There is growing evidence that climate change, particularly increasing temperatures, is already having significant impacts on the world’s physical, biological and human systems, and it is expected that these impacts will become more severe.
Warmer temperatures are causing changes in the hydrological cycle at regional and global scales, including decreases in the amount of water stored as ice in most of the world’s glaciers, ice sheets and sea ice; decreasing snow cover and earlier snow melt; and changes in rainfall patterns. These changes affect the incidence and severity of drought and floods and the availability of water, which in turn present challenges for many aspects of human society and industry (e.g. agriculture, rural economies, insurance, water security and food security). Sea level rise due to losses from ice stores and thermal expansion is another consequence of climate change that will have an increasing impact on human settlements and infrastructure.
Increasing temperatures also affect biological systems. There is evidence of shifts in the range of plant and animal species to higher latitudes and altitudes, changes in species composition and abundance, and changes in the timing of many life-cycle events such as flowering and migration. Changes such as these will affect many of our managed ecosystems (particularly agriculture and forestry) and biodiversity.
Many of these impacts, especially when combined, are likely to cause increasing pressure on our resources and industries, and possibly on our social systems and health. The pages in this section discuss the environmental, economic, social, and security impacts of climate change, in the context of human society and values.
Climate change influences on biological and physical systems from a biophysical perspective are discussed in ‘The climate is changing’. These include sea level rise, changes in ice mass, changes in ocean circulation and rainfall patterns, ocean warming and acidification, species migration, and aridity.