Monarch butterflies are now facing a new threat: Rising atmospheric carbon dioxide levels that kill off the medicinal properties of their main food source. That’s according to a recent study out of the University of Michigan that is co-authored by a Stanford University researcher. Higher levels of carbon dioxide reduce the medicinal properties of a milkweed species, leading to the butterfly’s reduced ability to tolerate parasites. This study comes out as the monarch butterfly populations have seen sharp declines in recent decades.
