2. Natural Climate Changes Processes Resulting in Changes in Climate Trends Over Time

3. I. Short Term Natural Climate Changes A. Changes in climate trends, measured in months to years 1. Seasons The tilt of the earth’s axis causes different areas of Earth to receive different amounts of solar radiation This results in variations in daylight, temperature and weather patterns When the north pole is pointed toward the sun, the northern hemisphere experiences summer and the southern hemisphere experiences winter (A) During spring and fall, neither pole points toward the sun (B)

4. 2.Volcanic Activity Volcanic dust can remain suspended in the atmosphere for several years This blocks incoming solar radiation and lowers global temperatures 1991 eruption of Mt. Pinatubo1980 eruption of Mt. Saint Helens

5. 3.El Niño Caused by a warm ocean current that occasionally develops off the west coast of South America- due to shift in wind patterns Negative Effects of El Nino: Wet, stormy weather occurs in areas that are normally dry Drought conditions occur in areas that are normally wet Violent storms brought to California and the Gulf Coast Extensive property damage and untold human suffering Positive Effects of El Nino: Fewer and less severe hurricanes in the Atlantic ocean regions

6. Video- El Niño Consequences CNN 2003

7. Normal: cool dry climate Pacific Ocean Cold water is transported north from Antarctica. Due to winds, Waters are warm in W. Pacific Normal ConditionsEl Niño Conditions Pacific Ocean The cool dry climate becomes warm and wet! Westerly trade winds weaken and warm water flows east Antarctica

8. II. Long Term Natural Climate Changes A. Changes in climate trends, measured over tens to hundreds of thousands of years 1. Ice Ages Glaciers have alternatively advanced and retreated over the past 2 million years Ice Ages are periods of extensive glacial coverage Global temperatures drop 5 degrees Celsius on average Most recent Ice Age ended 10,000 years ago

9. 2.Earth’s Orbit Every 100,000 years, the shape of Earth’s orbit changes, becoming more elliptical, then more circular When the orbit elongates, earth passes closer to the sun and temperatures become warmer than normal When the orbit is more circular, temperatures dip below average

10. 3.Earth’s Axis The angle of tilt varies from 22.1º to 24.5º every 41,000 years Changes in angle cause seasons to become more severe A decreased tilt might cause winters to be warmer than normal and summers to be cooler than normal Changes in tilt may be responsible for Ice Ages

11. 4.Earth’s Wobble Over a period of 26,000 years, Earth wobbles as it spins on its axis Currently the axis points toward the North Star (Polaris) and winter occurs in the northern hemisphere when Earth is closest to the sun When the axis tilts toward Vega, winter will occur in the northern hemisphere when Earth is farthest from the sun This will cause warmer summers and colder winters than those we now experience