The Earth has been gradually warming over at least the last 500 years, with the trend accelerating markedly during the 20th century, according to a new study published in the journal Nature, based on temperature data from underground rocks. Since 1500, the Earth’s temperature has increased by about one degree Celsius, with half that increase occurring in the last 100 years, researchers found. In an accompanying article in Nature, Jonathan Overpeck of the University of Arizona writes that human-caused climate change is likely the source of the warming, and that continued warming can be expected. A separate study in the new issue of the Proceedings of the National Academy of Sciences indicates that climate change may be disrupting the migration and hibernation patterns of animals and birds.