Species have evolved to live and thrive in certain habitats. If the climate is changing enough to alter ecosystems, we expect to see species responding by changing where they live or the timing of important temperature-dependent biological events. Species’ responses such as shifting ranges or earlier blooming and hatching may be the best evidence that climate is actually changing; it is unlikely that these temperature-dependent events would change in this way if the planet were not getting warmer.

Jim Toomey/AGE fotostock
Altrendo Nature/Thinkstock
Patrick Palmen/Hollandse Hoogte/Redux
Bill Draker/ImageBroker/Getty Images
Lars Howlett/Aurora Photos
© jack thomas/Alamy