Predicting species’ responses to climate change is especially challenging for migratory species, like monarchs, because they could respond to climate change in two fundamentally different ways. First, because they depend on diverse resources across a vast landscape, and because the timing of migration is driven by environmental cues, migratory species could be especially vulnerable to environmental changes. On the other hand, their propensity to move could buffer them against shifting resources, with the outcome being little net change to their population sizes and distributions. Monarchs’ response to climate change will also be driven by how milkweed responds; even if temperatures allow monarch survival, if conditions cause their milkweed host plants to go dormant, become too dry, or die altogether, monarchs will need to move to other areas.
Climate change models suggest that monarchs will need to move northward from their current range in June and July, and then return southward in August to track the conditions they currently use for reproduction. Currently, only the spring generation appears to move northward before laying eggs, so this would represent a change from their current migratory pattern.Climate models also predict that the overwintering grounds in Mexico may soon no longer be suitable for monarchs, indicating that the eastern North American monarch population may require different overwintering habitat. Whether monarchs can successfully overwinter in other areas depends in part upon their being able to survive the colder temperatures and different habitats present in areas such as the southern U.S.
To minimize the impacts of climate change, it is important to maintain corridors of suitable monarch and milkweed habitat, and ensure that other pressures on their populations are minimized.
A climate vulnterability report for monarchs is available on the WWF website here.