No one can say exactly what it looks like when a planet takes ill,
but it probably looks a lot like Earth. Never mind what you’ve heard
about global warming as a slow-motion emergency that would take decades
to play out. Suddenly and unexpectedly, the crisis is upon us.

It certainly looked that way last week as the atmospheric bomb that
was Cyclone Larry–a Category 5 storm with wind bursts that reached 180
m.p.h.–exploded through northeastern Australia. It certainly looked
that way last year as curtains of fire and dust turned the skies of
Indonesia orange, thanks to drought-fueled blazes sweeping the island
nation. It certainly looks that way as sections of ice the size of
small states calve from the disintegrating Arctic and Antarctic. And it
certainly looks that way as the sodden wreckage of New Orleans
continues to molder, while the waters of the Atlantic gather themselves
for a new hurricane season just two months away. Disasters have always
been with us and surely always will be. But when they hit this hard and
come this fast–when the emergency becomes commonplace–something has
gone grievously wrong. That something is global warming.

The image of Earth as organism–famously dubbed Gaia by
environmentalist James Lovelock– has probably been overworked, but
that’s not to say the planet can’t behave like a living thing, and
these days, it’s a living thing fighting a fever. From heat waves to
storms to floods to fires to massive glacial melts, the global climate
seems to be crashing around us. Scientists have been calling this shot
for decades. This is precisely what they have been warning would happen
if we continued pumping greenhouse gases into the atmosphere, trapping
the heat that flows in from the sun and raising global temperatures.

Environmentalists and lawmakers spent years shouting at one another
about whether the grim forecasts were true, but in the past five years
or so, the serious debate has quietly ended. Global warming, even most
skeptics have concluded, is the real deal, and human activity has been
causing it. If there was any consolation, it was that the glacial pace
of nature would give us decades or even centuries to sort out the
problem.

But glaciers, it turns out, can move with surprising speed, and so
can nature. What few people reckoned on was that global climate systems
are booby-trapped with tipping points and feedback loops, thresholds
past which the slow creep of environmental decay gives way to sudden
and self-perpetuating collapse. Pump enough CO2 into the sky, and that
last part per million of greenhouse gas behaves like the 212th degree
Fahrenheit that turns a pot of hot water into a plume of billowing
steam. Melt enough Greenland ice, and you reach the point at which
you’re not simply dripping meltwater into the sea but dumping whole
glaciers. By one recent measure, several Greenland ice sheets have
doubled their rate of slide, and just last week the journal Science
published a study suggesting that by the end of the century, the world
could be locked in to an eventual rise in sea levels of as much as 20
ft. Nature, it seems, has finally got a bellyful of us.

“Things are happening a lot faster than anyone predicted,” says Bill
Chameides, chief scientist for the advocacy group Environmental Defense
and a former professor of atmospheric chemistry. “The last 12 months
have been alarming.” Adds Ruth Curry of the Woods Hole Oceanographic
Institution in Massachusetts: “The ripple through the scientific
community is palpable.”

And it’s not just scientists who are taking notice. Even as nature
crosses its tipping points, the public seems to have reached its own.
For years, popular skepticism about climatological science stood in the
way of addressing the problem, but the naysayers–many of whom were on
the payroll of energy companies–have become an increasingly
marginalized breed. In a new TIME/ ABC News/ Stanford University poll,
85% of respondents agree that global warming probably is happening.
Moreover, most respondents say they want some action taken. Of those
polled, 87% believe the government should either encourage or require
lowering of power-plant emissions, and 85% think something should be
done to get cars to use less gasoline. Even Evangelical Christians,
once one of the most reliable columns in the conservative base, are
demanding action, most notably in February, when 86 Christian leaders
formed the Evangelical Climate Initiative, demanding that Congress
regulate greenhouse gases.

A collection of new global-warming books is hitting the shelves in
response to that awakening interest, followed closely by TV and
theatrical documentaries. The most notable of them is An Inconvenient
Truth, due out in May, a profile of former Vice President Al Gore and
his climate-change work, which is generating a lot of prerelease buzz
over an unlikely topic and an equally unlikely star. For all its lack
of Hollywood flash, the film compensates by conveying both the hard
science of global warming and Gore’s particular passion.

Such public stirrings are at last getting the attention of
politicians and business leaders, who may not always respond to science
but have a keen nose for where votes and profits lie. State and local
lawmakers have started taking action to curb emissions, and major
corporations are doing the same. Wal-Mart has begun installing wind
turbines on its stores to generate electricity and is talking about
putting solar reflectors over its parking lots. HSBC, the world’s
second largest bank, has pledged to neutralize its carbon output by
investing in wind farms and other green projects. Even President Bush,
hardly a favorite of greens, now acknowledges climate change and boasts
of the steps he is taking to fight it. Most of those steps, however,
involve research and voluntary emissions controls, not exactly the laws
with teeth scientists are calling for.

Is it too late to reverse the changes global warming has wrought?
That’s still not clear. Reducing our emissions output year to year is
hard enough. Getting it low enough so that the atmosphere can heal is a
multigenerational commitment. “Ecosystems are usually able to maintain
themselves,” says Terry Chapin, a biologist and professor of ecology at
the University of Alaska, Fairbanks. “But eventually they get pushed to
the limit of tolerance.”

CO2 AND THE POLES

As a tiny component of our atmosphere, carbon dioxide helped warm
Earth to comfort levels we are all used to. But too much of it does an
awful lot of damage. The gas represents just a few hundred parts per
million (p.p.m.) in the overall air blanket, but they’re powerful parts
because they allow sunlight to stream in but prevent much of the heat
from radiating back out. During the last ice age, the atmosphere’s CO2
concentration was just 180 p.p.m., putting Earth into a deep freeze.
After the glaciers retreated but before the dawn of the modern era, the
total had risen to a comfortable 280 p.p.m. In just the past century
and a half, we have pushed the level to 381 p.p.m., and we’re feeling
the effects. Of the 20 hottest years on record, 19 occurred in the
1980s or later. According to NASA scientists, 2005 was one of the
hottest years in more than a century.

It’s at the North and South poles that those steambath conditions
are felt particularly acutely, with glaciers and ice caps crumbling to
slush. Once the thaw begins, a number of mechanisms kick in to keep it
going. Greenland is a vivid example. Late last year, glaciologist Eric
Rignot of the Jet Propulsion Laboratory in Pasadena, Calif., and Pannir
Kanagaratnam, a research assistant professor at the University of
Kansas, analyzed data from Canadian and European satellites and found
that Greenland ice is not just melting but doing so more than twice as
fast, with 53 cu. mi. draining away into the sea last year alone,
compared with 22 cu. mi. in 1996. A cubic mile of water is about five
times the amount Los Angeles uses in a year.

Dumping that much water into the ocean is a very dangerous thing.
Icebergs don’t raise sea levels when they melt because they’re
floating, which means they have displaced all the water they’re ever
going to. But ice on land, like Greenland’s, is a different matter.
Pour that into oceans that are already rising (because warm water
expands), and you deluge shorelines. By some estimates, the entire
Greenland ice sheet would be enough to raise global sea levels 23 ft.,
swallowing up large parts of coastal Florida and most of Bangladesh.
The Antarctic holds enough ice to raise sea levels more than 215 ft.

FEEDBACK LOOPS

One of the reasons the loss of the planet’s ice cover is
accelerating is that as the poles’ bright white surface shrinks, it
changes the relationship of Earth and the sun. Polar ice is so
reflective that 90% of the sunlight that strikes it simply bounces back
into space, taking much of its energy with it. Ocean water does just
the opposite, absorbing 90% of the energy it receives. The more energy
it retains, the warmer it gets, with the result that each mile of ice
that melts vanishes faster than the mile that preceded it.

That is what scientists call a feedback loop, and it’s a nasty one,
since once you uncap the Arctic Ocean, you unleash another beast: the
comparatively warm layer of water about 600 ft. deep that circulates in
and out of the Atlantic. “Remove the ice,” says Woods Hole’s Curry,
“and the water starts talking to the atmosphere, releasing its heat.
This is not a good thing.”

A similar feedback loop is melting permafrost, usually defined as
land that has been continuously frozen for two years or more. There’s a
lot of earthly real estate that qualifies, and much of it has been
frozen much longer than two years–since the end of the last ice age,
or at least 8,000 years ago. Sealed inside that cryonic time capsule
are layers of partially decayed organic matter, rich in carbon. In
high-altitude regions of Alaska, Canada and Siberia, the soil is
warming and decomposing, releasing gases that will turn into methane
and CO2. That, in turn, could lead to more warming and permafrost thaw,
says research scientist David Lawrence of the National Center for
Atmospheric Research (NCAR) in Boulder, Colo. And how much carbon is
socked away in Arctic soils? Lawrence puts the figure at 200 gigatons
to 800 gigatons. The total human carbon output is only 7 gigatons a
year.

One result of all that is warmer oceans, and a result of warmer
oceans can be, paradoxically, colder continents within a hotter globe.
Ocean currents running between warm and cold regions serve as natural
thermoregulators, distributing heat from the equator toward the poles.
The Gulf Stream, carrying warmth up from the tropics, is what keeps
Europe’s climate relatively mild. Whenever Europe is cut off from the
Gulf Stream, temperatures plummet. At the end of the last ice age, the
warm current was temporarily blocked, and temperatures in Europe fell
as much as 10°F, locking the continent in glaciers.

What usually keeps the Gulf Stream running is that warm water is
lighter than cold water, so it floats on the surface. As it reaches
Europe and releases its heat, the current grows denser and sinks,
flowing back to the south and crossing under the northbound Gulf Stream
until it reaches the tropics and starts to warm again. The cycle works
splendidly, provided the water remains salty enough. But if it becomes
diluted by freshwater, the salt concentration drops, and the water gets
lighter, idling on top and stalling the current. Last December,
researchers associated with Britain’s National Oceanography Center
reported that one component of the system that drives the Gulf Stream
has slowed about 30% since 1957. It’s the increased release of Arctic
and Greenland meltwater that appears to be causing the problem,
introducing a gush of freshwater that’s overwhelming the natural cycle.
In a global-warming world, it’s unlikely that any amount of cooling
that resulted from this would be sufficient to support glaciers, but it
could make things awfully uncomfortable.

“The big worry is that the whole climate of Europe will change,”
says Adrian Luckman, senior lecturer in geography at the University of
Wales, Swansea. “We in the U.K. are on the same latitude as Alaska. The
reason we can live here is the Gulf Stream.”

DROUGHT

As fast as global warming is transforming the oceans and the ice
caps, it’s having an even more immediate effect on land. People,
animals and plants living in dry, mountainous regions like the western
U.S. make it through summer thanks to snowpack that collects on peaks
all winter and slowly melts off in warm months. Lately the early
arrival of spring and the unusually blistering summers have caused the
snowpack to melt too early, so that by the time it’s needed, it’s
largely gone. Climatologist Philip Mote of the University of Washington
has compared decades of snowpack levels in Washington, Oregon and
California and found that they are a fraction of what they were in the
1940s, and some snowpacks have vanished entirely.

Global warming is tipping other regions of the world into drought in
different ways. Higher temperatures bake moisture out of soil faster,
causing dry regions that live at the margins to cross the line into
full-blown crisis. Meanwhile, El Nino events–the warm pooling of
Pacific waters that periodically drives worldwide climate patterns and
has been occurring more frequently in global-warming years–further
inhibit precipitation in dry areas of Africa and East Asia. According
to a recent study by NCAR, the percentage of Earth’s surface suffering
drought has more than doubled since the 1970s.

FLORA AND FAUNA

Hot, dry land can be murder on flora and fauna, and both are taking
a bad hit. Wildfires in such regions as Indonesia, the western U.S. and
even inland Alaska have been increasing as timberlands and forest
floors grow more parched. The blazes create a feedback loop of their
own, pouring more carbon into the atmosphere and reducing the number of
trees, which inhale CO2 and release oxygen.

Those forests that don’t succumb to fire die in other, slower ways.
Connie Millar, a paleoecologist for the U.S. Forest Service, studies
the history of vegetation in the Sierra Nevada. Over the past 100
years, she has found, the forests have shifted their tree lines as much
as 100 ft. upslope, trying to escape the heat and drought of the
lowlands. Such slow-motion evacuation may seem like a sensible
strategy, but when you’re on a mountain, you can go only so far before
you run out of room. “Sometimes we say the trees are going to heaven
because they’re walking off the mountaintops,” Millar says.

Across North America, warming-related changes are mowing down other
flora too. Manzanita bushes in the West are dying back; some prickly
pear cacti have lost their signature green and are instead a sickly
pink; pine beetles in western Canada and the U.S. are chewing their way
through tens of millions of acres of forest, thanks to warmer winters.
The beetles may even breach the once insurmountable Rocky Mountain
divide, opening up a path into the rich timbering lands of the American
Southeast.

With habitats crashing, animals that live there are succumbing too.
Environmental groups can tick off scores of species that have been
determined to be at risk as a result of global warming. Last year,
researchers in Costa Rica announced that two-thirds of 110 species of
colorful harlequin frogs have vanished in the past 30 years, with the
severity of each season’s die-off following in lockstep with the
severity of that year’s warming.

In Alaska, salmon populations are at risk as melting permafrost
pours mud into rivers, burying the gravel the fish need for spawning.
Small animals such as bushy-tailed wood rats, alpine chipmunks and
pinon mice are being chased upslope by rising temperatures, following
the path of the fleeing trees. And with sea ice vanishing, polar
bears–prodigious swimmers but not inexhaustible ones–are starting to
turn up drowned. “There will be no polar ice by 2060,” says Larry
Schweiger, president of the National Wildlife Federation. “Somewhere
along that path, the polar bear drops out.”

WHAT ABOUT US?

It is fitting, perhaps, that as the species causing all the
problems, we’re suffering the destruction of our habitat too, and we
have experienced that loss in terrible ways. Ocean waters have warmed
by a full degree Fahrenheit since 1970, and warmer water is like rocket
fuel for typhoons and hurricanes. Two studies last year found that in
the past 35 years the number of Category 4 and 5 hurricanes worldwide
has doubled while the wind speed and duration of all hurricanes has
jumped 50%. Since atmospheric heat is not choosy about the water it
warms, tropical storms could start turning up in some decidedly
nontropical places. “There’s a school of thought that sea surface
temperatures are warming up toward Canada,” says Greg Holland, senior
scientist for NCAR in Boulder. “If so, you’re likely to get tropical
cyclones there, but we honestly don’t know.”

WHAT WE CAN DO

So much for environmental collapse happening in so many places at
once has at last awakened much of the world, particularly the 141
nations that have ratified the Kyoto treaty to reduce emissions–an
imperfect accord, to be sure, but an accord all the same. The U.S.,
however, which is home to less than 5% of Earth’s population but
produces 25% of CO2 emissions, remains intransigent. Many
environmentalists declared the Bush Administration hopeless from the
start, and while that may have been premature, it’s undeniable that the
White House’s environmental record–from the abandonment of Kyoto to
the President’s broken campaign pledge to control carbon output to the
relaxation of emission standards–has been dismal. George W. Bush’s
recent rhetorical nods to America’s oil addiction and his praise of
such alternative fuel sources as switchgrass have yet to be followed by
real initiatives.

The anger surrounding all that exploded recently when NASA
researcher Jim Hansen, director of the Goddard Institute for Space
Studies and a longtime leader in climate-change research, complained
that he had been harassed by White House appointees as he tried to
sound the global-warming alarm. “The way democracy is supposed to work,
the presumption is that the public is well informed,” he told TIME.
“They’re trying to deny the science.” Up against such resistance, many
environmental groups have resolved simply to wait out this
Administration and hope for something better in 2009.

The Republican-dominated Congress has not been much more
encouraging. Senators John McCain and Joe Lieberman have twice been
unable to get through the Senate even mild measures to limit carbon.
Senators Pete Domenici and Jeff Bingaman, both of New Mexico and both
ranking members of the chamber’s Energy Committee, have made global
warming a high-profile matter. A white paper issued in February will be
the subject of an investigatory Senate conference next week. A House
delegation recently traveled to Antarctica, Australia and New Zealand
to visit researchers studying climate change. “Of the 10 of us, only
three were believers,” says Representative Sherwood Boehlert of New
York. “Every one of the others said this opened their eyes.”

Boehlert himself has long fought the environmental fight, but if the
best that can be said for most lawmakers is that they are finally
recognizing the global-warming problem, there’s reason to wonder
whether they will have the courage to reverse it. Increasingly, state
and local governments are filling the void. The mayors of more than 200
cities have signed the U.S. Mayors Climate Protection Agreement,
pledging, among other things, that they will meet the Kyoto goal of
reducing greenhouse-gas emissions in their cities to 1990 levels by
2012. Nine eastern states have established the Regional Greenhouse Gas
Initiative for the purpose of developing a cap-and-trade program that
would set ceilings on industrial emissions and allow companies that
overperform to sell pollution credits to those that underperform– the
same smart, incentive-based strategy that got sulfur dioxide under
control and reduced acid rain. And California passed the nation’s
toughest automobile- emissions law last summer.

“There are a whole series of things that demonstrate that people
want to act and want their government to act,” says Fred Krupp,
president of Environmental Defense. Krupp and others believe that we
should probably accept that it’s too late to prevent CO2 concentrations
from climbing to 450 p.p.m. (or 70 p.p.m. higher than where they are
now). From there, however, we should be able to stabilize them and
start to dial them back down.

That goal should be attainable. Curbing global warming may be an
order of magnitude harder than, say, eradicating smallpox or putting a
man on the moon. But is it moral not to try? We did not so much march
toward the environmental precipice as drunkenly reel there, snapping at
the scientific scolds who told us we had a problem.

The scolds, however, knew what they were talking about. In a solar
system crowded with sister worlds that either emerged stillborn like
Mercury and Venus or died in infancy like Mars, we’re finally coming to
appreciate the knife-blade margins within which life can thrive. For
more than a century we’ve been monkeying with those margins. It’s long
past time we set them right.