Climate Change Threatens Monarchs

The eastern monarch population, known for its spectacular migration to Mexico, has plummeted by over 80% since the mid-1990s. The western population, which overwinters in coastal California, has seen an even more drastic decline of over 95% since the 1980s. This butterfly's migration is a multi-generational relay. The generation that flies south to Mexico can live up to nine months, but it takes three to four subsequent, shorter-lived generations to complete the journey back north. This intricate cycle depends on the precise timing of milkweed availability along the route. Warmer autumns are failing to trigger the monarchs' instinct to migrate south, delaying their departure by as much as six weeks. This delay means many butterflies encounter lethal cold temperatures in the Midwest before reaching their overwintering grounds. The high-altitude oyamel fir forests in Mexico provide a crucial microclimate for the overwintering monarchs, protecting them from extreme temperatures and preserving their energy. These forests are themselves threatened by a warming and drying climate, which could render them unsuitable for the butterflies within decades. Extreme weather events, intensified by climate change, pose another severe threat. A single storm in 2002 killed an estimated 80% of the overwintering population in Mexico, a catastrophic loss from which the population has struggled to recover. In December 2024, the U.S. Fish and Wildlife Service proposed listing the monarch butterfly as a threatened species under the Endangered Species Act. This follows a 2023 decision by Canada to list the monarch as endangered and Mexico's long-standing legal protection of the Monarch Butterfly Biosphere Reserve. Conservation efforts focus on restoring milkweed and nectar plant habitats across North America. Organizations are working with agricultural producers to plant these vital resources on private lands, which form the core of the monarch's migration route and breeding habitat.