Health
Climate change poses a wide range of risks to population health – risks that will increase in future decades, often to critical levels, if global climate change continues on its current trajectory (McMichael et al. 2003). The three main categories of health risks include (i) direct‐acting effects (e.g. due to heat waves, amplified air pollution, and physical weather disasters), (ii) impacts mediated via climate‐related changes in ecological systems and relationships (e.g. crop yields, mosquito ecology, marine productivity), and (iii) the more diffuse (indirect) consequences relating to impoverishment, displacement, resource conflicts (e.g. water), and post‐disaster mental health problems.
Extreme Weather Events
This trend toward more variability and fluctuation is perhaps more important, in terms of its impact on human health, than that of a gradual and long‐term trend toward higher average temperature (Epstein 2002). Infectious disease often accompanies extreme weather events, such as floods, earthquakes, and drought. These local epidemics occur due to loss of infrastructure, such as hospitals and sanitation services, but also because of changes in local ecology and environment.
Environment
Climate change may dramatically impact habitat loss, for example, arid conditions may cause the deforestation of rainforests, as has occurred in the past (Sahney et al. 2010b).
Temperature
A sustained wet‐bulb temperature exceeding 35 °C is a threshold at which the resilience of human systems is no longer able to adequately cool the skin. A study by NOAA from 2013 concluded that heat stress will reduce labor capacity considerably under current emissions scenarios (Dunne et al. 2013). There is evidence to show that high temperatures can increase mortality rates among fetuses and children. Although the main focus is often on the health impacts and risks of higher temperatures, it should be remembered that they also reduce learning and worker productivity, which can impact a country’s economy and development.
Water
The freshwater resources that humans rely on are highly sensitive to variations in weather and climate. In 2007, the IPCC reported with high confidence that climate change has a net negative impact on water resources and freshwater ecosystems in all regions. The IPCC also found with very high confidence that arid and semiarid areas are particularly exposed to freshwater impacts (Kundzewicz et al. 2007).
As the climate warms, it changes the nature of global rainfall, evaporation, snow, stream flow, and other factors that affect water supply and quality. Specific impacts include the following:
- Warmer water temperatures affect water quality and accelerate water pollution (Miller 2007).
- Sea‐level rise is projected to increase saltwater intrusion into groundwater in some regions. This reduces the amount of freshwater available for drinking and farming (Miller 2007; USEPA 2015).
- In some areas, shrinking glaciers and snow deposits threaten the water supply. Areas that depend on melted water runoff will likely see that runoff depleted, with less flow in the late summer and spring peaks occurring earlier (Miller 2007). This can affect the ability to irrigate crops. (This situation is particularly acute for irrigation in South America, for irrigation and drinking supplies in Central Asia, and for hydropower in Norway, the Alps, and the Pacific Northwest of North America.)
- Increased extreme weather means more water falls on hardened ground unable to absorb it, leading to flash floods instead of a replenishment of soil moisture or groundwater levels.
- Increased evaporation will reduce the effectiveness of reservoirs.
- At the same time, human demand for water will grow for the purposes of cooling and hydration.
Social Effects of Extreme Weather
As the World Meteorological Organization explains, “recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.” Pielke et al. (2008) normalized mainland US hurricane damage from 1900 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 has the second most damage among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane, with $157 billion of normalized damage (Pielke et al. 2008).
The American Insurance Journal predicted that “catastrophe losses should be expected to double roughly every 10 years because of increases in construction costs, increases in the number of structures and changes in their characteristics.” The Association of British Insurers (ABI) has stated that limiting carbon emissions would avoid 80% of the projected additional annual cost of tropical cyclones by the 2080s. The cost is also increasing partly because of building in exposed areas such as coasts and floodplains. The ABI claims that reduction of the vulnerability to some inevitable effects of climate change, for example through more resilient buildings and improved flood defenses, could also result in considerable cost‐savings in the long term (ABI 2005).
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