In 1980 there was growing concern that the protective ozone layer over the Antarctic might be decreasing and thereby ...

Mehran January 4, 2017

@awashing let's take a closer look.

Some government officials have dismissed concerns that the protective ozone layer over the Antarctic might be decreasing by citing statistics that indicate that global atmospheric ozone levels remained constant.

Notice the issue with these statistics. The concern is that the protective ozone layer over Antarctic might be decreasing but they cite statistics on global atmospheric ozone levels.

This is a Weaken question so we are looking for an answer choice that weakens the relevance of the evidence cited by government officials.

(D) states, "quantities of atmospheric ozone shifted away from the polar caps, correspondingly increasing ozone levels in other regions."

This clearly undermines the relevance of the evidence cited by government officials by pointing out that the fact that global atmospheric ozone levels remaining constant is not inconsistent with deceasing ozone levels over Antarctic.

So (D) would be the correct answer.

Hope that helps! Please let us know if you have any other questions.

Julie-V July 17, 2019

How would we eliminate B as the wrong answer choice? I was stuck between B and D but ultimately chose B

Irina July 17, 2019

@Julie,

The conclusion relies on the fact that the global atmospheric ozone levels are representative of ultraviolet radiation that reaches the Antarctic, but just knowing the average ozone level globally tells us nothing about how ozone is distributed in the atmosphere. That is exactly what the correct answer choice D is getting at - ozone is concentrated in regions other than polar caps leaving the Antarctic vulnerable to solar radiation.

Now, let's look at (B). B says "decreases in the amount of atmospheric ozone over the Antarctic ice cap tend to be seasonal rather than constant:." B undermines the premise that "the ozone layers over the Antarctic might be decreasing" but the question asks us to undermine "the relevance of the evidence" NOT the premise. We are looking for a statement that would question government's reliance on the global atmospheric ozone levels statistic, and B fails to do that.

Let me know if this helps.