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Explore the impacts of El Niño and La Niña on global climate, the Earth's history of temperature variations, and factors influencing long-term climate changes. Discover how solar variation, plate tectonics, and Milankovitch cycles play a role in shaping our climate over millions of years.
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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 hadto 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 pointstoward the Sun when the Earth isclosest to the Sun. • Summers are much warmer and wintersare much colderthannow. At the oppositeextreme, the NorthernHemispherepointstoward the Sun whenitisfarthest from the Sun. • Thisresults in chillysummers and warmerwinters.
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
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 behappening 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?
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?
