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Sec. 14 - 3 Earth’s climate is constantly changing on many different timescales. Review Vocabulary glacier: large, moving mass of ice that forms near Earth’s poles and in mountainous regions at high elevations I. Long-Term Climatic Changes A. Ice ages 1. Glaciers advance and retreat 2. Average global temperatures decreased by 5°C 3. Snowfall increased B. Interglacial Intervals 1. Warm periods between ice ages 2. The most recent ice age ended about 10,000 years ago II. Short-Term Climatic Changes A. Seasons - caused by regular variations in daylight, temperature, and weather patterns 1. Changes in solar radiation a. Tilt of Earth’s axis b. Earth is a sphere 2. Opposite in N & S hemispheres B. El Niño - warm ocean current that occasionally develops off the western coast of South America Under normal conditions, trade winds and ocean currents move warm water west across the Pacific Ocean. During El Niño, warm water surges back toward South America, changing weather patterns. 1. Warm water heats surrounding air and convection current strengthen a. NW South America becomes warmer and wetter 2. Upper level winds move system east a. Violent storms in CA and Gulf Coast b. Storms where it’s usually dry c. Drought where it’s usually wet 3. Strong Trade Winds a. La Niña b. South American coast becomes colder III. Natural Causes of Climatic Changes A. Solar activity The Maunder minimum is the term used to describe the period of low numbers of sunspots, from 1645 to 1716. This period closely corresponds to an unusually cold climatic episode called the Little Ice Age. Studies indicate that increased solar activity coincides with warmerthan-normal sea surface temperatures, while periods of low solar activity, such as the Maunder minimum, coincide with colder sea surface temperatures. Figure 14.18 Page 390 B. Earth’s orbit The shape of Earth’s elliptical orbit appears to change, becoming more elliptical, then more circular, over the course of a 100,000-year cycle. Fig. 14.19 Page 390 Scientists hypothesize that a more elliptical orbit around the Sun could produce significant changes in Earth’s climate. C. Earth’s tilt At present, the angle of the tilt of Earth’s axis is 23.5°. However, the angle of tilt varies from a minimum of 22.1° to a maximum of 24.5° every 41,000 years. Fig. 14.20 Page 391 If the angle of the tilt of Earth’s axis decreased, there would be less temperature contrast between summer and winter. D. Earth’s wobble Over a period of about 26,000 years, Earth wobbles as it spins around on its axis. Currently, the axis points toward the North Star, Polaris. Fig. 14.21 Page 391 Earth’s wobble determines the timing of the seasons. When the axis points toward the star Vega in 13,000 years, the northern hemisphere will experience summer during the time now associated with winter. E. Volcanic activity 1. Aerosols a. dust-sized particles that are released during major volcanic eruptions b. Remain suspended for several years c. blocking incoming solar radiation d. lowers global temperatures Sec. 14 - 4 Impact of Human Activities Over time, human activities can alter atmospheric conditions enough to influence changes in weather and climate. Review Vocabulary radiation: transfer of thermal energy by electromagnetic waves I. Influence on the Atmosphere A. The greenhouse effect 1. Natural heating of Earth’s surface caused by certain atmospheric gases 2. Can lead to a rise in global temperatures, known as global warming Please click the image above to view the video. II. Global Warming Temperatures worldwide have shown an upward trend over the past 200 years, with several of the warmest years on record having occurred within the last two decades. Fig. 14.24 Page 394 A. Burning fossil fuels 1. Main source of atmospheric carbon dioxide 2. Coal, oil, and natural gas 3. Also releases other greenhouse gases a. methane b. nitrous oxide B. Deforestation 1. The mass removal of trees 2. Increases levels of atmospheric carbon dioxide a. Photosynthesis is reduced b. carbon dioxide remains in the atmosphere C. Environmental efforts Earth’s climate is constantly changing on many different timescales. Climate change can occur on a longterm or short-term scale. Changes in solar activity have been correlated with periods of climate change. Changes in Earth’s orbit, tilt, and wobble are all associated with changes in climate. Over time, human activities can alter atmospheric conditions enough to influence changes in weather and climate. The greenhouse effect influences Earth’s climate. Worldwide temperatures have shown an upward trend over the past 200 years. Human activities can influence changes in weather and climate. Individuals can reduce their environmental impact on climate change.