How so? His claim was that people will not be happier in warmer climates. I'm making a counterclaim to the contrary, that the experiencing self can be significantly happier(or at least feel significantly better) in climates where there is enough UV-radiation as opposed to those where there isn't like the Nordic countries and probably Alaska(in the case of the US).
It's meant to be an example from a broader class: the class of large life changes that, contrary to expectation, do not lead to increased happiness reports from the experiencing self. (In his specific example, you only get increased happiness reports by asking people to compare their current warmer life with their past colder life, thereby engaging the remembering self.)
In any event, if you're talking about seasonal affective disorder, it seems that dawn simulation works best, so it's related to visible light, not UV radiation.
People who have had a painful experience remember it as less painful if the pain tapers off, rather than cutting off sharply at the height of intensity, even if they experience more pain overall. I'd heard of this finding before (from Dan Ariely), but Kahneman uses the finding to throw the idea of "experiencing self" vs. "remembering self" into sharp relief. He then discusses the far-reaching implications of this dichotomy and our blindness to it.
The talk is entitled "The riddle of experience vs. memory".