Title: 2. How has climate changed? | Australian Academy of Science
Headings: 2. How has climate changed?
2. How has climate changed?
Past climate has varied enormously on a variety of time-scales
Past records demonstrate that global climate is sensitive to small but persistent influences
Box 2.1: How do we detect climate change?
Box 2.2: Has climate warming recently stopped?
Global average temperatures have increased over the past century
Changes are evident in many parts of the climate system
There are regional differences to climate change including within Australia

Content: The thickness of the ice has also decreased by more than 30% over the last 30 years. In the Southern Ocean, there are strong regional differences in the changes to areas covered by sea ice, but a small increase in total coverage, driven by shifts in winds and ocean currents in a warming Southern Ocean. Strengthening circumpolar winds around Antarctica have also been linked in part to thinning of the ozone layer. The amount of water vapour in the atmosphere has increased since the 1980s, which is consistent with warmer air ( Box 1.3 ). The surface of the ocean in rainy parts of the world is becoming less salty, which is consistent with freshwater dilution from increased rainfall. Some ocean currents have changed in response to changes in surface winds, ocean temperature and ocean saltiness. The changes include a southward shift of the Antarctic Circumpolar Current and increasing southward penetration of the East Australian Current. An increasing number of plants and animals, on land and in the oceans, are undergoing shifts in their distribution and lifecycles that are consistent with observed temperature changes. There are regional differences to climate change including within