Editing IPCC:AR6/SROCC/Chapter-5 (section)

==== 5.4.2.1 Human Health and Environmental Health ====

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===== 5.4.2.1.1 Water-borne diseases =====

SR15 concluded that climate change will result in an aerial expansion and increased risk of water-borne disease with regional differences ( ''high to very high confidence'' )(Hoegh-Guldberg et al., 2018). AR5 concluded that warming, excessive nutrient and seawater inundation due to SLR are projected to exacerbate the expansion and threat of cholera (Pörtner et al., 2014) ( ''medium confidence'' ). This assessment focuses on health risks caused by ''Vibrio'' bacteria and HABs. ''Vibrio cholerae'' (causing cholera) is estimated to be responsible for around 760,000 and 650,000 cases of human illness and death respectively in the world in 2010 (Kirk et al., 2015). An assessment of HABs is given in Box 5.4.

''Vibrio'' species naturally occur in warm, nutrient-rich and low salinity coastal waters. Since AR5, analysis of the the Continuous Plankton Recorder dataset (Section 5.2.3) has shown a significant increase in ''Vibrio'' abundance in the North Sea over the period 1958‒2011 related to sea surface warming (Vezzulli et al., 2016). Other time series data have confirmed a poleward expansion of ''Vibrio'' pathogens in mid- to high-latitude regions, ascribed at least partly to climate change (Baker-Austin et al., 2013; Baker-Austin et al., 2017). Extreme weather events such as flooding and tropical cyclones are also linked to increased incidences of ''Vibrio'' -related disease, suggested to be caused by the increased exposure of human populations to the pathogens during these extreme events (Baker-Austin et al., 2017). New evidence since AR5 therefore increases support for the linkages between warming, extreme weather events and increased risk of diseases caused by ''Vibrio'' bacteria ( ''very'' ''high confidence'' ).

Extrapolating from the observed relationship between environmental conditions and current ''Vibrio'' distributions, coastal areas that experience future warming, changes in precipitation and increases in nutrient inputs can be expected to see an increase in prevalence of ''Vibrio'' pathogens. These effects have been simulated in a global-scale model that relates occurrences of ''Vibrio'' with SST, pH, dissolved oxygen and chlorophyll ''a'' concentration under the SRES B1 scenario (Escobar et al., 2015). In the Baltic Sea, a nearly two-fold increase in the area suitable for ''Vibrio'' is projected between 2015 and 2050 for both RCP4.5 and RCP8.5 scenarios (relating to projected SST increase of 4°C‒5°C), resulting in an elevated risk of ''Vibrio'' infections (Semenza et al., 2017). Projected conditions of increased coastal flooding from storm surges and SLR (Section 5.2.2) will also increase exposure to waterborne disease (Ashbolt, 2019), such as ''Vibrio'' ( ''medium confidence'' ). However, uncertainty in the socioeconomic factors affecting the future vulnerabilities of human populations render quantitative projections of the magnitude of health impacts uncertain (Lloyd et al., 2016).

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