Hi Martian Tom,
Welcome to the forums. We don't get many Martians here, and even fewer poets so you're even more welcome.
It's probably worth laying out a few fundamentals about how copyright works. It protects human expression of ideas in the disciplines of literature (prose or poetry), music, drama and art. There is separate protection for more collaborative activities such as sound recordings and films but that need not concern us here. The important distinction is that copyright doesn't protect the underlying idea itself, just the specific expression of it. The expression needs to be original in the sense that it is created in the mind of the author and is thus an expression of his or her character. Much of what we value in the work of other people can form part of our own expression, often subconsciously. For this reason, the rigid law - thou shalt not copy someone else's work - is softened by some useful exceptions, for instance for the purpose of our own private study, for quotation and for making pastiches or parodies. These exceptions are in a category named
fair dealing, and 'fair' means that the extent of any copying must be no more than a fair and reasonable person would say was necessary for the purpose.
So taking that last example category, it is legally acceptable to choose a poem which others would recognise as the work of another author, and employing the same style, make a parody, caricature or pastiche of it, so long as the re-worked version contains sufficient originality on the part of the second author. Where parody etc is concerned, there is no need to explicitly acknowledge the work on which it is based, since clearly the audience is expected recognise this without much prompting. However where verbatim quotation is used, the source must be cited where this is practical. Quotation is most useful in the context of literary criticism or review, where it can be employed to show how the first author expressed a particular idea, when mere paraphrase would not suffice.
So with all that in mind, your poem can use another person's idea or structure so long as the new poem flows from your own creativity. You can even quote within your poem (without necessarily acknowledging it is a quote) provided that the quotation is justified by the overall purpose of your poem. For this you need to examine why you want/need to copy this stanza verbatim. If it is by way of a homage or hat-tip to George Carlin, then that is justifiable per se, but if you poem has an air of pastiche or parody, then using the 12 word stanza becomes even more justifiable. Ultimately though it comes down to the reasonable person test, when deciding whether the amount of Carlin's work which has been appropriated is fair dealing.
All of the foregoing explains how the law in the UK works. In the USA they operate a slightly different doctrine of exceptions known as fair use. Judging whether something is fair use under their system involves evaluating the new work under four headings. This is explained in more detail
in this Wikipedia article. It is only necessary to note here that the US approach emphasizes the economic impact of the new work on the old, whereas in the UK that is never more than a minor consideration.
In my introduction I used the word 'human' deliberately. With the rise of AI generated written works, this issue takes on a whole new dimension. By definition AI machines are trained on other people's work and deliberately set out to copy the style of a particular person if that is what is prompted. But the output of the AI has yet to be recognised as worthy of copyright in its own right, because under the current doctrine 'originality' can only come from a human person's creativity. UK law currently allows copyright to be granted to the person who makes the arrangements leading to the creation of the computer-generated work* (see
section 9(3) of the Copyright Designs and Patents Act 1988) but it is debateable how long this particular piece of law will remain in place, given that no other jurisdiction currently allows copyright in the case of wholly computer-generated works. Since I doubt that any AI machine so far developed has any concept of 'fairness', it is probable that in future we will see cases where an AI generated work will fail to meet the fair dealing standards, and the human who claims the copyright in the new work will be found liable for infringement caused by the AI.
*
This change to the law occurred well before the rise in AI and was intended to apply to the use of software such as Photoshop or Blender etc, where the human user is very much in control of the way in which the software creates the output. We have already seen test cases about whether AI can be deemed an inventor for the purposes of patents, so it is only a matter of time before section 9(3) is challenged in court with respect to copyright for AI generated works.
