Guillemots are birds of Arctic regions

[BTGmoderatorDC]

Guillemots are birds of Arctic regions. They feed on fish that gather beneath thin sheets of floating ice, and they nest on
nearby land. Guillemots need 80 consecutive snow-free days in a year to raise their chicks, so until average temperatures
in the Arctic began to rise recently, the guillemots' range was limited to the southernmost Arctic coast. Therefore, if the
warming continues, the guillemots' range will probably be enlarged by being extended northward along the coast.

Which of the following, if true, most seriously weakens the argument?

(A) Even if the warming trend continues, there will still be years in which guillemot chicks are killed by an unusually
early snow.
(B) If the Arctic warming continues, guillemots' current predators are likely to succeed in extending their own range
farther north.
(C) Guillemots nest in coastal areas, where temperatures are generally higher than in inland areas.
(D) If the Arctic warming continues, much of the thin ice in the southern Arctic will disappear.
(E) The fish that guillemots eat are currently preyed on by a wider variety of predators in the southernmost Arctic
regions than they are farther north.

Why isn't Option D the correct Option? Can some experts explain?

OA D

[DavidG@VeritasPrep]

Guillemots are birds of Arctic regions. They feed on fish that gather beneath thin sheets of floating ice, and they nest on
nearby land. Guillemots need 80 consecutive snow-free days in a year to raise their chicks, so until average temperatures
in the Arctic began to rise recently, the guillemots' range was limited to the southernmost Arctic coast. Therefore, if the
warming continues, the guillemots' range will probably be enlarged by being extended northward along the coast.

Which of the following, if true, most seriously weakens the argument?

(A) Even if the warming trend continues, there will still be years in which guillemot chicks are killed by an unusually
early snow.
(B) If the Arctic warming continues, guillemots' current predators are likely to succeed in extending their own range
farther north.
(C) Guillemots nest in coastal areas, where temperatures are generally higher than in inland areas.
(D) If the Arctic warming continues, much of the thin ice in the southern Arctic will disappear.
(E) The fish that guillemots eat are currently preyed on by a wider variety of predators in the southernmost Arctic
regions than they are farther north.

Why isn't Option D the correct Option? Can some experts explain?

OA D

Conclusion: If warming continues, guillemots' range will be enlarged.
Premises: Guillemots feed on fish beneath frozen ice
Need 80-consecutive snow-free days to raise chicks; range previously limited to Southern Arctic

We're trying to weaken the conclusion that the guillemots' range will increase. Notice there are really only two relevant premises. First, they need 80 consecutive free days to raise their chicks. Well, we know that if warming increases, they're likely to see a greater range of locations in which they'll see this happen. So, logically, the best way to weaken this conclusion would be to show that the other premise will be negatively impacted by warming. This is what D gives us.

The guillemots get their food beneath ice. If the ice melts in the Southern Arctic, the guillemots will have to move if they want to eat. Thus, while warming may allow them to live in more northern regions, if the southern regions where the guillemots once resided are no longer inhabitable, their overall range will not increase.