is best defined as human intervention in the way the Earth naturally functions. We have done some unintended geo-engineering over the last 200 years by dumping billions of tons of carbon dioxide into the atmosphere, without concern for the consequent warming of the Earth and all its attendant problems.

In spite of that experience, we are now being urged to set out on one more geo-engineering plan, which will purportedly cool the Earth by injecting a million tons of sulfur dioxide per year into an atmosphere that's already under attack. It is a plan dear to the hearts of the industrial classes, who seek to delay at any cost the only permanent solution to global warming, which is to simply stop burning fossil fuels.

The sulfur dioxide solution is akin to numbing a cancer patient's pain with opiates while still encouraging the cancer to grow. The carbon dioxide emitted by burning fossil fuels is the cancer on our fragile envelope of air. Masking its global-warming effect while continuing to emit the gas can only lead to ever-increasing heat, accompanied by ever-increasing attempts to combat that heat.

This cycle will lead to a variety of bad outcomes, including destruction of the ozone layer and a probable diminution of the world's already inadequate food supply. The food supply depends on how much sunlight and rain fall on the ground, and both would be diminished by sowing sulfur dioxide in the atmosphere. And, as if that weren't bad enough, sulfur dioxide combines with atmospheric water vapor to produce acid rain, so the diminished rainfall would become more destructive.

Inadvisable as it is, the sulfur dioxide solution is the least crazy of geo-engineering's answers to global warming. One suggestion being taken seriously is to deploy mirrors a million miles from Earth, which would reflect some sunlight away from the planet. Given the billions of dollars this wild scheme would cost and the decades it would take to realize - assuming it's even possible - its main effect might be on the climate of the distant future.

Yet another irresponsible scheme calls for deliberately increasing the acidity of the oceans to encourage carbon absorption. Increasing ocean acidity would disrupt the delicate relationships among myriad marine animals that are the basis of our food chain, as well as the seas they live in.

Another proposal is to promote blooms of carbon-eating algae by dumping thousands of tons of iron into the sea. When tried, this approach had the unforeseen consequence of producing a kind of algae that stubbornly refused to include carbon in their diet. And even if the algae-seeding had worked, it would have had to take place over an area the size of the entire Southern Ocean to have a substantial effect on warming.

All of these untried, untestable, and unprovable geo-engineering proposals would have dangerous and possibly fatal unintended consequences - save one. The only example of geo-engineering that we know will work is to start cutting down on the burning of fossil fuels. Only that will begin to reverse the centuries of damage wrought by foolishly carbonizing our atmosphere without a thought to the future.

Every decade we delay replacing fossil energy with something less hurtful to our planet makes it more difficult to assure that the Earth can be kept at a hospitable temperature. And every decade of this profligacy puts an increasingly onerous burden on our children and grandchildren.