उपर्युक्त परिच्छेद से, निम्नलिखित में से कौन-सा सार्थिक निष्कर्ष सत्य होता है?

Correct Option: Climate change poses a threat to the survival of polar bears.

The passage highlights that summer ice melting is occurring earlier and faster due to warming, declining by 30% in three decades. It specifically mentions that the "lengthening period of summer melt threatens to undermine the whole Arctic food web, atop which stand polar bears." Since polar bears are at the top of this endangered food web, their survival is directly threatened by these climate change-induced changes. Option A is incorrect because the passage suggests the summer melt period is lengthening (making summer effects longer, not shorter). Option B is highly impractical and not mentioned. Option C is incorrect because food chains are threatened, but the passage does not claim they will completely disappear solely due to polar bears' absence. Hence, Option D is the most crucial message.