How do scientists know that global temperature has been
rising for the past several centuries?
Actual temperature records dating back about 250 years for
many spots on Earth show a general trend upward. The temperature—averaged
across all locations over many years—shows an increase,
even though each individual location has not warmed. And even
though actual temperature readings were scarce before the
1700s, nature has a way of preserving temperature records
in the bodies of living things. Trees, for example, tend to
grow faster in warmer weather. By looking at the growth rings
for different species
over time, scientists can estimate which years were cooler
or warmer.
Another example comes from the ocean, where tiny, shelled
creatures called "forams" live. These creatures take oxygen
out of the seawater and combine it with calcium
and carbon to make their shells. How can the oxygen in these
shells tell us about Earth's temperatures long ago? Even though
oxygen seems all the same to us, it has several different
forms, or "isotopes." Normal oxygen is called oxygen 16, but
there is a heavier isotope called oxygen 18. More 18O in seawater
indicates more glacier ice in the world (and, therefore, a
colder global climate). By comparing the ratio of 18O to 16O
in the seashells of creatures who lived hundreds or even thousands
of years ago, scientists can tell how Earth's surface temperature
has changed.
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How does a greenhouse trap heat?
Visible light is part of a broad band of radiation called
the "electromagnetic
spectrum." Visible light can easily pass through the glass
of a greenhouse, but when it strikes soil, plants, water,
and the ground, some of the light is absorbed and changed
to a different type of radiation called infrared. You can't
see infrared energy, but you can feel it—it's also known
as heat! Although visible light can easily pass through glass,
infrared radiation gets blocked by it. As a result, the heat
gets trapped inside the greenhouse, and, as long as new light
keeps shining in, the temperature keeps rising. This is why
on a bright, sunny day, the temperature inside a greenhouse
can get close to 100 degrees F even when the temperature outside
is freezing.
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Why do concrete and asphalt create an "urban heat island"?
Concrete and asphalt create an urban
heat island because of several factors:
- They conduct heat energy better than grass, trees and
water do. When sunlight shines on asphalt and concrete roads,
parking lots, and sidewalks, much of the visible light is
absorbed and changed to infrared or heat energy. (This is
especially true of the dark-colored asphalt, which absorbs
heat better then light-colored materials do.)
- Because buildings and roads are massive, they can store
heat for a long time, even after it gets dark.
- Not only do the leaves of plants and trees help to shade
the underlying ground from direct sunlight, but they also
"transpire"
(give off) water vapor, which cools the air around them.
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How can forests help prevent droughts?
Trees help "buffer" moisture conditions in the atmosphere
and safeguard against droughts in a number of important ways.
- Their leaves help shade the ground below, reducing the
overall temperature and slowing the rate of moisture evaporation
from the surrounding soil.
- Leaf litter on the ground and tree roots slow the rate
of runoff from the land surface after it rains, giving the
water more of a chance to seep into the ground and "recharge"
the ground water system.
- When trees grow, they transpire, releasing moisture into
the air, which not only cools the atmosphere but also provides
a source of new rainwater when it condenses back into clouds.
- Tree roots tap into moisture found deep in the soil, which
helps to add more water to the local cycle.
- Tree roots also hold the soil in place, keeping it from
eroding away and becoming compacted. Once soil has been
damaged, it cannot hold moisture and tends to dry out faster,
making drought conditions worse.
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What can a person do to avoid getting a vector-borne disease?
Most vector-borne
diseases are carried by blood-sucking arthropods such as ticks,
fleas, and mosquitoes. The easiest way to protect yourself
from getting the diseases that these creatures carry is by
preventing them from biting you in the first place. Wearing
long pants and shirts when you go into wooded and grassy areas
helps. So does wearing insect repellent. Reduce breeding grounds
for mosquitoes by making sure that there are no stagnant pools
of water near where you live. Remove or empty tires, garden
pots or any outdoor containers. It's a good idea to try to
eliminate rats and mice, which often play host to the fleas
and ticks that carry the diseases.
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Doesn't adding chlorine to water kill disease-causing
organisms?
While it is true that chlorine kills many disease-causing
organisms found in drinking water, it does not kill all of
them. The parasite
that causes cryptosporidiosis
("crypto" for short), for example, is extremely resistant
to chlorine and is sometimes found living in public water
supply systems even after the water has been treated with
chemicals.
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Do all water filters remove disease-causing organisms
from drinking water?
The answer is a resounding no! In order to be effective
against many disease-causing organisms, including cryptosporidiosis,
a filter must be extremely fine. The openings have to be 1
micron (that's 1 millionth of a meter) or smaller. When purchasing
filters for your home, read the package carefully. It will
usually tell you which diseases it protects against.
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What's the most effective way to treat drinking water
if you think it's been contaminated?
High-grade filters and chemical water treatment kits sold
for hikers and campers are effective against most contaminants,
but the only sure way to kill off all the living parasites
found in drinking water is to boil the water for at least
five minutes before drinking it. It is important to note that
although boiling kills germs, it does nothing to remove chemical
contaminants that may be in the water. The only way to remove
them is by distilling the water.
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Doesn't using anti-bacterial soap and detergent kill
germs found in water?
Anti-bacterial soap kills some bacteria,
but it does very little to stop the spread of viruses and
other microbes, especially if these "germs" are found in the
water you are washing with. Washing your hands or food in
water contaminated with parasites
such as "crypto" can actually help spread them to your food.
It is also important to note that because of the excessive
use of antibiotics,
many strains of bacteria have become resistant to standard
anti-bacterial soap.
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How can eating fish give you cholera?
Scientists now know that the bacteria
that cause the disease cholera
can live inside a tiny creature called a copepod.
These marine invertebrates
are especially plentiful in warm coastal waters, where fresh
water from streams and rivers mixes with ocean water. Copepods
and other forms of "zooplankton" are the main food source
for small fish, crustaceans (such as crabs and shrimp), and
especially shellfish (such as clams, mussels and oysters,
which filter them out of the water. By eating raw or undercooked
fish and shellfish that have eaten these copepods, you may
also be eating the cholera bacteria that they carried. Making
sure that all fish is well cooked is the best way to safeguard
against getting the disease in the first place. Cooking at
a high temperature usually kills the cholera bacteria.
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How can you avoid getting cholera from drinking water?
The easiest way of safeguarding your drinking water if you
are in an area where there is a cholera outbreak: Boil the
water for five minutes before drinking it. Boiling water kills
the cholera bacteria. Most sanitation systems that use chlorination
to kill bacteria are quite effective in eliminating cholera.
Although not completely safe, when infection levels are high
and no other methods are available, filtering water through
sari cloth (as is done in parts of Bangladesh) can reduce
the transmission of cholera.
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Can you get water-borne diseases from recreational water?
Absolutely! Swimming or bathing in water contaminated with
bacteria or disease-causing parasites can have the same negative
effects as drinking the water. Disease-causing organisms can
enter the body through cuts in the skin, and even through
your eyes and nose. In addition, if you accidentally swallow
any water while swimming, it's as bad as drinking it.
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Is the melting of glaciers the only thing responsible
for the rising sea level?
Only a small part of sea-level rise is a result of melting
glaciers and polar ice caps. A far more significant problem
is caused by "thermal expansion" of the water itself as it
gets warmer. Most forms of matter (solids, liquids and gases)
expand or get bigger as they heat up—and seawater is
no exception. Because the volume of the ocean is so enormous,
even a small rise in temperature results in a measurable rise
in sea level.
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Could global warming affect our food supply?
Yes, in surprising ways that no one can anticipate. For example, the Gulf Stream, a powerful ocean current that runs from the southeastern U.S. to northern Europe, keeps huge areas of Europe warm enough to support agriculture. Melting ice in the north Atlantic could cool the Gulf Stream, which would, in turn, bring colder weather to much of Europe. While this would not occur overnight, it is possible. Indeed, fossil evidence indicates that it may have happened several times in the past.
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How can you "desalinate" water once it's been contaminated
with salt?
Though bacteria
and other "living" contaminants can be filtered from water
fairly easily, it's extremely difficult to filter the salt
from water. That's because once the salt dissolves in water,
it goes into solution (changing the actual substance, so there's
no going back). The most effective way of getting the salt
out is to distill the water, which means evaporating the liquid,
capturing the vapor and then recondensing the vapor back into
liquid water again. When the water turns into a vapor, the
salt is left behind. In order to evaporate large quantities
of water, you need to heat it to high temperatures, which
requires a great deal of energy. In some areas, water is distilled
using solar stills, which get their energy directly from the
sun. Stills that get energy from fossil fuels are expensive
to operate and add new greenhouse gases to the air.
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How does turning off a light help reduce global warming?
Most of the electricity used for running computers, lights,
television sets, and video game systems is generated by power
plants that burn fossil fuels to make steam to turn a turbine
that spins a generator. Since the burning of fossil
fuels adds greenhouse
gases to the air, any reduction in their use will help
turn the problem around. The bottom line is that the less
electricity we use, the less we need to burn fossil fuels.
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