Transcript Climate Change 17.3

Climate Change 17.3
Ck12 Earth Science Text
El Niño
A natural climate variation in which the trade
winds weaken or reverse directions, and warm
water accumulates on the ocean surface off of
South America.
global warming
Warming of Earth’s atmosphere because of the
addition of greenhouse gases. The increase in
average global temperature is caused by human
activities.
La Niña
A natural climate variation in which the trade
winds are stronger than normal and surface water
off of South America is cold.
Milankovitch cycles
Cycles adding up to variations of around 100,000
years regarding Earth’s position relative to the
Sun that affect global climate.
slash-and-burn agriculture
Plants are slashed down and then burned to clear
the land for agriculture.
sunspot
Cool, dark area on the Sun’s surface that have
lower temperatures than surrounding areas;
sunspots usually occur in pairs and come and go
on an 11-year cycle.
Pleistocene
Epoch
1.8 million
to 10,000
years ago
How different were the temperatures
during the ice age?
• The average global temperature during glacial
periods was only about 5.5 degrees Celsius
(or 10 degrees Farenheit) less than Earth’s
current average temperature.
• Temperatures during the interglacial periods
were about 1.1 degrees Celsius (or 2.0
Farenheit) higher than today
• The Medieval Warm Period from 900 to 1300 A.D.
allowed Vikings to colonize Greenland and Great Britain
to grow wine grapes.
The Little Ice Age, from the 14th to 19th centuries, the Vikings
were forced out of Greenland and humans had
to plant crops further south.
What about short-term changes in climate?
• The largest and most important of these is the
oscillation between El Niño and La Niña
conditions.
• In the news……January 2007
• Can you explain that?...El-Nino explained
El-Nino
• Water temperatures reach 82 degrees Farenheit.
• Trade winds weaken or reverse direction and blow towards
South America.
• Warm water travels eastward towards South America.
• Upwelling (cold water brought up from ocean depths)
stops.
• With less nutrients from the upwelling…the plankton
population goes down.
• Since plankton are the base of the ocean food chain, if
they decrease in number the fish that feed on them also
decrease.
• Animals that feed on the fish also decrease as well.
• Local economy is affected.
Other effects of El-Nino
• Some regions receive more than average
rainfall, including the west coast of North and
South America, the southern United States,
and Western Europe.
• Drought occurs in other parts of South
America, the western Pacific, southern and
northern Africa, and southern Europe.
Causes of Long-term Climate
Change………….changes in
in the amount of energy the Sun produces over
years.
in the positions of the continents over millions of
years.
in the tilt of Earth’s axis and orbit over thousands of
years.
that are sudden and dramatic because of random
catastrophic events, such as a large asteroid impact.
in greenhouse gases in the atmosphere, caused
naturally or by human activities.
Solar Variation
• The amount of energy the Sun radiates is
variable.
• When the number of sunspots is high, solar
radiation is also relatively high.
• The Little Ice Age corresponded to a time
when there were no sunspots on the Sun.
Plate Tectonics
• Plate tectonic movements can alter climate.
• Over millions of years as seas open and close, ocean
currents may distribute heat differently.
• For example, when all the continents are joined into
one supercontinent (such as Pangaea), nearly all
locations experience a continental climate.
• When the continents separate, heat is more evenly
distributed.
Milankovitch Cycles
The Earth goes through regular variations in its
position relative to the Sun in three ways….
1. Shape of Earth’s Orbit
• The shape of the Earth’s orbit changes slightly as it
goes around the Sun.
• The orbit varies from more circular to more
elliptical in a cycle lasting between 90,000 and
100,000 years.
• When the orbit is more elliptical, there is a greater
difference in solar radiation between winter and
summer.
2. The planet wobbles on its axis of rotation.
At one extreme of this 27,000 year cycle, the
Northern Hemisphere points toward the Sun when
the Earth is closest to the Sun.
• Summers are much warmer and winters are
much colder than now.
At the opposite extreme, the Northern Hemisphere
points toward the Sun when it is farthest from the
Sun.
• This results in chilly summers and warmer
winters.
3. The planet’s tilt on its axis varies
between 22.1 and 24.5 degrees.
• Seasons are caused by the tilt of Earth’s axis of
rotation, which is at a 23.5 degree angle now.
• When the tilt angle is smaller, summers and
winters differ less in temperature.
• This cycle lasts 41,000 years.
When these three variations are charted out, a
climate pattern of about 100,000 years emerges.
• Are we due to have another ice age?
• Ice ages correspond closely with Milankovitch
cycles.
• Since glaciers can form only over land, ice ages
only occur when LARGE landmasses (e.g.
Pangaea) cover the polar regions.
Changes in Atmospheric Greenhouse
Gas Levels
• What have you learned already?
• A decrease in greenhouse gas levels decreases
global temperature and an increase raises air
temperature.
Natural processes add and remove CO2 (carbon
dioxide) from the atmosphere.
• Processes that add CO2
– volcanic eruptions
– decay or burning of organic matter
• Processes that remove CO2
– absorption by plant and animal tissue.
Carbon dioxide is the most important greenhouse
gas that human activities affect because it is so
abundant.
• What are other greenhouse gases?
–water
–methane (livestock)
–CFCs
–ozone (vehicle exhaust)
How are humans affecting global
warming?
• Let’s take a look!
• NASA explains
What are effects of global warming?
Glaciers melt, increasing ocean levels and
decreasing some polar animals habitats.
Mating and migrations take place earlier in the
spring months
Some regions that were already marginal for
agriculture are no longer farmable because they
have become too warm or dry.
What are effects of global warming?
Oceans will become slightly more acidic, making it
more difficult for creatures with carbonate shells to
grow, and that includes coral reefs.
Plant and animal species seeking cooler temperatures
will need to move poleward.
Decreased snowpacks, shrinking glaciers, and the
earlier arrival of spring will all lessen the amount of
water available in some regions of the world,
including the western United States and much of Asia.
What are effects of global warming?
• Weather will become more extreme with heat
waves and droughts.
• Hurricanes are likely to become more severe and
possibly more frequent.
• Tropical and subtropical insects will expand their
ranges, resulting in the spread of tropical diseases
such as malaria, encephalitis, yellow fever, and
dengue fever.
Let’s check the review questions…..
• #1-14 pages 612 and 613
1. Why is the climate currently
warming?
2. Why does sea level rise and fall
during interglacial and glacial periods?
3. How can the human history of
Greenland be related to climate
cycles?
4. If climate has been much warmer in
Earth history, why do we need to
worry about global warming now?
5. When the weather along coastal
California is especially rainy with
many winter storms, what is likely to
be happening in the equatorial Pacific?
6. The Peruvian anchovy fishery
collapsed in 1972. Using what you
know about climate and food
webs, can you devise an
explanation for this event?
7. What two events must occur for
there to be an ice age?
8. What human activities increase
greenhouse gases in the
atmosphere? Explain.
9. Why are CO2 emissions projected
to increase during the next few
decades?
10. What role will the developed
nations play in increasing CO2
emissions in the next few decades?
11. Why do storms increase in
frequency and intensity as global
temperatures increase?
12. Earth is undergoing some important
changes, some of which are known
about because of and monitored by
satellites. Describe the sort of global
change that satellites can monitor.
13. What will happen if sea level rises
by 60 cm (2 feet) by the end of this
century?
Which locations will be hardest hit?
14. What can be done to reduce
greenhouse gas emissions?