This document discusses the causes and impacts of global warming. It begins by explaining that while Earth's climate has naturally varied in the past due to factors like orbital shifts and solar activity, the dominant influence now is human activity. It then describes the natural greenhouse effect and how greenhouse gases like carbon dioxide trap heat in the lower atmosphere, making the planet warmer than it would otherwise be. However, the warming seen recently cannot be explained by natural causes alone. Human emissions of greenhouse gases, which far exceed levels from other sources like volcanoes, are the main driver of current warming according to scientists. The impacts of continued warming will include changes to weather patterns, rising sea levels, pressure on ecosystems, and effects on human communities and activities.

1. GLOBALWARMING
Throughout its long history, Earth has warmed and
cooled time and again. Climate has changed when the planet received more or
less sunlight due to subtle shifts in its orbit, as the atmosphere or surface
changed, or when the Sun’s energy varied. But in the past century, another force
has started to influence Earth’s climate: humanity
How does this warming compare to previous changes in Earth’s climate? How
can we be certain that human-released greenhouse gases are causing the
warming? How much more will the Earth warm? How will Earth respond?
Answering these questions is perhaps the most significant scientific challenge of
our time.
EARTH’S NATURAL GREENHOUSEEFFECT
Earth’s temperature begins with the Sun. Roughly
30 percent of incoming sunlight is reflected back into space by bright surfaces
like clouds and ice. Of the remaining 70 percent, most is absorbed by the land
and ocean, and the rest is absorbed by the atmosphere. The absorbed solar
energy heats our planet.
As the rocks, the air, and the seas warm, they radiate “heat” energy (thermal
infrared radiation). From the surface, this energy travels into the atmosphere

2. where much of it is absorbed by water vapor and long-lived greenhouse gases
such as carbon dioxide and methane.
When they absorb the energy radiating from Earth’s surface, microscopic water
or greenhouse gas molecules turn into tiny heaters— like the bricks in a
fireplace, they radiate heat even after the fire goes out. They radiate in all
directions. The energy that radiates back toward Earth heats both the lower
atmosphere and the surface, enhancing the heating they get from direct sunlight.
This absorption and radiation of heat by the atmosphere—the natural
greenhouse effect—is beneficial for life on Earth. If there were no greenhouse
effect, the Earth’s average surface temperature would be a very chilly -18°C
(0°F) instead of the comfortable 15°C (59°F) that it is today.
IS CURRENTWARMING NATURAL?
In Earth’s history before the Industrial Revolution,
Earth’s climate changed due to natural causes not related to human activity.
Most often, global climate has changed because of variations in sunlight. Tiny
wobbles in Earth’s orbit altered when and where sunlight falls on Earth’s
surface. Variations in the Sun itself have alternately increased and decreased the
amount of solar energy reaching Earth. Volcanic eruptions have generated
particles that reflect sunlight, brightening the planet and cooling the climate.
Volcanic activity has also, in the deep past, increased greenhouse gases over
millions of years, contributing to episodes of global warming.
Although volcanoes are active around the world, and
continue to emit carbon dioxide as they did in the past, the amount of carbon
dioxide they release is extremely small compared to human emissions. On
average, volcanoes emit between 130 and 230 million tonnes of carbon dioxide
per year. By burning fossil fuels, people release in excess of 100 times more,
about 26 billion tonnes of carbon dioxide, into the atmosphere every year (as of

3. 2005). As a result, human activity overshadows any contribution volcanoes may
have made to recent global warming.
Changes in the brightness of the Sun can influence the climate from decade to
decade, but an increase in solar output falls short as an explanation for recent
warming. NASA satellites have been measuring the Sun’s output since 1978.
The total energy the Sun radiates varies over an 11-year cycle. During solar
maxima, solar energy is approximately 0.1 percent higher on average than it is
during solar minimum.
HOW WILL GLOBAL WARMING CHANGE EARTH?
The impact of increased surface temperatures
is significant in itself. But global warming will have additional, far-reaching
effects on the planet. Warming modifies rainfall patterns, amplifies coastal
erosion, lengthens the growing season in some regions, melts ice caps and
glaciers, and alters the ranges of some infectious diseases. Some of these
changes are already occurring.
Global warming will shift major climate patterns, possibly prolonging and intensifying the current
drought in the U.S. Southwest. The white ring of bleached rock on the once-red cliffs that hold Lake
Powell indicate the drop in water level over the past decade—the result of repeated winters with low
snowfall. (Photograph ©2006Tigresblanco.)
1. CHANGING WEATHER
For most places, global warming will result in more
frequent hot days and fewer cool days, with the greatest warming occurring over
land. Longer, more intense heat waves will become more common. Storms,
floods, and droughts will generally be more severe as precipitation patterns
change. Hurricanes may increase in intensity due to warmer ocean surface
temperatures.

4. It is impossible to pin any single unusual weather event
on global warming, but emerging evidence suggests that global warming is
already influencing the weather. Heat waves, droughts, and intense rain events
have increased in frequency during the last 50 years, and human-induced global
warming more likely than not contributed to the trend.
2. RISING SEA LEVELS
The weather isn’t the only thing global warming will
impact: rising sea levels will erode coasts and cause more frequent coastal
flooding. Some island nations will disappear. The problem is serious becauseup
to 10 percent of the world’s population lives in vulnerable areas less than 10
meters (about 30 feet) above sea level.
The Intergovernmental Panel on Climate Change (IPCC)
estimates that sea levels will rise between 0.18 and 0.59 meters (0.59 to 1.9 feet)
by 2099 as warming sea water expands, and mountain and polar glaciers melt.
These sea level change predictions may be underestimates, however, because
they do not account for any increases in the rate at which the world’s major ice
sheets are melting. As temperatures rise, ice will melt more quickly. Satellite
measurements reveal that the Greenland and West Antarctic ice sheets are
shedding about 125 billion tons of ice per year - enough to raise sea levels by
0.35 millimeters (0.01 inches) per year. If the melting accelerates, the increase
in sea level could be significantly higher.
3. IMPACTING ECOSYSTEMS
More importantly, perhaps, global warming is
already putting pressure on ecosystems, the plants and animals that co-exist in a
particular climate zone, both on land and in the ocean. Warmer temperatures
have already shifted the growing season in many parts of the globe. The
growing season in parts of the Northern Hemisphere became two weeks longer
in the second half of the 20th century. Spring is coming earlier in both
hemispheres.
This change in the growing season affects the
broader ecosystem. Migrating animals have to start seeking food sources earlier.
The shift in seasons may already be causing the lifecycles of pollinators, like
bees, to be out of synch with flowering plants and trees. This mismatch can
limit the ability of both pollinators and plants to survive and reproduce, which
would reduce food availability throughout the food chain.
See Buzzing about Climate Change to read more about how the lifecycle of bees
is synched with flowering plants.
Warmer temperatures also extend the growing
season. This means that plants need more water to keep growing throughout the

5. season or they will dry out, increasing the risk of failed crops and wildfires.
Once the growing season ends, shorter, milder winters fail to kill dormant
insects, increasing the risk of large, damaging infestations in subsequent
seasons.
In some ecosystems, maximum daily temperatures
might climb beyond the tolerance of indigenous plant or animal. To survive the
extreme temperatures, both marine and land-based plants and animals have
started to migrate towards the poles. Those species, and in some cases, entire
ecosystems, that cannot quickly migrate or adapt, face extinction. The IPCC
estimates that 20-30 percent of plant and animal species will be at risk of
extinction if temperatures climb more than 1.5° to 2.5°C.
4. IMPACTING PEOPLE
The changes to weather and ecosystems will also
affect people more directly. Hardest hit will be those living in low-lying coastal
areas, and residents of poorer countries who do not have the resources to adapt
to changes in temperature extremes and water resources. As tropical
temperature zones expand, the reach of some infectious diseases, such as
malaria, will change. More intense rains and hurricanes and rising sea levels
will lead to more severe flooding and potential loss of property and life.
One inevitable consequence of global warming is sea-level rise. In the face of higher sea levels and
more intense storms, coastal communities face greater risk of rapid beach erosion from destructive
storms.
Hotter summers and more frequent fires will
lead to more cases of heat stroke and deaths, and to higher levels of near-surface
ozone and smoke, which would cause more ‘code red’ air quality days. Intense
droughts can lead to an increase in malnutrition. On a longer time scale, fresh
water will become scarcer, especially during the summer, as mountain glaciers
disappear, particularly in Asia and parts of North America.

6. On the flip side, there could be “winners” in a
few places. For example, as long as the rise in global average temperature stays
below 3 degrees Celsius, some models predict that global food production could
increase because of the longer growing season at mid- to high-latitudes,
provided adequate water resources are available. The same small change in
temperature, however, would reduce food production at lower latitudes, where
many countries already face food shortages. On balance, most research suggests
that the negative impacts of a changing climate far outweigh the positive
impacts. Current civilization—agriculture and population distribution—has
developed based on the current climate. The more the climate changes, and the
more rapidly it changes, the greater the cost of adaptation.
Ultimately, global warming will impact life on
Earth in many ways, but the extent of the change is largely up to us. Scientists
have shown that human emissions of greenhouse gases are pushing global
temperatures up, and many aspects of climate are responding to the warming in
the way that scientists predicted they would. This offers hope. Since people are
causing global warming, people can mitigate global warming, if they act in
time. Greenhouse gases are long-lived, so the planet will continue to warm and
changes will continue to happen far into the future, but the degree to which
global warming changes life on Earth depends on our decisions now.
HOW TO PREVENT GLOBAL WARMING
To put a serious dent in the global warming problem,
there are endless preventive measures to consider that involves individual,
group, community, family, state, and country wide efforts. Some global
warming prevention tips are as simple as changing a few habits within the
household to more permanent measures, such as passing laws that directly
decreases the issue. Below you will find 101 ways to become an active part of
reversing the threatening trend of global warming:
1) Drive Less:
When you decrease the times you take the car out for a spin, you not only
reduce the consumption of gas, but also reduce the amount of carbon dioxide
that reaches the air.
2) Tree Planting:
Planting just one tree has the power to absorb one ton of carbon dioxide over its
life span.
3) Bike to the Store:

7. Not only will you receive a healthy dose of exercise, but you will also spare the
environment the pollution caused by using your car as a main source of
transportation.
4) Join a Carpool:
When you group up with co-workers living in the neighborhood and take one
car to work, you will contribute to creating fewer cars on the road, which equals
less pollution in the air.
5) Switch Light Bulbs:
When you replace a regular light bulb with a compact fluorescent, you will save
150 pounds of carbon dioxide each year. Once this type of light bulb burns out,
it is also important to follow the proper procedures regarding disposal.
6) Recycle Household Waste:
Some households are able to save up to 2,400 pounds of carbon dioxide per year
when they recycle just half of their waste.
7) Buy Recycled Products:
When you support recycled products, you not only save energy and resources,
but also reduce the amount of waste that accumulates in local landfills.
8) Start a Compost Pile:
While recycling centers take care of paper recycling and other items, such as
batteries, plastics, and metals, starting a compost pile helps reprocess organic
materials (egg shells, newspaper, and food scraps) into a nutrient-rich soil for
gardens and other landscaping needs.
9) Save Your Engine:
You should also consider turning off your car engine when you face an idle
vehicle for long periods of time, which helps to reduce air pollution.
10) Replace Car Air Filter:
To reduce the amount of air pollution produced by your car, you should replace
your air filter on a regular basis.