Evaluation of the global water cycle's response to current and future drivers of climate change [Chapter 4.3]

A key component of the climate system is the global water cycle. The complex interactions between the land-ocean-atmosphere are inherently linked through the water cycle. The global water cycle is known to influence global atmospheric circulations by controlling the global energy cycle through latent heat exchanges associated with evaporation and cloud condensation and also the carbon, nutrient and sediment cycles. Changes to this balance has far reaching climatic effects, especially considering that over the past century human activities have altered not only the land surface but also the atmospheric composition (Stute et al. 2001; Karl and Trenberth 2003). A change to the atmospheres’ composition is the primary way that humans have altered the natural flow of energy through the global climate (Karl and Trenberth 2003). That temperatures are increasing globally is unequivocal, as reported in the fourth assessment report of the Intergovernmental Panel for Climate Change. (IPCC 2007). Observations in recent decades of air and ocean temperatures show the climate system is warming, with hot days, hot nights and heat waves becoming more frequent in the past 50 years (IPCC 2007). One direct consequence of a warmer world is an increase in water vapour contained in the atmosphere, indeed for every one decree increase in temperature there is a seven percent increase in the water vapour content of the atmosphere (Karl and Trenberth 2003). Accordingly the water cycle will be altered and the key processes of precipitation, evaporation, river discharge are expected to change.