Jeff Oliver

The western monarch's latest population count revealed a 99.9% decline since the 1980s.

Butterfly declines over recent decades are often linked to stressors like habitat loss, invasive species or pesticides.

But new research in the journal Science suggests human-induced climate change might play a bigger role than once thought.

Based on observations at 70 locations in the western U.S., researchers found a 1.6% drop in butterfly populations each year between 1977 and 2018.

Those losses coincided with autumn warming, possibly because heat worsens physiological stresses on developing insects and host plants, or lets natural enemies stay active longer.

Warmer and wetter summers showed positive population effects, undercut by the fact the West has been drying over recent decades.

The findings suggest butterfly conservation is a multifaceted problem and might benefit from new tactics focused on groups of species and shared habitats.