In situations characterised by armed conflict and climate change, can informal institutions resolve conflict around shrinking resources? It is widely acknowledged that low state capacity increases the likelihood of violence in the context of climate change. In such context, informal institutions should play a crucial role in preventing and mitigating violence in the absence of formal institutions. However, little is known of the characteristics of these informal institutions and existing literature on climate change and conflict has examined them in isolation from national contexts and actors. This paper seeks to address this gap and argues that impartiality is essential for the ability of informal institutions to resolve resource-based conflict, a by-product of climate change, and prevent violence escalation. However, when institutions are partial, because of co-option by the state or other external actors, their decisions may further increase communal violence and prolong civil conflict. Partial institutions can encourage people to take justice into their own hands, and push individuals to join rebel groups offering more favourable options in redressing grievances. This theoretical argument is explored through a case study on central Mali, where partial informal institutions, in conjunction with other factors, have led to increased violence in the region.