Contagion Annihilus

This bug was a nasty one. It turned people into plants. Some thought it was engineered by the Green psychoes. Everyone was forced to live inside bubbles, or they'd turn into pumpkins or god knows what. It created a disturbing trade in human/plant farming. The massive drop in global CO2 resulting from 8 billion trees suddenly appearing was catastrophic. That's when climate change really hit the fan.