In their Nature paper, Root and her colleagues analyzed 143 scientific studies involving a total of 1,473 species of animals and plants. Each study found a direct correlation between global warming and biological change somewhere in the world. For example, several studies revealed that, as temperatures increased in recent decades, certain species began breeding and migrating earlier than expected. Other studies found that the geographical range of numerous species had shifted poleward or moved to a higher elevation -- indicating that some plants and animals are occupying areas that were previously too cold for survival.
Were these biological and behavioral changes isolated events, or did they reflect a worldwide pattern consistent with global warming? After exhaustive statistical analyses of all 143 studies, Root and her co-authors concluded that global warming is, in fact, having a significant impact on animal and plant populations around the world.