How Deadly for Your Child -- or World?

Aug. 29, 2006 — -- If a trusted board of experts told you there was a 65 percent chance that poison was laced into the food on the plate in front of your child, would you say, "Go ahead and eat"?

You'd grab your kid and be out of there.

The Hurricane Katrina anniversary, scientists say, may mark a similar watershed for caution in the American public.

Katrina seems to be the event that impressed people, not so much with the threat of global warming but with the gravity of that threat.

The science linking human-induced global warming to a rising severity in hurricanes may not be 100 percent, but for a year, the public has been hearing scientists -- and other commentators, including Al Gore and a growing number of editors -- report that there could well be such a link.

Most credible scientists suggest the likelihood of manmade global warming greatly altering life on Earth -- and quite possibly within the lifetime of today's toddlers, if we keep burning coal, gas and oil unchecked -- is far above 65 percent, and more likely somewhere in the upper 90's percentiles.

The Post-Katrina Era

"Post-Katrina" is a phrase now used by scientists and other observers to describe a new public awareness of just how serious the global warming threat may be.

The ghastly spectacle of Katrina-soaked New Orleans, linked even tentatively to climate change, somehow made real the potential of global warming to bring death and disease, to unhinge our way of life and overwhelm government.

Where is that scientific debate now?

"Science linking worsening hurricanes to global warming has advanced significantly in the past year," says global warming analyst and author Susan Joy Hassol, a 20-year veteran of the struggle to communicate climate science to the English-speaking world.

Hassol cites a dozen different studies, the first by MIT professor Kerry Emanuel, published a month before Katrina, that found a spike in sea-surface temperatures over the past 30 years that fit exactly with a spike in the intensification and lengthening of hurricanes over the same period.

The second study, published a month after Katrina, by Peter Webster et al, found that while the total number of hurricanes around the world had remained the same over the past 35 years, the number reaching Category 4 or 5 had nearly doubled -- and this during a period in which the global tropical sea surface temperatures (already closely linked to manmade warming) rose nearly a degree (doesn't sound like much, but as a global average, scientists say, it's major).

Leading hurricane researchers tell ABC News one reason these two breakthrough studies carry such weight among them is that their authors were trying, in the best skeptical tradition, to disprove a link to global warming but were overwhelmed by the evidence.

There are still a few holdouts among American hurricane scientists. Colorado State University's William Gray and one of his former students, Chris Landsea at the National Hurricane Center, argue that the data are not good enough from earlier decades even to claim with certainty a significant global worsening of hurricanes.

"I'm not so much arguing that there might not be some worsening from global warming," Landsea tells ABC News in a phone interview, "but my question is, how much?" He cites figures suggesting it could be very little and that hurricanes may intensify at most only by 5 percent by the end of the century.

"One thing that does kind of scare me," says Landsea, "is that we are doing an experiment on Earth."

A Global Experiment Gone Wrong?

We have found this fear -- about experimenting with greenhouse gas emissions on our only planet -- to be virtually universal among scientists, whatever their intramural debates on the degree and mode of the warming.

Take the worries about "the final tipping point."

That's the temperature -- it's hoped higher than we're at now -- at which the immense reservoirs of natural greenhouse gases, frozen and otherwise trapped in the ground and seabeds, thaw and rise into the atmosphere.

That would quickly heat Earth to temperatures far higher than humans have ever experienced, say scientists.

Those reservoirs include untold stores in the seabeds of the greenhouse gas methane, trapped in "clathrates" -- a kind of icy mud with an unearthly blue-white tinge.

"There's a lot we don't know about the methane clathrate story," says NASA's Gavin Schmidt, who specializes in computer modeling of climate scenarios present and past.

Schmidt and Jerry Dickens, a professor at Rice University in Texas, both study 55 million-year-old cores of mud drilled from ocean floors around the world.

That mud tells a remarkable story, they say, when scientists analyze its molecules.

"In one period back then, a stretch of about 10 [thousand] to 20 thousand years," says Dickens, "something sent a lot of natural greenhouse gas, probably methane, into the atmosphere."

The muddy molecules, he and Schmidt tell ABC News, show that immediately after that, Earth's temperature rose sharply by about 10 to 20 degrees Fahrenheit -- far greater than the human-induced warming we've experienced in the past century.

"The key issue," says Dickens, "is that the rate of warming is now 10 to 20 times faster than what happened 55 million years ago."

"We are running an experiment on Earth similar to past events on Earth," he told us.

"We don't know what results there will be this time, but in the past, they were dramatic."