It is a noticeable trend for writers and newscasters to say ‘further’ in the context of distance where one would expect the word ‘farther’ to be used. Is this a national or English-language-world etymological change of significance usage?
Not really. For physical distance, the correct word to use is farther. Easy to remember – far = physical distance. Further is in addition, figurative and metaphysical distance. To further a point. For example, Lem asks, “How much farther is it?” Clarke answers, “Ten light years. Any further questions, ask Robbie.”
Its usage can be ambiguous and in which case further is the safer option. However, it is wrong (technically) to say it is a further 10 miles to walk, or that the mountain is further away than you thought.
Apparently the misuse of further and the decline of farther has waxed and waned for centuries. In the future perhaps only further will be seen and heard but in the meantime most editors will keep their red pens busy. Vive la difference!