Global Warming (página 2)

Have
you ever seen a greenhouse? Most greenhouses look like a small
glass house. Greenhouses are used to grow plants, especially in
the winter. Greenhouses work by trapping heat from the sun. The
glass panels of the greenhouse let in light but keep heat from
escaping. This causes the greenhouse to heat up, much like the
inside of a car parked in sunlight, and keeps the plants warm
enough to live in the winter.

The Earth"s atmosphere is all around us. It is the air that we
breathe. Greenhouse gases in the
atmosphere behave much like the glass panes in a greenhouse.
Sunlight enters the Earth's atmosphere, passing through the
blanket of greenhouse gases. As it reaches the Earth's surface,
land, water, and
absorb the sunlight"s energy. Once absorbed, this energy is sent
back into the atmosphere. Some of the energy passes back into
space, but much of it remains trapped in the atmosphere by the
greenhouse gases, causing our world to heat up.

The greenhouse effect is important. Without the greenhouse
effect, the Earth would not be warm enough for humans to live.
But if the greenhouse effect becomes stronger, it could make the
Earth warmer than usual. Even a little extra warming may cause
problems for humans, plants, and animals.

What is the climate
system?

It may seem hard to believe that people can actually change
the Earth"s climate.
But scientists think that the things people do that send greenhouse
gases into the air are making our planet warmer.

Atmosphere
The atmosphere covers the Earth. It is a thin layer of mixed
gases which make up the air we breathe. This thin layer also
helps the Earth from becoming too hot or too cold, much like
clothing does for us. Weather
systems, which develop in the lower atmosphere, are driven by
heat from the sun, the rotation of the Earth, and variations in
the Earth's surface.

Oceans
Oceans cover about 70 percent of Earth's surface. Their large
mass and thermal
properties enable them to store vast quantities of heat. Oceans
buffer and regulate temperature – energy absorbed or lost by the
oceans results in a smaller surface temperature change than would
occur over land. The atmosphere and ocean constantly exchange
energy and matter. For example, water evaporates from the oceans
into the atmosphere. This moisture then falls back to the Earth
as precipitation
– rain, snow, sleet, and even the morning dew on the grass.

Land
Land covers 27 percent of Earth's surface, and land topography
influences weather patterns. For example, the weather in areas
covered by mountains can be completely different than the weather
in areas where the land is mostly flat.

Ice
Ice
is the world's largest supply of freshwater. It covers the
remaining 3 percent of Earth's surface including most of
Antarctica and Greenland. Because ice is highly reflective and
because of its insulating properties, ice plays an important role
in regulating climate.

Biosphere
The biosphere is that part of Earth's atmosphere, land,
oceans that supports any living plant, animal, or organism. It is
the place where plants and animals, including humans, live. Large
quantities of carbon dioxide are exchanged between the land-based
biosphere and the atmosphere as plants take in carbon dioxide and
give off oxygen, and animals inhale oxygen and exhale carbon
dioxide.

Climate"s come a long
way!

Earth's climate has been changing constantly over its
5-billion-year history. Sometimes, the climate has warmed so that
the oceans have risen and covered much of the Earth. Each of the
changes may seem extreme, but they usually occurred slowly over
many thousands of years.

Ancient Climate History
The first
people arrived in America between 15,000 and 30,000 years ago.
During that time, much of North America was covered by great ice
sheets. Some 14,000 years ago, the last ice sheet began to melt
very quickly. By 7,000 years ago, the ice was gone.

This end to
the ice ages caused big changes on the Earth. The changes caused
many kinds of plants and animals to die. For example, mastodons –
elephant-like animals – and other large mammals that preferred
cold climates may not have been able to live in the warmer, drier
conditions.

The Little Ice Age
Starting in the 14th century, Europeans lived
through what is known as the "Little Ice Age." The Little Ice Age
lasted for several hundred years. During the Little Ice Age, the
advance of glaciers along with hard winters and famines caused
some people to starve and others to leave their homes.

Recent Climate
History
The Earth
has warmed about 1ºF in
the last 100 years. The eight warmest years on record (since
1850) have all occurred since 1998, with the warmest year being
2005. Periods of increased heat from the sun may have helped make
the Earth warmer. But many of the world's leading climatologists
think that the greenhouse
gases people produce are making the Earth warmer, too.

Melting
Glaciers: a glacier is a large sheet of ice that moves very,
very slowly. Many glaciers in the world are now melting. For
example, glaciers are melting in Montana's Glacier National Park.
Some scientists think the glaciers are melting partly because the
Earth is getting warmer.

Rising
Sea Level: have you ever built a sandcastle on the beach,
close to the ocean on wet sand? If you have, you probably know
that the sandcastle won't last very long. Chances are the waves
will wash away the sandcastle as soon as the tide comes in. The
water goes higher up the beach when the tide comes in. At most
shores throughout the world, two high tides and two low tides
occur every day. But now the level of the sea is rising, so high
tides are higher than they were before. Over the last 100 years,
the level of the sea has risen about 6-8 inches worldwide. When
the sea level rises, the tide goes farther up the beach.

Scientists
think the sea has risen partly because of melting glaciers and
sea ice. When some glaciers melt, they release water into the sea
and make it higher than it was before. Scientists also think that
warmer temperatures in the sea make it rise even more. Heat makes
water expand. When the ocean expands, it takes up more space.

What might happen?

Scientists
are not fortune-tellers. They don't know exactly what will happen
in the future. But they can use special computer programs to find
out how the climate may change in the years ahead. And the
computer programs tell us that the Earth may continue to get
warmer.

Together,
the melting glaciers, rising seas, and computer models provide
some good clues. They tell us that the Earth's temperature will
probably continue to rise as long as we continue increasing the
amount of greenhouse gases in the atmosphere.

Can we change the
climate?

It may seem hard to believe that people can actually change
the Earth"s climate. But
scientists think that the things people do that send greenhouse
gases into the air are making our planet warmer.

Once, all
climate changes occurred naturally. However, during the Industrial
Revolution, we began altering our climate and environment
through agricultural and industrial
practices. The Industrial Revolution was a time when people began
using machines to make life easier. It started more than 200
years ago and changed the way humans live. Before the Industrial
Revolution, human activity released very few gases into the
atmosphere, but now through population growth, fossil fuel
burning, and deforestation,
we are affecting the mixture of gases in the atmosphere.

Since the Industrial Revolution, the need for energy to run
machines has steadily increased. Some energy, like the energy you
need to do your homework, comes from the food you eat. But other
energy, like the energy that makes cars run and much of the
energy used to light and heat our homes, comes from fuels like
coal and oil – fossil fuels. Burning these fuels releases
greenhouse gases.

When do you send greenhouse
gases into the air?

Whenever you…

… you are helping to send greenhouse gas into the
air.

To perform many of these functions, you need to use
electricity. Electricity comes from power plants. Most power
plants use coal and oil to make electricity. Burning coal and oil
produces greenhouse gases.

Other things we do send greenhouse gases into the air too;

The
trash that we send to landfills produces a greenhouse gas called
methane.
Methane is also produced by the animals we raise for dairy and
meat products and when we take coal out of the ground. Whenever
we drive or ride in a car, we are adding greenhouse gases to the
atmosphere. And, when factories make the things that we buy and
use everyday, they too are sending greenhouse gases into the
air.

So… What"s the big
deal?

Sometimes little things can turn into big things. Think about
brushing your teeth. If you don't brush for one day, chances are
nothing bad will happen. But if you don't brush your teeth for
one month, you may develop a cavity. It's the same thing with
global temperatures. If temperatures rise above normal levels for
a few days, it's no big deal – the Earth will stay more or less
the same. But if temperatures continue to rise over a longer
period of time, then the Earth may experience some problems.

Average global
temperature has increased by almost 1ºF over
the past century; scientists expect the average global
temperature to increase an additional 2 to 6ºF over the next
one hundred years. This may not sound like much, but it could
change the Earth's climate as
never before. At the peak of the last ice age (18,000 years ago),
the temperature was only 7ºF colder than it is today, and
glaciers
covered much of North America!

Even
a small increase in temperature over a long time can change the
climate. When the climate changes, there may be big changes in
the things that people depend on. These things include the level
of the oceans and the places where we plant crops. They also
include the air we breathe and the water we drink.

What
Might Happen? It is important to understand that scientists don't
know for sure what climate change will bring. Some changes
brought about by climate change will be good. If you live in a
very cool climate, warmer temperatures might be welcome. Days and
nights could be more comfortable and people in the area may be
able to grow different and better crops than they could before.
But it is also true that changes in some places will not be very
good at all.

Human Health

Climate change may affect people's health both directly and
indirectly. For example, heat stress
and other heat related health problems are caused directly by
very warm temperatures and high humidity. Untreated, heat
stress can be
a very serious medical problem. Scientists suspect that, in many
places, climate change will increase the number of very hot days
that occur during the year. More hot days increases the
possibility of heat related health problems.

Indirectly, ecological
disturbances, air pollution, changes in food and water
supplies, and coastal flooding are all examples of possible
impacts that might affect human health.

How
people and nature adapt to climate change will determine how
seriously it impacts human health. Some people and places are
likely to be affected more than others. Generally, poor people
and poor countries are less likely to have the money and
resources they need to cope with preventing and treating health
problems. Very young children and the elderly adults will run the
highest risks.

Ecological Systems

Climate change may alter the world's habitats and
ecosystems –
all living things are included in and rely on these places. Many
of these places depend on a delicate balance of rainfall,
temperature, and soil type. A rapid change in climate could upset
this balance and seriously endanger many living things.

Most
past climate changes occurred slowly, allowing plants and animals
to adapt to the new environment
or move somewhere else. However, if future climate changes occur
as rapidly as some scientists predict, plants and animals may not
be able to react quickly enough to survive. The ocean's
ecosystems also could be affected for the same reasons.

Sea Level Rise

Global warming may make the sea level become higher. Why?
Well, warmer weather
makes glaciers melt. A glacier is a large sheet of ice that moves
very, very slowly. Some melting glaciers add more water to the
ocean. Warmer temperatures also make water expand. When water
expands in the ocean, it takes up more space and the level of the
sea rises.

  Sea
level may rise between several inches and as much as 3 feet
during the next century. This will affect both natural systems
and manmade structures along coastlines. Coastal flooding could
cause saltwater to flow into areas where salt is harmful,
threatening plants and animals in those areas. For example, an
increase in the salt content of the Delaware and Chesapeake bays
is thought to have decreased the number of oysters able to live
in those waters.

Oceanfront property would be affected by flooding, and beach
erosion could leave structures even more vulnerable to storm
waves. Whether we move back from the water or build barricades
in the face of a rising sea, it could cost billions of dollars to
adapt to such change. Coastal flooding also may reduce the
quality of drinking water in coastal areas.

Crops and Food Supply

Global warming may make the Earth warmer in cold places.
People living in these places may have a chance to grow crops in
new areas. But climate change also might bring droughts to
other places where we grow crops. In some parts of the world,
people may not have enough to eat because they cannot grow the
food that they need.

We can make a
difference!

Climate change may be a big problem, but there are many little
things we can do to make a difference. If we try, most of us can
do our part to reduce the amount of greenhouse
gases that we put into the atmosphere. Many greenhouse gases
come from things we do every day. As we have learned, these
greenhouse gases trap energy in the atmosphere and make the Earth
warmer.

Driving a car or using electricity is not wrong. We just have
to be smart about it. Some people use less energy by carpooling.
For example, four people can ride together in one car instead of
driving four cars to work. Here are some additional ways you can
help make the planet a better place!

Read
Learning about the environment
is very important. There are many good books that will help you
learn. To get started, ask a teacher or a librarian for some
suggestions. You also can look at the Links page to find other
good web sites with
information about the environment and climate
change.

Save Electricity
Whenever we use electricity, we help put greenhouse gases
into the air. By turning off lights, the television, and the
computer when you are through with them, you can help a lot.

Bike, Bus, and
Walk
You
can save energy by sometimes taking the bus, riding a bike, or
walking.

Talk to Your Family and Friends
Talk with your family and friends about
climate change. Let them know what you've learned.

Plant Trees
Planting trees is fun and a great way to reduce greenhouse
gases. Trees absorb carbon dioxide, a greenhouse gas, from the
air.

Recycle
Recycle cans, bottles, plastic bags, and newspapers. When you
recycle, you send less trash to the landfill and you help save
natural resources, like trees, oil, and elements such as
aluminum.

When You Buy, Buy Cool Stuff
There are lots of ways we can improve the
environment. One of the ways to reduce the amount of greenhouse
gases that we put into the air is to buy products that don't use
as much energy. By conserving energy, we help reduce climate
change and make the Earth a better place. Some products – like
certain cars and stereos – are made specially to save energy.

Some Things to Think About
Did you know that you can help the environment if
you buy recyclable products instead of non-recyclable ones? Look
for the recycle mark – three arrows that make a circle – on the
package. Recyclable products are usually made out of things that
already have been used. It usually takes less energy to make
recycled products than to make new ones. The less energy we use,
the better.

Solar Energy
Imagine that it's a hot summer day. You put a scoop of ice
cream on the sidewalk, and it melts. Why? Well, you probably know
that the sun causes the ice cream to melt. But you may not know
that the sun produces solar
energy. Solar energy is a fancy way of saying "energy that
comes from the sun." Solar energy can be used to heat homes,
buildings, water, and to make electricity. Today, more than
200,000 houses in the United States take advantage of the sun's
energy.

Cars
Cars
are an important part of life for most people. But cars also
cause pollution and release a lot of greenhouse gases into the
air. Fortunately, there are some cars that are better for the
environment. These cars can travel longer on a smaller amount of
gasoline. They don't pollute as much, either. Using these kinds
of cars can help reduce the amount of greenhouse gases in the
air.

ENERGY STAR®

Many
things, like computers, TVs, stereos, and VCRs, have special
labels on them. The label says "Energy" and has a picture of a
star. Products with the ENERGY STAR® label are
made to save energy. Buying products with ENERGY
STAR® labels will help protect the
environment.

Autora:

Analía Massa

Argentina

18/10/2008