http://magma.nationalgeographic.com/ngm/0409/feature1/

There's no question that the Earth is getting hotter--and fast. The
real questions a How much of the warming is our fault, and are we
willing to slow the meltdown by curbing our insatiable appetite for
fossil fuels?

Get a taste of what awaits you in print from this compelling excerpt.

Global warming can seem too remote to worry about, or too
uncertain--something projected by the same computer techniques that
often can't get next week's weather right. On a raw winter day you
might think that a few degrees of warming wouldn't be such a bad thing
anyway. And no doubt about it: Warnings about climate change can sound
like an environmentalist scare tactic, meant to force us out of our
cars and cramp our lifestyles.

Comforting thoughts, perhaps. But turn to "GeoSigns," the first
chapter in our report on the changing planet. The Earth has some
unsettling news.

From Alaska to the snowy peaks of the Andes the world is heating up
right now, and fast. Globally, the temperature is up 1°F (-17°C) over
the past century, but some of the coldest, most remote spots have
warmed much more. The results aren't pretty. Ice is melting, rivers
are running dry, and coasts are eroding, threatening communities.
Flora and fauna are feeling the heat too, as you'll read in
"EcoSigns." These aren't projections; they are facts on the ground.

The changes are happening largely out of sight. But they shouldn't be
out of mind, because they are omens of what's in store for the rest of
the planet.

Wait a minute, some doubters say. Climate is notoriously fickle. A
thousand years ago Europe was balmy and wine grapes grew in England;
by 400 years ago the climate had turned chilly and the Thames froze
repeatedly. Maybe the current warming is another natural vagary, just
a passing thing?

Don't bet on it, say climate experts. Sure, the natural rhythms of
climate might explain a few of the warming signs you'll read about in
the following pages. But something else is driving the planet-wide
fever.

For centuries we've been clearing forests and burning coal, oil, and
gas, pouring carbon dioxide and other heat-trapping gases into the
atmosphere faster than plants and oceans can soak them up (see "The
Case of the Missing Carbon," February 2004). The atmosphere's level of
carbon dioxide now is higher than it has been for hundreds of
thousands of years. "We're now geological agents, capable of affecting
the processes that determine climate," says George Philander, a
climate expert at Princeton University. In effect, we're piling extra
blankets on our planet.

Human activity almost certainly drove most of the past century's
warming, a landmark report from the United Nations Intergovernmental
Panel on Climate Change (IPCC) declared in 2001. Global temperatures
are shooting up faster than at any other time in the past thousand
years. And climate models show that natural forces, such as volcanic
eruptions and the slow flickers of the sun, can't explain all that
warming.

As carbon dioxide continues to rise, so will the mercury--another 3°F
to 10°F (-16°C to -12°C) by the end of the century, the IPCC projects.
But the warming may not be gradual. The records of ancient climate
described in "TimeSigns" suggest that the planet has a sticky
thermostat. Some experts fear today's temperature rise could
accelerate into a devastating climate lurch. Continuing to fiddle with
the global thermostat, says Philander, "is just not a wise thing to
do."

Get the whole story in the pages of National Geographic magazine.