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Is nature one mean mother?

A color-coded image from NASA's Aqua satellite

shows levels of outgoing long-wave radiation

during the deadly European heat wave of 2003.

Swine flu?Global warming?Toxic oceans? Why does Mother Nature sometimes seem to be on the attack? According to the decades-old "Gaia hypothesis," it's because Earth is a self-regulating system that is responding to our own excesses. In a new book titled "The Vanishing Face of Gaia," British biologist James Lovelock says humanity is "Earth's infection."

"Individuals occasionally suffer a disease called polycythaemia, an overpopulation of red blood cells. By analogy, Gaia's illness could be called polyanthroponemia, where humans overpopulate until they do more harm than good," Lovelock writes. He says the cure won't come until the human tribe is trimmed back from its current 6.8 billion to, say, 1 billion people.

Now University of Washington paleontologist Peter Ward has proposed an alternate theory that suggests Earth is set up to kill off life when it spreads too widely. Humans wouldn't be the first victims of this periodic biocide. The dinosaurs may have been killed off by an asteroid, he says, but during the planet's other mass extinctions, millions of species were done in by good old Mom.

"I hypothesize that life and its processes, together often referred to as 'Mother Nature,' was, is, and will be anything but a good mother to her many evolved and evolving species," Ward contends in his new book, "The Medea Hypothesis."

Gaia vs. Medea ... that sounds like the start of a philosophical catfight.

Ward, however, says he's not just trying to pick a fight with the 90-year-old Lovelock. "Most every scientist is trying to 'pick a fight' with another scientist," he told me today. "We try to do it in a collegial fashion. ... I'm trying to do science, but I'm also trying to point out that there has never been opposition in a formal sense - it's been Gaia, Gaia, nothing but Gaia."

Actually, Ward agrees with Lovelock that the world is facing an increasingly imminent crisis over climate change. The sharp rise in global average temperatures seems certain to lead to an unstoppable rise in sea levels that will change our coastlines, cities and croplands, Ward said. (He'll address this subject in depth, so to speak, in his next book, "The Flooded Earth.")

"The short term is a nasty, nasty situation," Ward said. "Where we differ is in his sense that if humans would somehow go away, there would be this natural, pristine world."

The way Ward sees it, we're the solution, not the problem. "In the short term, we are responsible for 'Medean' effects, but it's going to be our long-term stewardship and engineering that makes things work," he said. "I view humans as the only Gaians on the planet. Everything else is Medean."

While Lovelock uses "Gaia" to refer to Earth's biosphere as a kindly mother goddess, Ward uses "Medea" as a reference to the mother in Greek myth who killed her own children. Ward says life, like Medea, eventually sows the seeds of its own near-destruction - over and over again. "Life boils up and bubbles up, and through its own waste products and activities makes the planet no longer inhabitable," he said.

Medea's weapon of choice is the interaction between the atmosphere, oceans and land, Ward said. For years, he has contended that climate set off history's biggest-ever die-off, the Permian-Triassic extinction that occurred 250 million years ago.

Ward's "rotten-eggstinction" scenario begins with a shift in climate that sparks blooms of sulfur-loving microbes in the world's oceans. Their belches of hydrogen sulfide - the gas commonly associated with rotten eggs - triggers a sequence of events that end with a global poisoning of marine and land species. (This scenario is detailed in Ward's previous book, "Under a Green Sky.")

In "The Medea Hypothesis," Ward sketches out similar biocidal scenarios for other extinction events. He goes with the conventional wisdom that a huge asteroid touched off the Cretaceous-Tertiary extinction that killed off the dinosaurs, but says continent-spanning forest fires most likely sparked a global winter that finished the job. Thus, he writes, "it could be argued that the effects of life magnified the extent of the extinction."

The current swine-flu outbreak may not come anywhere close to these past bio-crises, but it does demonstrate that Mother Nature can have some nasty surprises in store. "This is another case showing that evolution works really quickly on microbes," Ward said. "It also underscores the fact that microbes are our biggest enemy on Earth."

Today, there are fresh signs of a rotten-egg uprising, such as a recent eruption of hydrogen sulfide off the coast of Namibia. And it's not just Namibia: Ward pointed to research conducted in the waters of Washington state's Commencement Bay, where high sulfide concentrations are hammering marine seagrass.

"It may be we are just starting to see the first effects of this poisoning of seagrass," he said. And that's just the first link in the chain. "Seagrass is where the herring breed," Ward noted.

So what is to be done? Ward says humans will have to engineer new ways to cope with a mad mother - for example, to counter rising carbon dioxide levels in the short run. By the way, Ward defines the "short run" as lasting more than 3,000 years. (What did you expect? He's a paleontologist, not a stockbroker.)

In the long run, over the course of many, many thousands of years, "the engineering challenge will be getting carbon back into the atmosphere," Ward writes in his book's final chapter:

"Even with an enlarging sun, the long-term drop in CO2 as it is put into storage within contenental rock poses the most significant threat to planetary biomass. No plants means no oxygen, so we will require ever present efforts to move carbon from limestones and other continental rocks back into the atmosphere. This is relatively simple, as we know now - burn hydrocarbons. But as these will ultimately be used up, some kind of heating of limestones on a massive scale will do the trick."

By that time, won't we be moving on (and despoiling) a new home in outer space? "That may not be an option," Ward told me. In his view, the costs and distances involved in moving outward from the solar system - or even terraforming the moon or Mars - just don't seem worth the effort.

On this point, Ward and Lovelock seem to agree: Whether she's good or bad, we're pretty much stuck with the mother we were born with.

"The only 'out' is intelligence," Ward said. "Our intelligence is the only way that we can extend the longevity of the biosphere."