Wildfires in the western United States and hurricanes on the East Coast captured media attention this summer and fall. But throughout 2018, weather events also had devastating humanitarian consequences in developing countries, from immense floods in the Indian state of Kerala to an intense drought in Afghanistan that affected millions.

Over the past decade, academics and policymakers have vigorously debated the question of whether climate change poses a security threat, with particular emphasis on whether it causes internal conflict. Connections are complex, leaving policymakers to talk about climate change vaguely as a “threat multiplier” when combined with other forces. But saying that climate change is a threat multiplier isn’t all that helpful unless we know something about the characteristics that make countries more likely to experience instability.

In fact, several risk factors make some countries more vulnerable than others to the consequences of climate change. Three stand out in particular: