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Climate Change, Greenhouse Effect and Global Warming
Earth’s Climate: A Dynamic System
The Earth is a unique planet where our atmosphere, the oceans and soils combine to support a web
of life of diversity and continual change. The daily needs of more than six billion people now stress
the limits of this naturally regulated system.
Is Our Climate Changing?
Weather changes both rapidly and slowly. The passage of a thunderstorm can change a bright sunny
day into a dark, windy, rainy one in less than an hour. Farmers know that in one year the amount
and timing of rainfall can be nearly ideal for growing crops, while the next year might bring drought
or floods. In some years no hurricanes reach the Atlantic Coast, while in other years coastal states
are battered by one storm after another. All of these things are dictated by the Earth’s climate.
Is the Earth’s climate changing? One extreme summer in the United States can’t answer that
question. Our picture of the climate develops slowly as we watch many seasons pass. Only by
comparing measurements taken over many years and decades can we sense the shifting patterns of
climate. The hottest ten years in recent history have taken place since 1987. Climate is a complex
system that ties together the atmosphere, oceans, land surface and the living kingdoms of plants and
animals. Climate describes the weather over a long period of time.
The Earth has experienced major climate changes long before humans inhabited the planet. The
dinosaurs roamed a world much warmer than today. The Earth has also gone through an ice age that
sent massive glaciers spreading over North America and Europe. Animals and plants have been
forced to either go extinct or to adapt to new conditions. Such natural shifts in climate have
distinguished the different eras in Earth’s history. Climate change is a natural phenomenon due to
solar variability, volcanic activity, biological evolution and El Nino. These changes can influence
global warming and global cooling.
We now face the prospect of a different kind of climate change. Many scientists believe this change
is being brought on primarily by human actions. Our industry, agriculture and daily living cause
important gases such as carbon dioxide (CO2) and methane (CH4) to accumulate in the atmosphere.
Scientists predict severe consequences may await us in the not too distant future if we do not change
our behaviors.
The Light from Above
If we were to look at our Earth from space, we would see a multi-colored sphere. Clouds and snowcoated lands create patches of cottony white that interweave with the royal blue background of the
oceans. Breaks in the cloud cover would reveal the continents as brown hues while lighter splotches
of color indicate desert regions.
The white areas make Earth a bright planet. About 30% of the sun’s radiation gets reflected
immediately back into space by the Earth’s atmosphere and snow. This is called the Albiedo Effect.
Solar energy that doesn’t reflect off clouds and snow is absorbed by the atmosphere and surface of
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the Earth. As the surface warms, it sends infrared radiation, or heat, back toward space. This type of
radiation resembles the warmth we feel when sitting at a distance from a hot stove or campfire.
Aside from gases in the atmosphere, clouds also
play a major climatic role. By reflecting solar
radiation away from Earth, some clouds cool the
planet. Satellite measurements have recently
proved that clouds exert a powerful cooling effect
on the Earth. In some areas, such as the tropics,
heavy clouds may markedly warm the regional
climate by reflecting the infrared heat back
towards the Earth. This trapping of heat near the
surface contributes to the Earth’s natural
greenhouse effect.
Clouds and greenhouse gases fit into something
called the global radiation budget. Just like a
well-constructed economic budget, the radiation
budget must balance itself. Solar energy reaching
Earth must equal the energy leaving the planet
otherwise the oceans would eventually boil away
or freeze solid.
Scientists warn that we are currently upsetting the
Earth’s radiation balance through activities such as
burning fossil fuels and cutting forests. These
actions cause carbon dioxide and other gases to
accumulate in the air and therefore strengthen
Earth’s greenhouse effect. We expect the planet’s
surface will warm up until a new radiation balance
emerges.
The Greenhouse Effect
Looking at other planets, we can see both stronger
and weaker greenhouse effects than that of Earth.
Our nearest neighbor, Venus, has a thick cloak of
carbon dioxide that heats the planet’s surface to an
average of 4200 C. Mars, with a mean surface
temperature hovering around –500C, has a very
thin atmosphere that provides little greenhouse
warming.
Earth’s atmosphere lets in rays of sunshine and
they warm the surface. The planet keeps cool by
emitting heat back into space in the form of
infrared radiation. But while the atmosphere is
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How do scientists study past climates?
If scientists had to rely on written
weather records for historical climate
information, they would be in trouble.
Such records only exist for the last 150
years or so. However, clues in the
environment can provide information
from thousands of years ago.
Ice cores -- Ice in polar-regions contains
air bubbles trapped thousands of years in
the past. Scientists can check the gases in
the bubbles and provide a good estimate
of the temperature at that time. Also, the
thickness of the ice layers gives
information about past climates.
Tree rings -- Trees can live for centuries,
and for each year of their lives they add a
ring of growth to their diameter. The
width of these rings can give scientists
information about climate during that
year of growth.
Fossils -- The bones of long-dead
animals indicate which species lived in
certain areas and when they were there.
Since each species has a set of food and
temperature requirements, scientists can
deduce the climate of their time and area.
Sediment cores -- Columns of sediment
from lake bottoms contain pollen grains
in each layer. The farther down the layer,
the older the sediment. After determining
the age of the layers, scientists can study
what plants were growing when the
sediment was deposited.
Archaeological records -- Humans have
left their traces throughout the world for
ages. How they lived and what they
needed to survive provide important
clues about the climates they
experienced.
fairly transparent to sunshine, it is almost opaque to infrared radiation. It traps the heat inside much
like a garden greenhouse. About 70% of the solar energy that reaches Earth passes through the
atmosphere and is absorbed at the surface. About 90% of the infrared radiation emitted by the
surface is re-absorbed by the atmosphere before it can slowly escape to space. The layer of air
surrounding the Earth contains important gases such as water vapor and carbon dioxide. These
gases absorb the heat radiated by the Earth’s surface and reemit their own heat at much lower
temperatures. The atmosphere “traps” the Earth’s radiation. This planetary warming mechanism is
called the “greenhouse effect.” The greenhouse effect is good, without it we would not be able to
live here. The atmosphere saves us
from a frigid fate.
If all greenhouse gases were
removed from the atmosphere, the
average surface temperature of
Earth would drop from its current
value of 60°F (15°C) to about 0°F
(-18°C). Earth would be a frozen
and nearly lifeless planet without
the greenhouse effect. It is the
distinctive molecular structures of
the greenhouse gases that make
them strong absorbers and emitters
of infrared radiation. About 99% of
air molecules are nitrogen (N2) and
oxygen (O2). They have simple structures consisting of two identical atoms. They have a relatively
minor effect on the transmission of solar and infrared radiation through the atmosphere because of
this simple structure.
Molecules with three or more atoms like water vapor (H2O), carbon dioxide (CO2), ozone (O3) and a
host of other trace gases can efficiently absorb and emit (give off) infrared energy. Though some of
these gases make-up only a tiny fraction of the atmosphere they can make significant contributions
to the greenhouse effect. The molecule that makes the largest contribution is water vapor. Water
vapor is the most important greenhouse gas. Because we have no direct control over it we focus on
the other greenhouse gases that we have more control over. An average water molecule stays in the
atmosphere only a few days from the time it evaporates from the surface to the time it falls out of
the atmosphere as precipitation. Because of this the water vapor content of the atmosphere adjusts
quickly to changes in surface temperature.
Why Are Greenhouse Gas Amounts Increasing?
Carbon dioxide gas makes-up a tiny fraction of the atmosphere. Only about one air molecule in
three thousand is CO2. Yet, despite their small numbers, CO2 molecules can have a big affect on the
climate. Carbon dioxide (CO2) has a much longer lifetime in the atmosphere than water vapor. It
can take 100 to 200 years to establish a new atmospheric balance if CO2 is suddenly added to the
atmosphere. That’s because the carbon in CO2 is cycled between the atmosphere and the ocean or
land surface by slow chemical and biological processes. Plants, for example, use CO2 to produce
energy in a process known as photosynthesis. Through millions of years of Earth’s history, trillions
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of tons of carbon were taken out of the atmosphere by plants and buried in sediments that eventually
became coal, oil or natural gas deposits. In the last two centuries humans have used these deposits at
an increasing rate as an economical energy source. In a similar way, cement manufacture releases
carbon atoms buried in carbonate rocks. Today human activities release about 5.5 billion tons of
carbon to the atmosphere every year through burning fossil fuels and cement manufacturing.
Approximately another 1.5 billion tons per year are released through land use changes such as
deforestation. These releases result in an increase of atmospheric CO2 of about one-half percent per
year. The burning of coal, oil and natural gas and the destruction of forests has raised the total
amount of atmospheric carbon dioxide by nearly 30% since the beginning of the industrial
revolution in the early 1800’s.
Other naturally occurring greenhouse gases
such as methane and nitrous oxide have been
increasing. Entirely man-made greenhouse
gases such as CFC’s have also been introduced
into the atmosphere. Many of these gases are
increasing more rapidly than carbon dioxide.
The amount of methane, or natural gas, in the
atmosphere has doubled since the Industrial
Revolution.
Greenhouse Gases and Global Warming
Since the Industrial Revolution, however,
atmospheric concentrations of the most
important human-influenced greenhouse gases
– CO2, methane and nitrous oxide – have
increased at an unnatural rate. In the last 200
years, CO2 levels have risen almost 30%,
methane levels have gone up 145%, and nitrous oxide levels have increased by 15%. Each
greenhouse gas differs in its ability to absorb heat in the atmosphere. Where are all these "extra"
greenhouse gases coming from? They are coming from our daily activities. Large-scale burning of
fossil fuels for industry and motor vehicles, intense agricultural activity, population growth, land
practices, mining and other human activities pump more and more greenhouse gases into the
atmosphere, creating a heightened greenhouse effect that leads to a higher average global
temperature. This is called global warming. While water vapor is the most important Greenhouse
Gas, humans have very little control over it.
Carbon dioxide (CO2) is the greenhouse gas that humans are contributing to most directly. Carbon
dioxide is a colorless, odorless gas which was naturally in the air before humans were around. Now
we continue to emit the gas into the air with our cars, our manufacturing, burning of rain forests and
our cutting down of trees. The destruction of trees creates a shortage of plants to remove CO2 from
the air. We also release CO2 into the atmosphere when we burn fossil fuels for the generation of
electricity.
Methane (CH4), also called marsh gas, is another greenhouse gas that was in the air, naturally,
before humans. It is used in industries as starting material for many other chemicals. This gas is
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lighter than air, colorless, odorless, nontoxic, and highly flammable. It is created naturally from
decomposing matter in swamps. Methane comes from cow burps, coal mining, natural gas fumes,
landfills and wood burning. Methane is also the gas your stomach may release after a hearty meal.
In other words, when animals burp, they release methane and add to global warming. Methane traps
over 21 times more heat per molecule than carbon dioxide.
CFCs or chlorofluorocarbons (also called Halocarbons) were never naturally in the air. They were
first manufactured in the 1940s. Because they do not readily react with other chemicals they can
have a lifetime in the atmosphere of more than 100 years. This gas was used mostly in aerosol
sprays cans such as spray paint and hair spray, refrigeration units, air conditioning, cleaning
solvents and packing materials. Using CFCs in aerosol sprays has now been banned in the United
States and most other parts of the world. Not only is it a greenhouse gas and keeps infrared light
from leaving, but it also damages the ozone layer. The ozone layer is a layer in the upper
atmosphere that keeps the sun's harmful ultraviolet rays from reaching us. Global warming and
ozone destruction have little to do with each other. CFCs trap more heat than any of the other
greenhouse gases.
Nitrous oxide (N2O) is given-off during agricultural and industrial activities and during combustion
of solid waste and fossil fuels. Nitrous oxide (N20) is more known under the nickname laughing gas.
Nitrous oxide, also called nitrogen monoxide, is a colorless, odorless, nonflammable gas which may
also attack the ozone layer. It is used in industry as an aerosol propellant. Nitrous oxide absorbs 310
times more heat per molecule than carbon dioxide.
Sources and Sinks
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The elements that compose greenhouse gases, (carbon, oxygen, nitrogen, etc.), normally cycle
through the environment between sources and sinks freely. Sources release elements to the
atmosphere. Sinks store the elements. Soil, oceans and trees tend to act as natural sinks for carbon.
Each year hundreds of billions of tons of carbon, in the form of CO2, are absorbed by soils, oceans
and trees. When trees are cut down and burned, the stored carbon is released into the atmosphere as
carbon dioxide. The burning of trees is a carbon source.
For two centuries, we've been releasing greenhouse gases into the atmosphere at unprecedented
rates while destroying forests and other natural sinks that could absorb those gases. We've created a
greenhouse that’s a little too effective while trying to improve the quality of life.
The Consequences of Too Many Greenhouse Gases
If the climate cycle were to follow its natural course, in a few thousand years the Earth would start
sliding into another ice age. But our activities threaten to send the climate speeding in another
direction toward global
warming. The build-up of
greenhouse gases and other
gases have already
enhanced the Earth’s
greenhouse effect. It may
take several decades to feel
the warming because
atmospheric temperatures
will rise significantly only
after the oceans of the world
have slowly warmed.
The increase in temperature
postponement may seem
like an advantage. It gives
us more time to prepare.
However, the time lag could
lead us to underemphasize
the importance of the
problem while we still have a chance to prevent drastic climate change. We have already committed
ourselves to some degree of warming even if we could instantly halt the buildup of greenhouse
gases in the atmosphere.
As human population and economic activities continue to grow, carbon dioxide emissions could
double again in the next three decades unless the nations of the world limit their consumption of
fossil fuels. Such action would benefit society in many ways. Through energy conservation we can
save substantial amounts of money and help reduce our nation’s dependence on foreign fuels.
Despite our uncertainty about future climate change we are already beginning to take certain steps
that will slow the buildup of greenhouse gases.
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Global Warming and Wisconsin
Global warming: It’s a phrase that has been heard on weather broadcasts and news reports, in
science classrooms and around supper tables since the early 1990s. It is a concept that seems far
removed from our everyday lives, something that concerns scientists digging into polar ice caps
thousands of miles away – not us in Wisconsin. But global warming and the changes it could cause
in world climate should concern us.
Historical records indicate the average global temperature increased in Wisconsin by 0.50 to 10 F
between 1890 and 1990. Thus, the Earth has warmed. This is where the term global warming
comes from. In the next 100 years, scientists predict the temperature may rise another 20 to 60 F.
Such increases have occurred previously in Earth’s history, but never over such a short time span. In
fact, the average global temperature has risen more in the last century than at any time in the past
10,000 years.
The great majority of scientific research agrees that between now and the end of this century the
globe will continue to warm up. It is difficult to predict what an increase in global temperature will
bring because of the various climatic factors. However, the results could significantly alter life in
Wisconsin. All of the items listed below are potential changes Wisconsin could face:
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wetter winters and drier summers with longer, hotter and more frequent heat waves
weather and climate changes that could require farmers to raise different crops
dairy cattle and other livestock stressed by heat exhaustion and growing pest populations
poor air quality and higher concentrations of ground-level ozone could causes health problems
warmer and more shallow river waters could hurt populations of cold-water fish like trout
denser algae blooms and lower oxygen levels in ponds and lakes
more frequent floods, droughts, forest fires and damaging storms
changes in tree species that could affect the forestry industry and wildlife populations
increases in disease-carrying insect populations
The Effects of Global Warming on Wisconsin
Because the models scientists use to study climate change are not precise enough to offer specific
predictions for an area as small as the state of Wisconsin, the following discussion is taken from
predictions for the upper Midwest region. While it’s fairly safe to say that global climate change
won’t turn our state into a tropical
paradise, scientists agree that it
could significantly alter the way we
live.
Weather and Climate
The upper Midwest may become
warmer and wetter, with the
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average temperature increasing by about 40 F. The increase doesn’t mean we’d simply up the daily
temperature by 4 degrees. A more likely scenario is that summer heat waves would be longer and
hotter and nighttime winter temperatures would not sink so low. Precipitation could increase by as
much as 10% on average, but much of the increased precipitation would come in the form of intense
storms, leading to flooding and more runoff. Precipitation patterns could also change, with more
rain coming in the winter and less in the summer. Less rain in the summer, paired with increased
evaporation caused by warmer temperatures, could trigger severe summer droughts.
Water Resources
Lake Superior water levels could drop over time by 1 to 1.5 feet, while Lake Michigan levels could
fall 3 to 8 feet. Such drops could result from longer and drier summers during which more of the
lakes’ waters would be claimed by evaporation.
Winters might have less snow and shorter periods of snow cover. Lowered Great Lakes levels could
strike a heavy blow to industries like shipping and hydropower generation. Smaller inland lakes
could also get shallower. Some ponds and wetlands might disappear, jeopardizing wildlife habitat,
tourism and recreation industries. Groundwater levels could drop significantly threatening drinking
water quality and quantity due to increased concentrations of pollutants.
Warmer water would encourage algae blooms and other aquatic plant overgrowth in the summer.
This would transform clear blue waters into a thick, smelly pea soup that turns off boaters, anglers
and swimmers. Algae blooms also make survival difficult for fish and other aquatic species. Coldwater species like trout could decline in number or disappear from their traditional areas altogether.
Decreased winter ice cover could disturb both lake ecology and the ice fishing season.
Agriculture
Anything that affects farming affects the state’s economy. Southern Wisconsin farms may begin to
resemble those in present-day Kansas. Wheat would do well, but the ideal range for corn and
soybeans would shift northward, and these crops might not grow as well in the soils of northern
Wisconsin. High levels of carbon dioxide in the atmosphere may actually increase crop production,
because certain plants can become larger and more productive in a CO2–rich environment.
However, gains in crop productivity might be counter-balanced by more frequent and severe
droughts, and by more weed, pest and disease problems.
Dairy and other livestock farmers might see productivity decline as their herds suffer from heat
stress, the feed supply is disrupted (from changing crop yields), and the water supply reduced.
Warmer, longer summers might encourage the growth of pest populations that could further stress
livestock and spread disease.
Forests and Wildlife
As temperature and precipitation patterns change, habitat ranges for plants and animals are expected
to shift northward. Some species might be able to migrate with their ideal habitat, but others,
especially those already endangered, could face extinction. Researchers predict that mixed northern
hardwood and oak forests would be transformed to oak savannas and grasslands within 30 to 60
years. Typical northern forests could completely disappear from Wisconsin along with the eastern
hemlock and the sugar maple.
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Human Health
More frequent and severe heat waves would threaten the elderly, especially those living alone, and
people suffering from cardiovascular and respiratory diseases. The U.S. Environmental Protection
Agency (EPA) projects that a 30 F warming could almost double heat-related deaths in Milwaukee
during a typical summer, from 30 to about 55.
A longer, hotter summer, along with increased emissions from power plants trying to keep up with
greater air conditioning demands, would likely intensify air pollution problems. This could result in
more and more serious cases of asthma, emphysema and lung disease for Wisconsin residents.
Wisconsin’s allergy season could lengthen because some plants would flourish in the extended
summer. Warmer weather might also be beneficial to disease-carrying insects like mosquitoes and
ticks, leading to more cases of Lyme disease, tick-borne encephalitis and possibly even malaria.
Finally, more frequent severe weather events like forest fires, floods and dangerous storms could
cause injuries and take lives and damage properties. All of these would increase insurance rates.
Responding to a Global Threat
The Wisconsin Department of Natural Resources (DNR) has completed several studies showing that
the use of energy-efficient technologies could reduce the state’s emissions of greenhouse gases with
little or no net cost. One study showed that if Wisconsin adopted improved energy efficiency
measures, we could realize a 12.5 million ton decrease in the growth of greenhouse gas emissions
by 2010 (compared to projected levels) and save $490 million in energy expenditures at the same
time. Another study predicted that investing in energy efficiency measures could create a $490
million increase in disposable income, a $41 million increase in gross state product and 8,500 new
jobs in 2010.
In 1992, 154 nations and the European Union adopted the United Nations Framework Convention
on Climate Change. It was a voluntary agreement to stabilize greenhouse gas emissions at 1990
levels. In December 1997 at a United Nations meeting in Kyoto, Japan, some industrialized
countries went a step further and agreed to the Kyoto Protocol, which required developed nations to
reduce their greenhouse gas emissions to an average of 5% below 1990 levels by 2008-2012.
Specific reduction commitments varied among nations. If the protocol had gone into effect for the
U.S., it would have required the U.S. to reduce greenhouse gas emissions to 7 percent below 1990
levels. The U.S. refused to sign the Kyoto Protocol. At current rates of activity, our nation stands to
increase its emissions to 30% above 1990 levels by 2010. Our country is already the world’s largest
emitter of greenhouse gases, contributing approximately 23% of global emissions despite having
only 5% of the world’s population.
How Can We Help?
Many of the things we can do to reduce greenhouse gas emissions offer personal benefits as well.
The biggest contribution individuals can make is to use less energy. By tuning cars, insulating
homes and using energy-efficient appliances, we can decrease our use of fossil fuels and save
money. We can car pool, use public transportation, walk or bike to our destinations. These activities
cut fuel consumption, decrease traffic congestion, decrease emissions of other air pollutants and
may even help us become healthier. Finally, we can purchase items with reusable, recyclable, or
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reduced packaging. All of these options help decrease the amount of energy and resources being
used to make new packaging.
Those willing to invest even more in guarding against climate change have further options.
Alternative energy sources like solar power, wind power and geothermal heat pumps can supply
home energy needs. Vehicles using propane, natural gas or ethanol, fuels that burn cleaner than
gasoline, are already on the roads. Hybrid cars, which use electricity from batteries along with
gasoline for power, are another viable alternative for transportation. Solar-powered cars and fuelcell cars, powered by hydrogen, may be available within the next 10 years.
Global Warming and Sea Level Rise
One of the most significant potential impacts of climate change is sea level rise that may cause
flooding of coastal areas and islands, shoreline erosion, and destruction of important ecosystems
such as wetlands. River water salinity may also be an issue. As global temperatures increase, sea
level rise already underway is expected to accelerate due to a thermal expansion of upper layers of
the ocean and melting of glaciers.
Over the last 100 years, the global sea level has risen by about 10 to 25 cm. On this time scale, the
warming and the consequent thermal expansion of the oceans may account for about 2-7 cm of the
observed sea level rise, while the observed retreat of glaciers and ice caps may account for another
2-5 cm. Other factors are more difficult to measure. The rate of observed sea level rise suggests that
there has been a net positive contribution from the huge ice sheets of Greenland and Antarctica, but
observations of the ice sheets do not yet allow meaningful measurement estimates of their
contributions. The ice sheets remain a major source of uncertainty in accounting for past changes in
sea level because of insufficient data about these ice sheets over the last 100 years.
Warmer temperatures also increase precipitation. Snowfall over Greenland and Antarctica is
expected to increase by about 5 percent for every 1°F warming in temperatures. Increased snowfall
tends to cause sea level to drop if the snow does not melt during the following summer, because the
only other place for the water to be is the ocean. (The amount of water in the atmosphere is less than
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Dairy and other livestock farmers may see productivity decline as a result of __43__ in their
animals.
If the U.S. had adopted the Kyoto Protocol, we would have been required to reduce greenhouse gas
emissions to __44__% below 1990 levels by 2008-2012. However, at the current rates our nation
stands to increase its emissions to 30 percent above 1990 levels by 2010.
The U.S. is the world’s largest emitter of greenhouse gases, contributing approximately __45__% of
global emissions despite having only __46__% of the world’s population.
The biggest contribution individuals can make is to __47__.
Considering all of these factors, the Intergovernmental Panel on Climate Change (IPCC) estimates
that sea level will rise __48__ cm by the year 2100.
List the nine potential changes Wisconsin could face if global warming continues: (write out)
49.
50.
51.
52.
53.
54.
55.
56.
57.
List five of the clues scientists use to study past climates:
58.
59.
60.
61.
62.
Short Answer Questions: Write the answers to these questions in your notebook.
63. What is the difference between climate and weather?
64. What is the greenhouse effect and why is it important to life on Earth?
65. What is the difference between global warming and climate change?
66. How does nature contribute to climate changes?
67. How have humans contributed to the global warming?
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