Humans fight over many things, including mates, money, ideas, religion, and natural resources. A recent study by Hsiang and colleagues asks how climate change might affect the frequency of human conflict.
The authors performed a meta-analysis using data from 60 published studies that examined how climate affected human conflict across different contexts. They found striking patterns: for each standard deviation increase in temperature or change in rainfall (producing either more rain and floods or more droughts), inter-personal violence rises by 4%, and inter-group conflict rises by 14%. These increases in conflict can be caused by a host of factors that may be related, including changes in agricultural production, water availability, institutional infrastructure, and political stability. If climate change predictions are correct (i.e. temperatures increase by 2 to 4 standard deviations during the 21st century) and the general patterns discovered by Hsiang and colleagues are accurate, then conflict between individual humans and groups of humans could rise dramatically.
Hsiang S, M Burke, E Miguel (2013) Quantifying the influence of climate on human conflict. Science:10.1126/science.1235367