The phrase “is what one would expect” indicates that the melting of the Arctic Ice is a possible explanation for the unusual weather experienced by the UK.
A – Wrong
It is not the only explanation. It is a possible explanation. The word “only” is too strong.
B – Wrong
We cannot infer that if the ice was not melting the unusual weather would not have been present.
C – Wrong
‘Must’ is too strong and hence this is wrong.
D – Correct
The word “could” suggests that the melting of Arctic ice is a possible explanation and hence this is the correct answer.