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21.3- Climate Changes
Earth Science Standards: 4c, 6c, 6d
Vocabulary
greenhouse effect, global warming
Like most conditions on Earth, climate is always changing. Some of these changes are short-term.
Others occur over long periods of geologic time. Some climate changes are the result of natural processes, such
as volcanic eruptions shown in figure 14. others are related to human activities. In this section, you will learn
about some of the ways in which climate changes.
Natural Processes That Change Climate
Many different natural processes can cause a climate to changes. Some of the climate-changing processes that
you will learn about include volcanic eruptions as well as changes in ocean circulation, solar activities, and
Earth motions.
Volcanic Eruptions As you can see in figure 14, volcanic eruptions can emit large volumes of ash and dust
into Earths atmosphere. What you can’t see in the photograph is that volcanic eruptions also send minute
particles containing sulfur, into the air. If that volume of theses very fine particles called aerosols, is great
enough, it causes short-term changes in Earths surface temperature. Can you hypothesize why?
The presence of aerosols (volcanic ash, dust, and sulfur-bases aerosols) in the air increases the amount of
solar radiation that is reflected back into space. This causes Earth’s lower atmosphere to cool.
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Ocean circulations Recall from chapter 19 that El Nino is a change in ocean circulation that causes parts of
the eastern tropical Pacific Ocean to become warmer than usual. These changes in the ocean circulation also
can result in short-term climate fluctuations. For example, some areas that are normally arid receive large
amounts of rain during El Nino. Refer to figure 15. also, some regions that receive abundant precipitation may
experience periods when ocean circulation patterns change.
Solar Activity The most studied hypothesis of the causes of climate change are based on changes in the output
of solar energy. When the sun is most active, it contains dark blemishes called sunspots. The formation of the
sunspots appears to correspond with warm periods in Europe and North America. Although some variations in
solar output may cause short-term climate changes, no evidence exists for long-term variations due to solar
activity
Earth Motions A number of Earth motions are thought to cause changes in the climate. Most of these changes
are long-term changes. Tectonic plate movements, for example, cause the crust and upper mantle to move
slowly over the Earths surface. These movements cause ocean basins to open and close and change the position
of landmass. Uplift of new mountain ranges can also change climate. For example, the formation of the
Himalayas caused dry conditions on the vast Tibetan plateau that lies in the Himalayas; rainshadow. These
geographic changes in Earths land and water bodies cause changes in climate.
Changes in the shape of Earths orbit and the lilt of Earth on its axis are the other Earth motions
that effect global climate. Earths orbit, or path around the sun, is always elliptical. But over 100,000-year
period, the path becomes more and less elliptical. This change in shape brings Earth closer then farther from the
sun. this effects global climates. Like its Orbit, the tilt of the Earth on its axis changes about 2 degrees over
41,000-year period. Because the angle of the tilt, the severity of the seasons also change. The smaller the tilt the
smaller that temperature is between summer and winter.
√Checkpoint: identify the natural processes that can result in climate changes
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Human impact on climate change
Natural processes have certainly contributed to many climate changes throughout Earths 4.6-billion year
history. These processes will also cause some of the future shifts in Earths climate. But human activities have
contributed and will contribute to global climate change.
The Greenhouse Effect- the greenhouse effect is a natural warning of both Earths lower atmosphere
and Earths surface. The major gases involved in the greenhouse effect are water vapor and carbon dioxide.
These greenhouse gases are they are often called, are transparent to incoming solar radiation and therefore much
of this energy reaches Earths surface. Most of this energy is reradiated skyward. The greenhouse gases are food
absorbers of Earths radiation. These gases maintain warm temperature in the lower atmosphere, making earth
habitable for living things. Without the greenhouse effect, earth would be too cold to support life. But an
increase in the greenhouse effect could also prove devastating.
Studies indicate that human activities for the past 200 or so years have strengthened the greenhouse
effect. As you can see in figure 16, carbon dioxide levels in the air have risen at a rapid pace since about 1850
.Much of the greenhouse gas has been added by the burning of fossil fuels. The clearing of forest also
contributes to an increase in carbon dioxide because this gas is released when vegetation is burned or when it
decays.
Global Warming As a result of increases in carbon dioxide levels, as well as other greenhouse gases,
global temperatures have increased. This increase is called global warming. Figure 17 shows that during
the twentieth century, Earth’s average surface temperatures increased about 0.6 C. Scientist predict that by the
year 2100, temperatures will increase by 1.4 C to 5.8 C.
Scientist bases their predictions about global warming on computer models of change in Earth’s
atmosphere called climate models. Climate models are complex computer programs. These models involve
huge amounts of data on temperature, precipitation, and other variables. But climate models cannot describe
Earth’s atmosphere completely. For this reason, the results from a model are always an approximation. What
follows is one prediction of how temperature increase could affect Earth.
Warmer Surface temperatures increase e evaporation rates. This, in turn, increases the amount of water
vapor in atmosphere. Water vapor is an even absorber of radiation emitted by Earth than is carbon dioxide and
other gases.
Temperature increases will also cause sea ice to melt. Ice reflects more incoming solar radiation than
liquid water does. The melting of the ice will cause a substantial increase in the solar energy absorbed at the
surface. This, in turn, will magnify the temperature increase created by higher levels of greenhouse gases. The
melting of sea ice and ice sheets will also cause a global rise in sea level. This will lead to shoreline erosion and
cause costal flooding.
Scientist also expect the weather patterns will change as a result of the global warming. More intense
heat waves and droughts in some regions and fewer such events in other places are also predicted.
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21.3 Section Assessment
1. Describe four natural processes that can cause climate
change.
2. What is the greenhouse effect?
3. What is global warming?
4. What are some of the possible effects of global
warming?
Critical Thinking
5. Formulating Hypotheses Which would have a longer
effect on climate changes- volcanic ash and dust or the
same volume of sulfur-based aerosols? Why?
6. Formulating Conclusions How do you think cloud
cover might change as the result of global warming?
7. Synthesizing How might global warming affect Earth’s
inhabitants, including humans?
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