In psychology, the heat hypothesis states that above average daily temperatures (e.g. uncomfortably hot days above 90˚F) increase aggressive motives and behavior. [1]

A notable researching on this subject is American psychologist Craig Anderson, who, since 1995, has done a meta-analysis of all publications on the subject. Anderson notes correlations as common as a greater tendency of baseball pictures to hit a batter with a ball on hot days or increases of horn honking on hot days by drivers without air conditioning to more extreme statistics such as a probable increase of 12,000 murders per year per every 1˚F increase in average temperature, via global warming. [2]

Human thermodynamics
In human thermodynamic terms, the heat hypothesis phenomenon would seem to find explanation in Boerhaave’s law, i.e. that inputs of heat to a system, correlative with system temperature increase (except at phase change), cause volume expansion. In the gas phase, according to Boltzmann-Planck logic, such expansion is said to correlated to increase in disorder or chaos in the system. In non gas phase systems, volume increase will commensurate with transition phase bond breaking and structure reformation to follow. In the case of society, the same effects invariably must occur, albeit via human chemical bond breakages or dissolutions and expansion of volumes of interactions of people viewed as molecules (human molecules) attached to substrate. [3]

In short, increases in murders on hot days can be explained as a system’s way of increasing volume. The study of how a volume of human molecules change with temperature, e.g. such as when a city comes alive with people bustling about on the first warm day, following cold winter, with people expanding out in to the countryside, etc., however, is complex subject. [4]

It would seem intuitive that a correlate of a prolonged increase or spike in murder rates in a particular area, for instance, would be a migration out of ground zero of the disruptive area and subsequently a decrease in disruptive area density would result. Murder capitals of the world, on average, tend towards population decreases. This logic applied to a generalized murder increase, correlative with temperature increase, then would likewise result in similar outward expansions and thus substrate volume increase in alignment with Boerhaave’s law.

References
1. Anderson, Craig A., Bushman, Brad J., Ralph W. Groom (1997). “Hot Years and Serious and Deadly Assault: Empirical Tests of the Heat Hypothesis.” Journal of Personality and Social Psychology, Vol. 73, pgs. 1213-23.
2. Blumberg, Mark S. (2002). Body Heat: Temperature and Life on Earth (pgs. 157-58). Harvard University Press.
3. (a) Thims, Libb. (2007). Human Chemistry (Volume One), (preview), (Google books). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two), (preview), (Google books). Morrisville, NC: LuLu.
4. Thims, Libb. (2008). The Human Molecule, (preview). Morrisville, NC: LuLu.