All famines are caused by natural disasters. What makes them political is that people die when their ability to overcome natural disasters is restricted or removed.

E.g. for the Irish Famine, the natural disaster was the outbreak of the phytophthora infestans disease affecting potato crops - the outbreak spread from North America across Europe, affecting Belgium, Netherlands, France & the UK. The cause of death in Ireland was the English exporting all food produced in Ireland that wasn't potatoes. An interestingly relevant historical record here is the Australian Convict Collection showing the number of Irish convicts sent to Australia & Tasmania for stealing food during the famine years.