There has long been a concern that global warming would cause species movements reflective of the instinctive drive to seek the most favorable environmental conditions. One concern is that agricultural pests and carriers of diseases like malaria would move north and south from tropical and subtropical areas. Some changes may benefit the species but not necessarily humankind. Both predicted and observed changes are discussed with examples from plant and animal species. Some concerns are controversial, kike the effect of climate change on polar bears.