There are two approaches to identifying the climax of a work: (1) it is the moment of highest emotion and intensity; (2) it is the moment that forces the inevitable ultimate decisions, those that inevitably lead to the resolution. My preference is to use the second definition because decisions are more definitive than emotionality (emotional scenes are variably dependable because a character's emotions can go awry and lead astray--as with Torvald's--thus can be variably indicative of final climactic moments).
In A Doll's House, the climax comes when Nora realizes what Torvald actually is, that he is not the loving husband she thought he was. Ibsen embeds this climactic realization in the drama by prescribing it in his stage directions: "[[Nora] looks steadily at him ... with a growing look of coldness in her face.]"
Nora was convinced that in his unstinting love of her, Torvald would wonderfully want to take all the responsibility for her act of forgery once he understood that she had acted to save his life, because of this conviction she haltingly says to Mrs. Linde, "if it should happen that there were some one who wanted to take all the responsibility, all the blame, ... A wonderful thing is going to happen!" While in this quotation she is hinting at an act of suicide to counter her act of forgery, she is also expressing her belief that Torvald will selflessly want to protect her and shoulder all the blame and infamy himself. Torvald ironically reinforces this idea when he says, just before reading Krogstad's letter, that he wished occasion might arise where he could give his life for her safety: "I have often wished that you might be threatened by some great danger, so that I might risk my life's blood, and everything, for your sake." Again ironically, his remark gives Nora the strength to face him, and she tells him to read the letter.
Helmer. [Puts his arms round her.] ... Do you know, Nora, I have often wished that you might be threatened by some great danger, so that I might risk my life's blood, and everything, for your sake.
Nora [disengages herself, and says firmly and decidedly]. Now you must read your letters, Torvald.
Torvald reacts to what he reads with rage, fear and strings of invective and with utter denunciation and rejection of Nora. Torvald's tirade is the turning point leading to the climax, which occurs in the midst of his assault when Nora slowly comes to understand in truth what sort of man Torvald is and what she can in truth expect from him. Nora even tells us that now she understands, and even Torvald elicits a confirmation of her new understanding from her, although he speaks while unwitting of her climactic epiphany.
Helmer. No tragic airs, please. [Locks the hall door.] Here you shall stay and give me an explanation. Do you understand what you have done? Answer me! Do you understand what you have done?
Nora [looks steadily at him and says with a growing look of coldness in her face]. Yes, now I am beginning to understand thoroughly.
Helmer. And I have to thank you for all this--you whom I have cherished during the whole of our married life. Do you understand now what it is you have done for me?
Nora [coldly and quietly]. Yes.
By the "inevitable ultimate decision" view of climax identification, the point of highest emotion (gone awry and leading Torvald astray) is the turning point while Nora's cold, silent epiphany of revelation is the climax: it is the climactic moment when the progress of the denouement and the resolution are irreversibly decided. After seeing the truth about Torvald, after realizing the lie undergirding her marriage, Nora can never make any decision but to reject Torvald: the epiphanic climax has sealed the outcome of the drama.
Helmer. ... We will only shout with joy, and keep saying, "It's all over! It's all over!" Listen to me, Nora. You don't seem to realise that it is all over. What is this?--such a cold, set face!
The climax of A Doll's House is in Act III, shortly after the party, and takes place after Torvald realizes that one of his best friends, Dr. Rank, has shut himself away to die.
Torvald seems genuinely affected by his friend's impending death, and reading the letter from Krogstad distresses him completely. Upon reading about the debt that Nora took on, Torvald instantly grows angry and stops his wife from leaving the house as she was starting to do. Idealistically, Nora thinks that Torvald will take the blame for her forgery and intends to commit suicide to free Torvald from her guilt.
"Nora. Let me go. You shall not suffer for my sake. You shall not take it upon yourself.
Helmer. No tragedy airs, please. (Locks the hall door.) Here you shall stay and give me an explanation."
Nora begins to understand that Torvald is not nearly as noble as she thought he was. Nora has complete faith in her past actions and feels no guilt for doing what was necessary, but only for how it is affecting her husband. However, when she realizes that Torvald hates her for her crime, Nora understands that her husband does not truly love her, does not respect her, and will disavow her for saving his life.
Torvald insists that they must capitulate to Krogstad's wishes and hthat he will no longer allow her to raise their children because she is immoral and a liar. Before he can continue, a new letter arrives from Krogstad saying that he no longer has any intention of blackmailing them.
Torvald's emotions instantly change and he begins to rejoice and is no longer angry with her. He begins to act she'd never be injured by such harsh and cruel words and starts talking to her lovingly again. He forgives her and says that her actions were because of "womanly helplessness," nothing more.
Nora says very little to him, only that she is "beginning to understand thoroughly"; she changes out of her party dress, then tells him to sit down. She begins to tell him that they have never understood each other during their marriage and that he has wronged her terribly. This conversation, about how little Torvald respects her and how unhappy she is, leads to Nora announcing her choice to leave Torvald for good (her decision was already made well before and that is why she changed into her day clothes, ready to walk right out the door).
The climax of any story is often thought to be a point near the end of the story when the tension, or crisis, is at its highest. The most stressful and important part of A Doll's House is when Torvald reads the letter leading Nora to finally realize how manipulated her marriage is.
The climax of the play would be when Nora decides to leave her husband Torvald and their children behind. This appears to be the highest moment of tension and emotion in the play. Everything up until this point builds the tension until the reader knows that Nora will be making a very important decision. It is only towards the very end that we know what that decision is. She has had enough of Torvald's complete disregard of her importance to the household and to him and their children.