WASHINGTON - When climate scientist Andrew Weaver considers the idea of tinkering with Earth's air, water or sunlight to fight global warming, he remembers the lessons of a favorite children's book.
In the book, a cheese-loving king's castle is infested with mice. So the king brings in cats to get rid of the mice. Then the castle's overrun with cats, so he brings in dogs to get rid of them, then lions to get rid of the dogs, elephants to get rid of the lions, and finally, mice to get rid of the elephants.
That scenario in "The King, the Mice and the Cheese," by Nancy and Eric Gurney, should give scientists pause before taking extreme measures to mess with Mother Nature, says Weaver of the University of Victoria.
However, in recent months, several scientists are considering doing just that.
They are exploring global warming solutions that sound wholly far-fetched, including giant artificial "trees" that would filter carbon dioxide out of the air, a bizarre "solar shade" created by a trillion flying saucers that lower Earth's temperature, and a scheme that mimics a volcano by spewing light-reflecting sulfates high in the sky.
These are costly projects of last resort - in case Earth's citizens don't cut back fast enough on greenhouse gas emissions and the worst of the climate predictions appear not too far away. Unfortunately, the solutions could cause problems of their own - beyond their exorbitant costs - including making the arid Middle East even drier and polluting the air enough to increase respiratory illnesses.
Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, said mankind already has harmed Earth's climate inadvertently, so it's foolish to think that people can now fix it with a few drastic measures.
But at Trenberth's same Boulder, Colo., research center, climate scientist Tom Wigley is exploring that mock volcano idea.
"It's the lesser of two evils here (the other being doing nothing)," Wigley said. "Whatever we do, there are bad consequences, but you have to judge the relative badness of all the consequences."
Studying the concept of how volcanic pollutants could lessen global warming - the Earth was slightly cooler after the eruption of a Philippine volcano 16 years ago - was brought to the forefront of scientific debate last summer by Nobel Laureate Paul Crutzen.
"It was meant to startle the policymakers," said Crutzen, of Germany's Max Planck Institute for Chemistry. "If they don't take action much more strongly than they have in the past, then in the end, we have to do experiments like this."
In the past, scientists and others have avoided talking publicly about these ideas, known as "geoengineering," even though the concept was first raised in 1965. They worried that the hope of a quick technological fix to global warming would prevent politicians and the public from making the real energy sacrifices that they say are necessary to slow climate change.
David Keith, a University of Calgary engineering professor and one of the world's experts in geoengineering, says that just because tinkering with the air, water and sunlight are possible, they should not be substitutes for cutting emissions just because "we've been politically weak-kneed."
Instead, he said, such options should be researched as an "insurance policy" in case global warming is even worse than forecast. And that prospect has caused climate scientists to talk about the issue more openly in recent months.
There is also a chance that discussion of such radical ideas as a volcano or sun shade could shock the world into acting to reduce fossil fuel emissions, Keith said.
However, White House science adviser Jack Marburger, said spending money on geoengineering doesn't make sense. The federal government, which spends about $2 billion on climate change science, invests nearly all of its research on energy sources that produce fewer or no greenhouse gas emissions.
"I don't think it's scientifically feasible at this time to consider a plan like that (geoengineering)," Marburger told The Associated Press. "The real urgency is to reduce carbon dioxide."
In 2001, the Intergovernmental Panel on Climate Change looked at geoengineering as part of its report on how to lessen global warming. It found some promise, worried about unexpected side effects, legal and ethical implications, and concluded that "unlike other strategies, geoengineering addresses the symptoms rather than the causes of climate change."
Even proponents of geoengineering research are wary.
"We are playing with fire here," Keith said. "Those of us suggesting we do something are suggesting it with real nervousness."
Associated Press Special Correspondent Charles J. Hanley in New York contributed to this report.