As the ozone layer in the Earth's upper atmosphere thins, it allows more ultra-
0 k% R( T- \) a9 z! d6 |violet radiation from space to pass through the upper atmosphere. Thus, since
% Y3 B/ O; Z. ~/ Ythe ozone layer recently started to thin over North America, the upcoming mea-
+ s1 Z! A3 l6 B- O' gsurement of ultraviolet radiation over North America should show that ultraviolet 8 ]6 y/ X3 C8 N6 @% j' Z
radiation has increased in intensity at ground level there. \" W+ x, \3 B: W" E
Which of the following, if true, most seriously weakens the argument given? 0 A' _9 r) o `. j" W) ?
The ozone layer in the Earth's upper atmosphere has thinned to a much
9 u6 x y" u1 ?! } greater extent over the Earth's southern pole than it has over North
7 m& _9 h* Z; F9 }2 c$ E: d2 w America.
8 h+ _# R9 R1 t0 S During the next decade, the countries of North America will completely halt 0 @3 u6 c% S% [
production of the chemicals that cause the ozone layer to thin. 7 o( ]7 Y7 A" Q& B7 L8 L* _, H, W
Clouds absorb ultraviolet radiation, and cloud cover has been increasing . w1 Q+ L: ?( |. A; g
over North America in recent years because of changing weather patterns. ) c2 j0 Z5 X* q+ Q7 k2 J
The instruments that are used to measure ultraviolet radiation near the Earth's
7 |+ v! F6 `1 ~6 [ surface have not become significantly more accurate in recent years. ; n1 K' ?! d7 i5 y: A
At any given time, ultraviolet radiation is typically more intense on mountain -; P: V% m6 f" O n- ]
tops than at low-lying plains. |