The ACT Science Section features passages of science information, usually containing a chart or graph, which are followed by 5-7 questions.
Below, you can test your own ACT science abilities with a quiz. The quiz is equivalent to one set of questions from the ACT Science test. There will be an answer key after the quiz and the answer explanations after you reviewed your answers yourself.
ACT Science Quiz Passage
Global warming caused by human activity seems to correlate strongly with loss of glacier mass. Figure 1 shows a steady increase in average global surface temperature due to human activity, starting in 1950 and continuing through 2,000. Figure 1 also compares two predictive models for changes in global surface temperature during that time period: one model that only accounts for natural forces, and one that accounts for both natural and human impacts on global surface temperatures. You can see the accuracy of these two models in relation actual observed changes in global surface temperature.
Figure 2 shows changes in glacier mass, as measured in meters of thickness, from 1955 to 2010. This data comes from three glaciers that have been identified by the United States Geological Survey (USGS) as “benchmark” glaciers. USGS scientists have determined that these glaciers show melting rates and loss of ice that are typical of glaciers around the world. The changes in mass are indicated by values for cumulative mass balance (CMB). A positive value indicates that a glacier is gaining mass. negative values show that a glacier is melting and losing mass. Glacial mass is expressed by the thickness of the glacier, in meters.
Assume that as average surface air temperatures go up and become warmer, glacier mass decreases from melting ice. On the basis of Figure 1 and Figure 2, what time period did the region surrounding Wolverine Glacier experience a significantly different pattern of changes in surface temperature, compared to the global pattern of surface temperature change at that time?
A) 1960 – 1965
B) 1970 – 1975
C) 1985 – 1990
D) 1995 – 2000
South Cascade Glacier is located at a latitude farther south than the other two glaciers in Figure 2. If latitude accounts for the difference between Cascade Glacier’s rate of melt compared to the other two glaciers, one can conclude that glaciers in lower southern latitudes:
E) melt at a faster rate than glaciers located in higher northern latitudes.
F) melt at a less predictable rate than glaciers located in higher northern latitudes.
G) are less directly influenced by global climate change than glaciers located in higher. northern latitudes
H) lose mass at roughly the same rate as glaciers located in higher northern latitudes.
On the basis of the information given in Figure 1, one can conclude that, prior to 1950:
A) models that used natural forces alone were the strongest predictor of changes to observed global surface temperature.
B) observed temperatures were consistent with models that used both natural and human forces.
C) there were no years where models based on natural forces alone correctly predicted observed temperatures.
D) observed temperatures were sometimes inconsistent with predictive models.
Assume that over time, proximity to human populations causes the greatest cumulative loss of mass in glaciers. Based on this information and the data provided, which of the following predictions about Gulkana Glacier would most likely be true, if the human population surrounding Gulkana increases by 25% between 2015 and 2020, while the human populations around the other two glaciers remain unchanged?
E) The values for Gulkana and Wolverine Glacier’s cumulative mass balance will become closer by 2020.
F) The values for Gulkana and South Cascade Glacier’s cumulative mass balance will become closer by 2020.
G) By 2020, the value for Gulkana Glacier’s cumulative mass balance will become closer to the values for Wolverine Glacier, but farther from the values for South Cascade Glacier.
H) By 2020, the value for Gulkana Glacier’s cumulative mass balance will become closer to the values for both Wolverine Glacier and South Cascade Glacier.
In what year did Gulkana Glacier change from having positive cumulative mass balance to negative cumulative mass balance?
D) This change is not shown in the figure.
So how’d you do? If you got any of these answers wrong, look carefully at the question, the passage, and the figures. Try to figure out exactly why you missed the answers. I recommend that you read the next section after that, in which I’ll explain the logic behind each correct answer, and give you some tips on how the wrong answers in this question set can be avoided.
ACT Quiz Answer Explanations
Question 1 Answer
According to Figure 1, average global surface air temperatures rose steadily between 1950 and 2000, with little or no temperature decreases. And the question states that a rise in surface air temperatures causes glaciers to lose mass. This means that Wolverine Glacier would lose mass continuously between 1955 and 2000, provided the surface air temperatures around it followed the exact same pattern as global surface air temperatures.
However, between 1985 and 1990, you can see Wolverine Glacier showing a positive cumulative mass balance. This means that its mass actually increased. This is a sign that air surface temperatures around Wolverine Glacier became colder during that period, contrary to the global trend toward warmer surface temperatures at the time. So answer (A), 1985-1990 is the only answer that matches the data on the two charts.
Question 2 Answer
(E) is correct because South Cascade Glacier, which is located farther south than Gulkana or Wolverine Glaciers, consistently shows a lower negative cumulative mass balance than the other two glaciers. This means that Cascade Glacier is losing mass — which is to say melting — at a faster rate than the other two glaciers.
South Cascade Glacier is melting at steady, predictable rate, much like Gulkana Glacier. So that eliminates answer (F). South Cascade also seems to be influenced by climate change as much or more than either of the other two glaciers, since it shows the greatest amount of melting in relation to the steady increase in average global temperatures seen in Figure 1; this means (G) can’t be correct. Finally, South Cascade Glacier is obviously not melting at the exact same rate as the other two glaciers because its rate of change in cumulative mass balance is distinctly separate from the other two glaciers in Figure 2. So we can eliminate (H) as well.
Question 3 Answer
(A) isn’t correct because prior to 1950, both prediction models on the chart forecast almost the exact same temperatures. So one model is not clearly a stronger predictor than the other. (B) isn’t correct because the highest observed temperatures before 1950 were not consistent with either of the two models. (C) is wrong because Figure 1 shows a point before 1950 where the observed temperature clearly overlaps with predictions made based on natural forces alone.
This leaves us with (D). (D) has to be correct because it is the opposite of (B); if answer (B) is incorrect, (D) must be right!
Question 4 Answer
For this question, you need to recognize the pattern in Figure 1. To get the answer, look at the general direction that the lines are going in as each glacier’s melt progresses in time. Imagine where the lines will go next if things stay roughly the same as they are in 2015… and imagine where Gulkana Glacier’s line (and its melt rate/cumulative mass balance represented by its line) will go if there is a 25% increase in the human population around Gulkana.
Since South Cascade and Wolverine Glaciers will not have any changes in their surrounding population, their lines will keep moving downward at the same angle as before. But Gulkana Glacier’s line will start going down more sharply, showing much more loss of mass through melting. Why? Because Gulkana will be getting a human population increase, and more people means a faster rate of melt.
Gulkana Glacier’s cumulative mass balance will start to drop more quickly, reaching larger negative numbers. This means its value will get farther away from the value for Wolverine Glacier, which is above Gulkana Glacier on the chart. Conversely, South Cascade Glacier’s melt rate is beneath Gulkana on the chart, with lower negative values. So as Gulkana loses mass more quickly, its line will get closer to South Cascade’s line on the chart. (F) is the only answer that reflects this. All other answer choices either bring Gulkana closer to Wolverine or push it farther from South Cascade.
Question 5 Answer
This is almost a trick question. The ACT Science Section will sometimes ask you for an answer that isn’t actually available!
1963 is the year that South Cascade Glacier went from increasing in mass with a positive cumulative mass balance to decreasing and having negative CMB values. 1989 is the year Wolverine Glacier went from positive to negative, and 1982 is actually the year that Wolverine Glacier went in the opposite direction — from losing mass to gaining it. There is no point anywhere on the chart where Gulkana is actually increasing in mass, so there can’t be a point where Gulkana changes direction from increase to decrease. So the answer is (D).