It is difficult to project the impact of climate change on volatility of food prices and use, but most models projecting the future indicate that prices will become more volatile. Some evidence suggests that droughts have been occurring more frequently because of global warming; and they are expected to become more frequent and intense in Africa, southern Europe, the Middle East, most of the Americas, Australia, and Southeast Asia. However, other research suggests that there has been little change in drought over the past 60 years. Their impacts are aggravated because of increased water demand, population growth, urban expansion, and environmental protection efforts in many areas. Droughts result in crop failures and the loss of pasture for livestock. A number of climate-related trends have been observed that affect water resources. These include changes in precipitation, the cryosphere and surface waters (e.g., changes in river flows). Observed and projected impacts of climate change on freshwater systems and their management are mainly due to changes in temperature, sea level and precipitation variability. Changes in temperature are correlated with variability in precipitation because the water cycle is reactive to temperature. Temperature increases change precipitation patterns. Excessive precipitation leads to excessive sediment deposition, nutrient pollution, and concentration of minerals in aquifers. The rising global temperature will cause sea level rise and will extend areas of salinization of groundwater and estuaries, resulting in a decrease in freshwater availability for humans and ecosystems in coastal areas. The rising sea level will push the salt gradient into freshwater deposits and will eventually pollute freshwater sources. The 2014 fifth IPCC assessment report concluded that:   Humans are exposed to climate change through changing weather patterns (temperature, precipitation, sea-level rise and more frequent extreme events) and indirectly through changes in water, air and food quality and changes in ecosystems, agriculture, industry and settlements and the economy. Air pollution, wildfires, and heat waves caused by global warming have significantly affected human health, and in 2007, the World Health Organization estimated 150,000 people were being killed by climate-change-related issues every year. A study by the World Health Organization concluded that climate change was responsible for 3% of diarrhoea, 3% of malaria, and 3.8% of dengue fever deaths worldwide in 2004. Total attributable mortality was about 0.2% of deaths in 2004; of these, 85% were child deaths. The effects of more frequent and extreme storms were excluded from this study. A 2014 study by the World Health Organization estimated the effect of climate change on human health. Not all of the effects of climate change were included in their estimates, for example, the effects of more frequent and extreme storms were excluded.