Rambler's Top100





7
What Is Global Warming?
Glaciers are melting, sea levels are rising and wildlife is scrambling to
keep pace. It's becoming clear that humans have caused most of the past cen-
tury's warming by releasing heat-trapping gases as we power our modern
lives. Called greenhouse gases (GHGs), their levels are higher now than in
the last 650,000 years.
SEE HOW IT WORKS
We call the result global warming, but it is causing a set of changes to
the Earth's climate, or long-term weather patterns, that varies from place to
place. As the Earth spins each day, the new heat swirls with it, picking up
moisture over the oceans, rising here, settling there. It's changing the rhythms
of climate that all living things have come to rely upon. What will we do to
slow this warming? How will we cope with the changes we've already set
into motion?
GREENHOUSE EFFECT
The "greenhouse effect" is the warming that happens when certain gases
in Earth's atmosphere trap heat. These gases let in light but keep heat from
escaping, like the glass walls of a greenhouse.
First, sunlight shines onto the Earth's surface, where it is absorbed and
then radiates back into the atmosphere as heat. In the atmosphere, ―green-
house‖ gases trap some of this heat, and the rest escapes into space. The more
greenhouse gases are in the atmosphere, the more heat gets trapped.
Scientists have known about the greenhouse effect since 1824, when Jo-
seph Fourier calculated that the Earth would be much colder if it had no at-
mosphere. This greenhouse effect is what keeps the Earth's climate livable.
Without it, the Earth's surface would be an average of about 60 degrees Fa-
hrenheit cooler. In 1895, the Swedish chemist Svante Arrhenius discovered
that humans could enhance the greenhouse effect by making carbon dioxide,
a greenhouse gas.
Levels of greenhouse gases (GHGs) have gone up and down over the
Earth's history, but they have been fairly constant for the past few thousand
years. Global average temperatures have stayed fairly constant over that time
as well, until recently. Through the burning of fossil fuels and other GHG
emissions, humans are enhancing the greenhouse effect and warming Earth.
Other factors briefly influence global temperatures. Volcanic eruptions, for
example, emit particles that temporarily cool the Earth's surface. But these
have no lasting effect beyond a few years. Now, humans have increased the
amount of carbon dioxide in the atmosphere by more than a third since the
industrial revolution.