For years, the focus on the world's response to climate change has been on nation states, which have been mostly unsuccessful in brokering comprehensive agreements or taking action. Cities, by contrast, are preparing risk assessments, setting greenhouse-gas emission reduction targets, and pledging to act.
Marine and continental records show an abrupt negative shift in carbon isotope values at ~55.8?Myr ago. This carbon isotope excursion (CIE) is consistent with the release of a massive amount of isotopically light carbon into the atmosphere and was associated with a dramatic rise in global temperatures termed the Palaeocene–Eocene thermal maximum (PETM).
To persist, species are expected to shift their geographical ranges polewards or to higher elevations as the Earth’s climate warms. However, although many species’ ranges have shifted in historical times, many others have not, or have shifted only at the high-latitude or high-elevation limits, leading to range expansions rather than contractions.
More than half of the solar energy absorbed by land surfaces is currently used to evaporate water. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate.
