers should consider not just how to make robots more capable, but also who must bear responsibility for their actions and how much human operators should remain "in the loop," particularly with machines to aid soldiers on the battlefield or the disabled in their homes.

But he added that progress in robotics was so "insidious" that people might not realize they had ventured into ethically challenging territory until too late.

Ethical and philosophical issues have long occupied biotechnology, where institutional review boards commonly rule on proposed experiments and advisory committees must approve the use of gene-splicing and related techniques. When the U.S. government initiated its effort to decipher the human genome, a percentage of the budget went to consideration of ethics issues like genetic discrimination.

But such questions are relatively new for scientists and engineers in other fields. Some are calling for the same kind of discussion that microbiologists organized in 1975 when the immense power of their emerging knowledge of gene-splicing or recombinant DNA began to dawn on them. The meeting, at the Asilomar conference center in California, gave rise to an ethical framework that still prevails in biotechnology.

"Something like Asilomar might be very important," said Andrew Light, director of the Center for Global Ethics at George Mason University, one of the organizers of a conference in Charlotte, North Carolina, in April on the ethics of emerging technologies. "The question now is how best to begin that discussion among the scientists, to encourage them to do something like this, then figure out what would be the right mechanism, who would fund it, what form would recommendations take, all those details."

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