The Role of the Ocean in Controlling Climate

Paragraph 1：To predict what the climate will be like in the future, scientists must rely on sophisticated computer models. These models use mathematical equations to represent physical processes and interactions in the atmosphere, ocean, and on land. A starting point is usually based on current measurements or estimates of past conditions. Then, using a spherical grid laid out over the entire globe, thousands of calculations are performed at grid intersections to represent and assess how conditions in the air, in the sea, and on land will change over time. Because of their complexity and size, supercomputers are used to run full-scale climate models. Much of the uncertainty in their outputs comes from the way that various aspects of the climate are represented by different models, and even more so, because there are aspects of climate that are not well understood, one of which is how the ocean impacts climate. 

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1. According to paragraph 1, the results of full-scale climate models are questionable in part because 

O the supercomputers used for such modeling are large and complex 

O thousands of calculations have to be performed to assess conditions 

O past conditions cannot always be estimated accurately 

O there are multiple ways to represent the same aspect of climate

Paragraph 2：The ocean’s role in global warming stems principally from its huge capacity to absorb carbon dioxide and to store and transport heat. In the sea, photosynthesis by marine plants and algae, especially phytoplankton, removes great quantities of carbon dioxide from the atmosphere. Hence, the greater the growth (productivity) of phytoplankton in the sea, the greater the removal of carbon dioxide. But what controls the ocean’s productivity? There are several limiting factors, but results from a recent experiment suggest that in areas of the ocean where other nutrients are plentiful, iron may be one of the most important and, until recently, unrecognized variables controlling phytoplankton production. Some have proposed a radical, highly controversial, and uncertain means to counteract global warming: adding iron to the oceans to induce phytoplankton blooms. Perhaps increased phytoplankton growth would use up a significant amount of carbon dioxide in the atmosphere, but perhaps not, and there might well be side effects that could be detrimental to the ocean ecosystem. 

2. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage  Incorrect choices change the meaning in important ways or leave out essential information. 

O Iron may be one of the most important factors in controlling phytoplankton production in ocean waters that are rich in other nutrients.

O Results from a recent experiment suggest that several factors limiting phytoplankton production in ocean waters have gone unrecognized. 

O Although it was not recognized until recently, nutrients are plentiful in areas of the ocean where iron controls phytoplankton production. 

O Until recently, the importance of iron was not taken into account in experiments concerning phytoplankton production. 

3. According to paragraph 2, how might increasing phytoplankton growth help lower global temperatures？ 

O By cooling the oceans 

O By decreasing carbon dioxide levels in the ocean 

O By reducing the amount of carbon dioxide in the atmosphere

O By transporting heat from the ocean’s surface to deeper levels 

Paragraph 3：Within the ocean, the production of limestone, in the form of calcium carbonate skeletons or shells, also reduces atmospheric carbon dioxide. However, when deposits of limestone become exposed and weathered on land or are recycled in the sea, carbon dioxide is released back into the atmosphere. What is not well understood is how much carbon dioxide resides in the sea and at what rate it is taken up and recycled. Relatively new research has also discovered beneath the sea a new and potentially significant threat to skyrocketing Earth temperatures: gas hydrates. Gas hydrates are a solid, crystalline form of water, like ice, except that they contain additional gas, typically methane, and are often found stored in ocean sediments. Increased ocean temperatures could cause gas hydrates to dissociate, releasing massive amounts of methane gas into the atmosphere and cause undersea landslides in the process. Consequently, hydrates may, if released, significantly increase global warming as well as create a geologic hazard to offshore drilling operations. 

4. According to paragraph 3, which of the following reduces atmospheric carbon dioxide  

O The weathering of limestone 

O The production of limestone

O The recycling of carbon dioxide 

O The presence of methane in gas hydrates 

5. According to paragraph 3, why are gas hydrates a possible threat to the global climate？ 

O If disturbed by offshore drilling, they can destroy limestone deposits. 

O They can replace regular ice at certain locations. 

O If melted, they may release a lot of carbon dioxide into the atmosphere. 

O They contain a lot of methane, which may be released as the ocean warms.

Paragraph 4：The ocean is also a great reservoir and transporter of heat. Heat from the ocean warms the atmosphere and fuels tropical storms. Heat is transported by currents from the equator to the poles. Ocean circulation is strongly controlled by wind and by the sea’s balance of salt and heat. Scientists think that climate warming may slow down circulation, while cooling may speed it up, but these responses are not well understood. Evaporation from the ocean also supplies the precipitation that creates fields of snow and ice at high latitudes. Snow and ice coverage change the reflectivity of Earth’s surface and are an important influence on how much incoming radiation is either absorbed or reflected. Furthermore, clouds and water vapor in the atmosphere come mainly from the sea and strongly influence climate. Surprisingly, clouds are one of the least understood and most poorly modeled parts of the climate change equation. Most climate modeling grids fail to take into account common-sized cloud formations. Aerosols, tiny particles of soot, dust, and other materials, are thought to seed cloud formation, scatter incoming radiation and promote cooling, but this effect, which would counteract warming, is also only superficially understood. Computer models of climate change must take into account all of the processes within the ocean, over land, and in the sky that potentially influence warming. No wonder there is such uncertainty. 

6. Which of the following is NOT mentioned in paragraph 4 as a way in which the ocean affects the climate？ 

O It stores heat. 

O It moves heat from the equator toward the poles. 

O It speeds up wind circulation.

O It warms up the atmosphere. 

7. Paragraph 4 suggests that a significant decrease in snow and ice fields at high latitudes would have what effect？ 

O More clouds and water vapor would be produced in the atmosphere. 

O More of the Sun’s radiation would be absorbed by Earth.

O The oceans would cool more quickly. 

O More precipitation would occur at low latitudes. 

8. Why does the author mention that Most climate modeling grids fail to take into account common-sized cloud formations？ 

O To suggest why the influence of clouds on climate change is still undetermined

O To explain why research on climate change does not focus on clouds 

O To help explain why it is unclear whether aerosols have the effect of counteracting warming 

O To explain in part why scientists are uncertain how much incoming radiation is absorbed or reflected 

Paragraph 3：Within the ocean, the production of limestone, in the form of calcium carbonate skeletons or shells, also reduces atmospheric carbon dioxide. ■However, when deposits of limestone become exposed and weathered on land or are recycled in the sea, carbon dioxide is released back into the atmosphere. ■What is not well understood is how much carbon dioxide resides in the sea and at what rate it is taken up and recycled. ■Relatively new research has also discovered beneath the sea a new and potentially significant threat to skyrocketing Earth temperatures: gas hydrates. ■Gas hydrates are a solid, crystalline form of water, like ice, except that they contain additional gas, typically methane, and are often found stored in ocean sediments. Increased ocean temperatures could cause gas hydrates to dissociate, releasing massive amounts of methane gas into the atmosphere and cause undersea landslides in the process. Consequently, hydrates may, if released, significantly increase global warming as well as create a geologic hazard to offshore drilling operations. 

9. Look at the four squares that indicate where the following sentence could be added to the passage.  

Nor is carbon dioxide the only gaseous substance in the ocean that may affect climate. 

Where would the sentence best fit  Click on a square to add the sentence to the passage.  

10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selected THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong. To review the passage, click on View Text .  

Answer Choices 

O Estimates of future conditions are entered into supercomputers to calculate climate possibilities at various places on Earth. 

O The ocean’s capacity to absorb carbon dioxide remains great despite recent reductions of marine plant nutrients such as iron. 

O Oceans absorb a great deal of carbon dioxide from the air through limestone production and the photosynthesis of phytoplankton.

O Ocean circulation is strongly controlled by wind and by the sea’s balance of salt and heat. 

O Gases are stored in the sea in the form of shells and hydrates, but gases stored in these ways can be recycled to the atmosphere where they may cause warming.

O The ocean holds and moves a great deal of heat, and as ocean water evaporates, it produces clouds, snow, and ice, which all affect global temperatures.