A little more information on the opening word of Genesis 8.22 (‛ôd ):
The Hebrew adverb ‛ôd has been rendered with the idea of a: going-around, continuance, still, again, yet, while, as long as, during, etc.
It has two primary categories of meaning relating to action: continuing or durative action, and repeated or additional action. Other nuances of the word derive from one of these two primary semantic roles.
The NASB, a literal translation, renders the term mostly as: "again" (nearly 100x); "still" (84); "longer", "any longer" (nearly 100x), "yet (43x); "more" (39x), and in numerous other ways in lesser representations. So anyone can see from this that there is no one word to cover all that can be expressed with ‛ôd.
‛ôd can also be negated with the addition of a negative particle 'ayin or lō', (which appears at the beginning of Gen. 8.22). At Isaiah 2.4, the negative particle lō' appears with ‛ôd (Literally: "and-not they-will-learn more war": NASB, "Never again will they learn war.")
Other examples: Gen. 8.21; 9.15; Lev. 27.20; Num. 18.22; Deut. 3.26; Ecc.9.6)
At Gen. 9.15, we read: "and never again will the waters become a flood to destroy all flesh." The statement does not exclude another world-wide judgment. Does it?
Now we can better understand why Fox translated Gen. 8.22 thus: "22 (never) again, all the days of the earth, shall sowing and harvest, cold and heat, summer and winter, day and night ever cease!" (Parenthesis his.)
Hence, the Hebrew word at the beginning of the verse (in the presence of the negative particle in the full statement) may serve as an adverbial expression modifying the whole sentence. The NW translators of the Revised edition employed it as such at the beginning of the verse, affecting the whole statement. It does not mean that their selection of words or the sum of them was the best translation choice, but perhaps they saw a chance here to prop their doctrinal belief of an ever-lasting earth.
Even the translation choice of "while" used in some versions (NASB, etc. -- suggesting the earth is perishable) -- reflects the interpretation of the translators. How so? Well, the Hebrew word ôd appears nearly 500x in the Hebrew text, yet less than 10x is it rendered "while" in NASB -- Gen. 8.22 being one of the few places where it appears. Obviously, the NASB translators don't believe the earth is ever-lasting. Do they?
Someone may conclude that their choice of words must implicate the earth is forever, eternal. However, the adverbial expression, "from now on" excludes the inherent notion of eternity or creation of the earth up to the point of the spoken declaration. Actually, biblical context shows the earth was created. (Gen. 1.1) It wasn't forever there. Nor should the verse be used as proof that the earth shall endure forever. Whether the earth is ever-lasting or not must be gathered from other Scriptural sources.
The main point is that, "As long as the earth remains, there will be planting and harvest, cold and heat, summer and winter, day and night." (NLT)
Through clever use of words, translators at times indulge in interpreting certain passages to their own belief. The NWTr may have done so here, but other translators don't hesitate to do alike in other places (like using "while" in Gen. 8.22, "hell" for both "hades" and "tartarus" in their versions-2 Pet 2.4), or by adding "personality" to "spirit of God" at Genesis 1.2.
So basically, at Gen. 8.22, God promised that the daily and annual cycles of nature would continue for as long as the earth remained. I think the rest is added interpretation to God's declaration.
