How Do Oceans Affect Weather and Climate?

How Do Oceans Affect Weather and Climate? In Learning Set 2, you explored how water heats up more slowly than land and also cools off more slowly than land. Weather is caused by events in the atmosphere. However, the atmosphere is part of a bigger system, the Earth system. Thermal energy and water constantly fl ow between the oceans and the atmosphere. In this section, you will explore the ways Earth s vast oceans affect weather and climate on the planet. By the end of this section, you should be able to identify how ocean temperatures affected weather in the summer and winter data you examined at the start of this Learning Set. As winds move air in the atmosphere, ocean currents move water in the oceans. This map shows the Pacific Ocean, the largest of Earth s oceans. ocean currents: movements of water in Earth s oceans caused by global circulation patterns. The question for this section asks how oceans affect weather and climate. Before you can answer the question, however, you must understand what causes ocean currents. Ocean currents are predictable pathways of water in the oceans. Global winds move air in the atmosphere, and ocean currents move water in oceans. You discovered how global winds are produced by convection and Earth s rotation. Similar forces affect the movement of ocean waters. WW 207

Learning Set 4 What Other Factors Interact to Cause Weather Changes? Just like air, water is a fl uid. In the previous section, you observed how convection currents cause water to move from warmer areas to cooler areas. As warm water becomes less dense and rises, it moves toward cooler areas. As the water moves away from the heat source, the water cools. Eventually this cool water will return to the warmer areas, where it is heated, and the cycle starts over again. You can expect the same types of convection currents you observed in the aquarium to occur in the oceans. To understand ocean currents, you need to consider another factor that you may not have thought about before. Most of the surface currents in the oceans are powered by surface winds that move water in the top 400 m (1300 ft) of the ocean. Global winds guide the surface winds, so in most areas ocean currents move in the same direction as global winds. Explore: How Does Water Move in Earth s Major Ocean Currents? You will be using what you now know about convection and winds to predict how water moves in Earth s major ocean currents. Then you will make a small poster showing your group s predictions. Procedure 1. Use what you know about the incoming energy from the Sun to decide where the oceans absorb the most solar energy and are warmest. Then decide where the oceans absorb the least solar energy and are coldest. Mark these areas on your Oceans page. 2. Start with currents in the North Atlantic Ocean, which is north of the Equator. Use what you know about global winds in this area (the westerlies and the trade winds) to decide where ocean currents will move west to east and where they will move east to west. Using a pencil, draw two arrows on your Oceans page to show your prediction of these ocean currents. 3. Global winds are high above Earth s surface and are not deflected by anything. However, ocean currents are deflected when they strike Earth s continents. Use what you know about the Coriolis effect to decide in which direction the currents will move when they are deflected by continents. Currents will move clockwise in the Northern Hemisphere. Draw two arrows on your Oceans page to show these ocean currents. Project-Based Inquiry Science WW 208

4. Use what you know about convection to decide where ocean waters in the North Atlantic will be cooling and where they will be heating up. Mark cooling next to one of the arrows you drew for currents. Mark heating next to another current arrow you drew. 5. Repeat Steps 2 4 for the South Atlantic, the North Pacific, the South Pacific, and the Indian Ocean. Currents in the Southern Hemisphere move in a counterclockwise direction. 6. On the chart on your Oceans page, record your predictions about the direction of ocean currents in the North Atlantic and the South Atlantic. Give reasons you made those predictions. 7. When you are finished, discuss your predictions with your group. Make a small poster showing the ocean currents you predicted. Record any disagreements your group had during discussions. Be prepared to report to the class how you made your predictions about the movements of Earth s ocean currents. You also need to be prepared to give the reasons for each prediction and any disagreements in your group. Communicate Share Your Prediction Share your predictions with the class. When it is your group s turn, hold up your poster, show the arrows representing the pathways of the ocean currents, and tell the class why you think the currents flow in those directions. Identify areas where water is cooling and areas where it is warming up. During your discussion, notice what the class agrees about and the disagreements you have. Discuss what else you need to know to resolve any disagreements. WW 209

Learning Set 4 What Other Factors Interact to Cause Weather Changes? Analyze Your Data The map below shows surface temperatures of ocean water in late spring. The map on the next page shows typical ocean currents. Use both maps to answer the questions below. Compare your predictions of the currents to the actual currents shown. This map shows surface temperatures of ocean water for one day in spring. Note that ocean temperature data are often reported in degrees Celsius, as on this map. 1. Compare your predictions for the North Atlantic to the map of actual ocean currents. You can ignore small details, such as whether your arrows are curved, or what you thought might happen in the Gulf of Mexico. Ignoring these details, which predictions match the actual fl ow of water? Which predictions are incorrect? 2. Compare your predictions about cooling and heating of ocean water in the North Atlantic to the map of actual ocean temperatures. Which predictions are correct? Which are incorrect? 3. For the rest of the Northern Hemisphere oceans, compare your predictions to the actual ocean currents. In what ways did your predictions differ from the actual currents? 4. For the Southern Hemisphere oceans, compare your predictions to the actual ocean currents. In what ways did your predictions differ from the actual currents? Project-Based Inquiry Science WW 210

Global currents include gyres large systems of ocean currents that circle clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. On this map, warm ocean currents are shown in red and cool ocean currents are shown in blue. Reflect 1. Look at 30 North latitude on the west side of the Atlantic (in Florida) and the east side of the Atlantic (in Africa). Why do you think the ocean water off the coast of Africa is cooler at this latitude than the water off the coast of Florida? (Hint: You can you use the fact that water has a high heat capacity, which means it takes water a long time to cool off and a long time to heat up.) 2. The ocean current that moves east across the North Atlantic also moves north. Why do you think this current does not move due east across the Atlantic? (Hint: Look again at the direction in which the westerlies blow.) WW 211

Learning Set 4 What Other Factors Interact to Cause Weather Changes? 3. North of Antarctica, there is an ocean current that completely circles around Earth in the same way that jet streams in the atmosphere circle around the planet. Why do you think there are no similar ocean currents in the Northern Hemisphere? 4. What else do you need to know to understand why Earth s ocean currents flow as they do? Effect of Oceans on Weather and Climate You can think of the oceans as a storehouse for solar energy. In fact, the oceans store most of the energy from the Sun that is available to heat Earth. To understand why, remember that Earth s oceans cover over 70 percent of its surface. That means the oceans absorb about three fourths of the solar energy that strikes Earth. In addition, water has a high heat capacity, which means it heats up slowly and it cools off slowly. Remember also that conduction transfers energy from areas at higher temperature to areas at lower temperature. During the day, water is usually at a lower temperature than surrounding land and air, so energy is transferred to the water. At night, water is often warmer than its surroundings, but energy is transferred away from the water slowly because water cools off slowly. Ocean currents play an important role in transferring thermal energy from one part of Earth to another. Because water cools slowly, ocean currents that carry water away from warm areas will transfer thermal energy across long distances. When ocean temperatures are warmer than air temperatures, the ocean heats the air above it and nearby land areas by conduction, convection, and radiation. Significant amounts of energy stored in the ocean can be carried inland by sea breezes. Project-Based Inquiry Science WW 212

The transfer of thermal energy by ocean currents affects regional climates. Ocean currents carry energy away from the Equator, and toward the North and South Poles. Landmasses near the currents receive more energy to warm the air than would be available from sunlight alone. The climate in these regions is warmer than in regions at the same latitude that do not receive this extra energy. In fact, Iceland receives more energy from ocean currents than it does from sunlight. However, ocean currents have a much greater effect on weather and climate when sea breezes are in the same direction as global winds. For example, a sea breeze in California is in the same direction as the global winds, from west to east. A sea breeze in Georgia will have less effect on the climate because as it blows from east to west, the sea breeze has to overcome the general west to east direction of the global winds in this area. Ocean water also moves in deep ocean currents. Water from the deep sea, where the water is very cold, can rise to the ocean surface. Places where this happens are called areas of upwelling. Upwelling often occurs when a deep ocean current collides with a landmass. Because the water from the deep ocean is cold, upwelling can cause the land nearby to be cooler than it would be otherwise. If you look at the temperature map of the United States, you will see that the coast of northern California is much cooler than regions farther inland. This cool climate is the result of upwelling combined with a cool surface current that flows to this region from the north. Explain Now that you know the oceans play an important role in transferring energy, you can answer this question: What is happening in the ocean and how does it affect weather and climate? Work with your group to develop a claim and explanation statement that answers this question. Begin by recording the question on a new Create Your Explanation page. Then work with your group to develop a claim about how oceans and ocean currents affect climate and weather patterns. Your claim can be very simple. It can simply list the factors that affect the fl ow of ocean currents and the effects ocean temperatures have on coastal land. WW 213

Learning Set 4 What Other Factors Interact to Cause Weather Changes? Then identify and record evidence from your explorations and from the maps that supports your claim and that will help you explain how those factors affect ocean currents and coastal land temperatures. Then record science knowledge you have about the ways in which ocean currents are formed, how they transfer energy around the planet, and how they affect coastal temperatures. You may want to use sketches to express some of your science knowledge. Work with your group to develop an explanation statement. Your statement should answer the question and provide reasons that the ocean currents flow as they do and affect weather and climate as they do. Make an Oceans poster showing your explanation. Include your claim, evidence, and science knowledge you have used. Use sketches showing ocean currents, and ocean and land temperatures to illustrate. Keep track of any disagreements in your group and what you still need to understand better to develop a more complete and accurate explanation. Communicate Share Your Explanation When it is your group s turn to share your explanation, show the class your poster. Report your claim, evidence, science knowledge, and explanation, using your sketches to help the class understand what you are reporting. Project-Based Inquiry Science WW 214

As each group shares its explanation, listen carefully. Notice any factors other groups include in their explanations that you may have left out. Notice any factors other groups might have left out. Listen to what each group tells you about the ways each factor affects ocean currents and land temperatures. If you do not understand something another group presents, or if you disagree, ask questions respectfully and offer suggestions. Revise Your Explanation As a class, discuss the strengths and weaknesses of the different explanations. Then create a class claim and explanation statement describing how oceans affect climate and weather. Update the Project Board In the What are we learning? column, record what you now know about what affects ocean currents, how ocean currents transport energy around the planet, and the effects of ocean currents on weather and climate. Be sure to record evidence for each of those entries in the What is our evidence? column. Record any questions you still might have about predicting weather in the What do we need to investigate? Column. What s the Point? Water covers over 70 percent of Earth s surface. Because water is efficient at absorbing energy from the Sun, the oceans act as a storage place for thermal energy. Ocean currents carry thermal energy away from the Equator toward the north and south. As this thermal energy is transferred by conduction, convection, and radiation it affects the climate and weather of places near the ocean currents. When a coastal area is near a warm ocean current, sea breezes will make the climate warmer than other places at the same latitude if the sea breezes are in the same direction as global winds. Cold ocean currents and upwelling can cause the climate and weather of nearby land to be cooler than other areas at similar latitudes. The large amount of water on Earth s surface makes it one of the most important factors in determining weather and climate. WW 215