Earth Science 21.3 Climate Changes

1. Earth Science 21.3 Climate Changes Climate Changes

2. Earth Science 21.3 Climate Changes • Climate is always changing. Some of these changes are short term. • Other changes occur over long periods of time. • Still other climate changes are a result of natural processes, such as floods caused by El Nino. • With the growing industrialization of the world, other climate changes are occurring due to the impact of man on the environment.

3. Earth Science 21.3 Climate Changes • Many different natural processes can cause climates to change. • Many of these act over long periods of time while some occur at a relatively fast pace on the scale of geological time. • All together, these combinations of changes make for a very complex picture of what actually controls our planet’s climate and where our future climate is headed.

4. Earth Science 21.3 Climate Changes Plate Tectonics: • Geographic changes in Earth’s land and oceans due to plate tectonics causes changes in climate over very long time scales. • Due to plate tectonics, oceans open and close over time, changing ocean circulation patterns. • Large supercontinents, like Pangaea, develop monsoon climates as happened in Asia.

5. Earth Science 21.3 Climate Changes • Most importantly, mountain building cools global climates by removing carbon dioxide from the atmosphere. • For example, Earth has been cooling over the past 50 million years because of the collision of India and Asia which created the Himalayas.

6. Earth Science 21.3 Climate Changes • In this process, mountains weather and erode quickly, and sediments wash down rivers and into the ocean where they form carbonate rocks such as limestone. • The carbon in limestone begins as carbon dioxide from the atmosphere. Weathering removes carbon dioxide from the atmosphere and buries it on the sea floor. • Before India collided with Asia, there was three times as much carbon dioxide in the atmosphere as there is now.

7. Earth Science 21.3 Climate Changes Earth’s Orbital Motions: • Changes in the shape of the Earth’s orbit and the tilt of the Earth’s axis of rotation affect global climates over intermediate time scales. • Earth’s orbit is always elliptical. But over 100,00 to 400,000 year periods, the path around the sun becomes more or less elliptical. This change is called eccentricity of orbit. • This change in shape brings Earth closer to and than further from the sun.

8. Earth Science 21.3 Climate Changes Earth’s Orbital Motions: • This proximity to the sun affects global climates: Earth is warmer when it is closer to the sun. • The tilt of Earth’s orbit also changes with respect to the solar system, with a 100,000 year cycle. • The tilt and direction of Earth’s axis of rotation also changes over periods of about 20,000 to 40,000 year cycles. • The tilt of Earth’s axis changes by as much as 3 degrees. This affects the severity of the seasons by creating greater or lesser temperature differences between winter and summer.

9. Earth Science 21.3 Climate Changes Ocean Circulation: • 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 an 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 periods. • Also, some areas that receive abundant rainfall may experience dry periods when the ocean circulation pattern changes.

10. Earth Science 21.3 Climate Changes Solar Activity: • In general, the sun has been giving off increasing amounts of energy over it’s lifetime. • Over short time scales, fluctuations in the amount of solar radiation can change global climates. • An increase in sunspots appears to correspond with warm periods in Europe and North America. • Fewer sunspots seem to correlate with periods of cooler weather conditions. For example, the “Little Ice Age” in Europe during the 1600s occurred when there were very few sunspots. • This process is not understood and is under investigation by scientists. SUNSPOT CYCLES

11. Earth Science 21.3 Climate Changes Volcanic Eruptions: • Volcanic eruptions can affect climates as well by sending large amounts of ash and smoke aloft when an eruption occurs. • Volcanic eruptions can also send minute particles containing sulfur into the atmosphere. • If the amount of these fine particles discharged is substantial enough, short term changes can occur in Earth’s temperatures as sunlight is blocked out.

12. Earth Science 21.3 Climate Changes Volcanic Eruptions: • Volcanic ash, dust, and sulfur based aerosols in the air increase the amount of solar radiation that is reflected back into space. • This causes Earth’s lower atmosphere levels to become cooler. • Over long time scales however, volcanic eruptions can raise global temperatures by adding gases like carbon dioxide to the atmosphere, increasing the greenhouse effect.

13. Earth Science 21.3 Climate Changes Human Impact on Climate Change: • Natural processes have certainly contributed to many climatic changes throughout Earth’s 4.6 billion year history. • These processes will also cause some of the future shifts in Earth’s climate. • But human activities have contributed and will continue to contribute to global climate change.

14. Earth Science 21.3 Climate Changes The Greenhouse Effect: • The Greenhouse Effect is a natural warming of both Earth’s lower atmosphere and Earth’s surface. • The major gases involved in the Greenhouse Effect are water vapor, carbon dioxide, and methane. • These greenhouse gases, as they are often called, are transparent to solar radiation, and therefore much of this energy reaches Earth’s surface. • Most of this solar energy is than reradiated skyward.

15. Earth Science 21.3 Climate Changes The Greenhouse Effect: • The greenhouse gases are good absorbers of the heat radiated back from the Earth. • These gases maintain warm temperatures in the Earth’s lower atmosphere, making Earth habitable for many living things. • Without the Greenhouse Effect, the Earth would be far too cold to support life as we know it. • However, an increase in the Greenhouse Effect could raise temperatures considerably and alter conditions on Earth as well.

16. Earth Science 21.3 Climate Changes The Greenhouse Effect: • Studies indicate that human activities for the past 200 years or so have strengthened the Greenhouse Effect. • Carbon dioxide levels in the atmosphere have risen at an alarming level since the 1850s as the burning of fossil fuels has increased. • The clearing of forests also contributes to an increase in carbon dioxide because this gas is released when vegetation is burned or when it decays.

17. Earth Science 21.3 Climate Changes • As a result of the increases in carbon dioxide levels, as well as other greenhouse gases, global temperatures have increased. This increase is called Global warming. • Scientific evidence shows that , during the 20th century, Earth’s average temperatures increased by about 1 degree Celsius. • Scientists predict that by the year 2100, temperatures could increase by more than another 5 degrees Celsius.

18. Earth Science 21.3 Climate Changes • Scientists base their predictions about global warming on computer models of change in Earth’s atmosphere called climate models. • These models involve huge amounts of data n temperature, precipitation, and other variables. • But climate models can not describe Earth’s atmosphere completely. For this reason, the results of a climate model are always an approximation. • What follows is one prediction of how temperature increases could affect the Earth.

19. Earth Science 21.3 Climate Changes • Warmer surface temperatures increase evaporation rates. • This in turn increases the amount of water vapor in the atmosphere. • Water vapor is an even more powerful absorber of radiation emitted by Earth than is carbon dioxide. • Therefore, more water vapor in the atmosphere will magnify the effect of carbon dioxide and other gases.

20. Earth Science 21.3 Climate Changes • 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 Earth’s surface. • This, in turn, will magnify the temperature increase created by higher levels of greenhouse gases.

21. Earth Science 21.3 Climate Changes • The melting of sea ice and ice sheets will also cause a global rise in sea level. • This will lead to shoreline erosion and coastal flooding. • Warmer oceans could also lead to stronger and more frequent storms, including major hurricanes.

22. Earth Science 21.3 Climate Changes • Scientists also expect that weather patterns will change as a result of the projected global warming. • More intense heat waves and droughts in some areas and fewer such events in other places are predicted. • Hotter, more arid conditions have already led to more forest fires in the Western United States.

23. Earth Science 21.3 Climate Changes