Van Lange et al. propose a plausible model of climatic and particularly temperature effects on behavior that they call CLASH: CLimate, Aggression, and Self-Control in Humans. According to the model, the greater propensity to aggression and violence of people near the equator is the result of a (1) slower life-history strategy, (2) greater focus on and orientation toward the future, and (3) greater self-control. The model seems plausible given the data presented. There are a few puzzles in the model, at least for me, such as the limitation of the model to the Northern Hemisphere (why would the Southern Hemisphere be different?) and the apparent near discounting of cultural variables, for which a strong case has been made by Nisbett and Cohen (1996), among others. But the greatest puzzle in the model is its rather strange conjoining of three variables that are presented as distinct, but that, I suspect, would be highly correlated and likely unifactorial were data collected to test their statistical properties. To focus more on the future and especially the distant future, one needs greater self-control (e.g., Mischel, Reference Mischel2015). And a slower life history strategy really is, in large part, a focus on the future because one perceives oneself as having the intelligence to navigate life so that one has a relatively remote future on which to focus.

The question then arises as to whether a more parsimonious interpretation of the data might be possible – an interpretation that views the probably high intercorrelations of these variables (were data actually to be collected) as reflecting some kind of single underlying factor. I would like to suggest what this factor might be, namely, intelligence, which can be viewed narrowly in terms of traditional factors (Carroll Reference Carroll1993) or broadly in terms of successful intelligence, encompassing creative, analytical, practical, and wisdom-based aspects (Sternberg Reference Sternberg2003b).

There already is evidence that, on average, people from cooler climates show higher analytical intelligence than people from hotter climates (Lynn & Vanhanen Reference Lynn and Vanhanen2002). One possible explanation, among many, derives from the distinction between intelligence as a trait and intelligence as a state (Sternberg Reference Sternberg2014).

It is well known that a number of factors can affect people's performance on assessments of intelligence (Anastasi & Urbina Reference Anastasi and Urbina1997). The effects of these factors are not limited to formal intelligence or related tests, but can be found in everyday life as well. For example, people welcome air conditioning, not only because it makes them more comfortable, but also because the temperatures it produces enable them to work more effectively (Sepaenen et al. Reference Sepaenen, Fisk and Lei2006), in the same way that freedom from unwanted distractions does. Indeed, extreme heat is an unwanted distraction from one's work. Extreme heat, like extreme noise or extreme lack of ventilation, can adversely affect cognitive and other performance. These are among the many variables that contribute to the distinction between one's intellectual competence and one's intellectual performance (see Davidson & Sternberg Reference Davidson, Sternberg, Neimark, de Lisi and Newman1985; Sternberg Reference Sternberg2015). Intelligence as a state – as a level of performance distinct from and potentially lower than one's intelligence as a trait (competence) – could be responsible for the differences that Van Lange et al. have observed.

Intelligence may be a more parsimonious interpretation of the data, but is it plausible that it would predict the kinds of behavior Van Lange et al. have reviewed, such as aggressive and violent behavior? There are persuasive data that IQ, an aspect of intelligence, does predict such variables. More intelligent people plan more for the future, have better self-control, and have a slower life history, in part because their higher intelligence allows them to live longer (Deary & Whalley Reference Deary and Whalley2008; Gottfredson & Deary Reference Gottfredson and Deary2004). They are less likely to be incarcerated or, in general, to put themselves in a position where they will die from violence, caused either by themselves or by others. Indeed, in studies of styles of conflict resolution, my collaborators and I found that the style most associated with higher intelligence was “step-down,” or trying peacefully to defuse conflicts (Sternberg & Dobson Reference Sternberg and Dobson1987; Sternberg & Soriano Reference Sternberg and Soriano1984).

In sum, the variables posited by CLASH may be three related manifestations of intelligence rather than three distinct constructs. In the end, the only way to determine the correct explanation would have to be empirical. And by the way, regardless of the explanation – Van Lange et al.'s, mine, or someone else's – climate change bodes ill for the rational behavior in the future of our citizens and their leaders.