T H E
G R E E N H O U S E E F F E C T
In
1827, a French scientist named Jean-Baptiste Joseph Fourier made a compelling
observation. He concluded that the Earth's atmosphere acts like an immense garden
greenhouse, trapping heat to warm the planet. (If he'd lived in the 20th Century
he might have called it the "Car Parked in the Open on a Sunny Day with its
Windows Rolled Up" but luckily he didn't!) He called the phenomenon "un effet
de verre," which means "an effect of glass." But the "greenhouse effect"
is an entirely natural phenomenon, and one which, on the whole and in the past,
has been very beneficial to humans and all life on our planet. Without it, temperatures
on Earth would be too cold. Here's how the greenhouse effect operates: Approximately
30 percent of the Sun's energy that reaches the Earth is reflected and scattered
by the surface and the atmosphere back into space.
The
remainder of this solar radiation is absorbed by the so-called "greenhouse
gases" in the atmosphere and the Earth's surface where it helps warm the
planet.
The
Earth radiates heat back out into the atmosphere. Much of the heat is absorbed
by greenhouse gases. As a result, the temperature of the Earth's surface and
the lower atmosphere stay warm enough for human life. The heat energy emitted
out to space prevents the planet from overheating.
Greenhouse Gases
Most greenhouse gases such as carbon dioxide, nitrous oxide,
and other trace gases like methane occur naturally. Water vapor in clouds is
also a contributor to the greenhouse effect but of course water is a molecule
of 2 hydrogen atoms and one oxygen, so it's not the same as the other "greenhouse
gases." Some are from natural emissions, and some are from human-induced emissions.
Without the greenhouse gases, Earth's climate would be about 60° Fahrenheit
colder than it is today.
The
greenhouse effect thus serves an essential function, but human activities may
intensify this natural phenomenon. An international group of the world's leading
climate researchers (the Intergovernmental Panel on Global Climate Change) is
now convinced that global climate change is definitely occurring, as seen in
rising temperatures and increasing amounts of carbon dioxide in the atmosphere.
It is still unclear, however, how much of this is natural and how much human
induced.
But
we do know that our activities can increase the concentration of greenhouse
gases in the atmosphere. Burning fossil fuels to power our cars, homes, and
factories releases carbon dioxide and increases concentrations of other greenhouse
gases like methane and nitrous oxide. Humans even manufacture some greenhouse
gases, with complicated names such as chlorofluorocarbons (CFCs), hydrofluorocarbons,
perfluorocarbons, and sulfur hexafluoride. Many of these gases can remain in
the atmosphere for decades or even centuries. The concern is that at a certain,
as yet unknown level, the greenhouse gases may begin to trigger very unwelcome
and perhaps irreversible effects. Planetary scientists look at Venus, with temperatures
on its surface hot enough to melt lead, and talk about the "runaway greenhouse
effect" that makes that planet completely uninhabitable.
CFCs
have been linked to the reduction of Earth's ozone layer,which is essential
in protecting life on the surface of our planet, and in the upper layers of
the ocean, from ultraviolet (UV) radiation.
An
unprecedented series of international conventions has reduced the rate of emission
of CFCs into the atmosphere considerably. Many climate researchers think that
we should control such emissions as a kind of "global insurance policy" in case,
some decades from now, we find out that, without a doubt, we humans are indeed
making our planet’s climate and weather very different from the past.
(Adapted, with
permission, from the ERA/NASA/NOAA
Climate Change Presentation Kit CD-ROM.)
Images provided
by the Atmospheric Chemistry
& Dynamic Branch of NASA
