ACT Science Test

ACT Science Test Sample

1 pt

DIRECTIONS: There are seven passages in this test. Each passage is followed by several questions. After reading a passage, choose the best answer to each question. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.

Passage I

The climate system is formed by the interactions between the atmosphere, oceans, land, ice, and biosphere. Climate systems are affected by feedbacks within the system. A climate feedback is any change that causes a secondary (or indirect) change to occur within the climate system. When the change is in the same direction, it is a positive feedback; if the change acts in the opposite direction, it is a negative feedback. Many scientists believe that carbon dioxide emissions from human activity may be causing global temperatures to rise faster than they would naturally. Putting more carbon dioxide into the atmosphere changes the Earth’s equilibrium, but the net effect on climate remains unclear. Two theories presented below address different feedback loop scenarios.

Theory 1

As atmospheric temperatures rise, sea surface temperatures also rise with a corresponding decrease in sea ice extent. As sea ice and glaciers melt, more solar radiation is absorbed by the ocean and land surfaces, further increasing surface temperatures. In addition, the oceans are a natural carbon sink, removing carbon dioxide from the atmosphere. But as oceans warm, they will not be able to store as much carbon dioxide. Warmer oceans will experience greater evaporation rates, putting larger amounts of water vapor in the atmosphere. More atmospheric carbon dioxide and water vapor will absorb more radiation from the Earth’s surface and emit more radiation back, amplifying global warming.

Theory 2

Increasing the concentration of carbon dioxide in the atmosphere will further raise global temperatures. Air near the surface will warm and enhance evaporation rates over land and water. Greater evaporation rates will increase the amount of water vapor in the atmosphere. Greater moisture content in the atmosphere combined with increased thermal energy will enhance the development of clouds, particularly of low- and mid-level clouds. Clouds absorb and reflect solar radiation, depending on the cloud’s physical characteristics. Low-level clouds have a greater cooling capacity than mid- and high- level clouds. An increase in low-level cloud thickness would cool the surface of the land and ocean and mitigate the effects of warming by atmospheric gases.

1. According to Theory 1, which of the following most affects an ocean’s ability to store carbon dioxide?

1 pt

The table below lists different types of clouds and the average altitude at which they generally form. Use the table to answer the question.

According to Theory 2, which type of cloud would have the greatest cooling effect on climate?

1 pt

Melting sea ice changes the cooling capacity of the surface of the oceans. Water absorbs more solar radiation than ice. As sea ice melts, the absorption of solar radiation increases, raising sea surface temperatures and evaporation rates. Which theory do these statements support?

1 pt

Which theory suggests a negative climate feedback scenario?

1 pt

A study will be conducted to test the probability of these future climate scenarios. Which of the following topics would be most important to study to determine the likelihood of Theory 2?

1 pt

A "runaway greenhouse effect" occurs when a planet absorbs more energy from the Sun than it can radiate back to space. The hotter the temperatures become, the faster the planet warms up. In which theory would a runaway greenhouse effect most likely occur?