Editing IPCC:AR6/WGII/Chapter-2 (section)

==== 2.5.1.4 Changing Risks of Diseases ====

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Multiple studies predict increases in disease incidence or geographic and phenological changes of pathogens, vectors and reservoir host species due to climate change with or without other non-climatic variables ( [[#González--2010|González et al., 2010]] ; [[#Moo-Llanes--2013|Moo-Llanes et al., 2013]] ; [[#Roy-Dufresne--2013|Roy-Dufresne et al., 2013]] ; [[#Liu-Helmersson--2014|Liu-Helmersson et al., 2014]] ; [[#Laporta--2015|Laporta et al., 2015]] ; [[#Ryan--2015|Ryan et al., 2015]] ; [[#Haydock--2016|Haydock et al., 2016]] ; [[#Hoover--2016|Hoover and Barker, 2016]] ; [[#Prist--2017|Prist et al., 2017]] ; [[#Blum--2018|Blum and Hotez, 2018]] ; [[#Dumic--2018|Dumic and Severnini, 2018]] ; [[#Hundessa--2018|Hundessa et al., 2018]] ; [[#Ryan--2019|Ryan et al., 2019]] ; [[#Ryan--2021|Ryan et al., 2021]] ). However, models predicting changes in infectious disease risk are complex and sometimes produce conflicting results and lack consensus ( [[#Caminade--2014|Caminade et al., 2014]] ; [[#Giesen--2020|Giesen et al., 2020]] ). For example, malaria is projected to increase in some regions of Africa, Asia and South America by the end of the 21st century if public health interventions are not sufficient, but is also forecasted to decrease in some higher-risk areas (Cross-Chapter Box Illness in this chapter) ( [[#Peterson--2009|Peterson, 2009]] ; [[#Caminade--2014|Caminade et al., 2014]] ; [[#Ryan--2015|Ryan et al., 2015]] ; [[#Khormi--2016|Khormi and Kumar, 2016]] ; [[#Leedale--2016|Leedale et al., 2016]] ; [[#Murdock--2016|Murdock et al., 2016]] ; [[#Endo--2020|Endo and Eltahir, 2020]] ; [[#Mordecai--2020|Mordecai et al., 2020]] ).

While malaria risk is predicted to decrease in some lowland tropical areas as temperatures become too hot for vector or parasite development, other warm-adapted diseases, like dengue and Zika, transmitted by ''A. aegypti'' , are predicted to increase (Cross-Chapter Box Illness in this chapter, chapter 7) ( [[#Ryan--2019|Ryan et al., 2019]] ; [[#Ryan--2021|Ryan et al., 2021]] ). In more temperate regions, arboviruses and other VBDs with wider thermal breadths, such as West Nile fever, Ross River fever and Lyme disease, are predicted to increase with climate warming ( [[#Ogden--2008|Ogden et al., 2008]] ; [[#Leighton--2012|Leighton et al., 2012]] ; [[#Shocket--2018|Shocket et al., 2018]] ; [[#Shocket--2020|Shocket et al., 2020]] ; [[#Couper--2021|Couper et al., 2021]] ). Drought can exacerbate these effects of temperature ( [[#Paull--2017|Paull et al., 2017]] ).

A global analysis of 7346 wildlife populations and 2021 host–parasite combinations found that organisms adapted to cool and mild climates are likely to experience increased risks of outbreaks along with climate warming, while warm-adapted organisms may experience a lower disease risk, providing further support for predictions that climate change will increase the transmission of infectious diseases at higher latitudes across a taxonomically diverse array of pathogens ( ''robust evidence'' , ''high agreement'' ) ( [[#Cohen--2020|Cohen et al., 2020]] ). A study examining the future risk of arboviruses (chikungunya, dengue, yellow fever and Zika viruses) spread by ''A. aegypti'' and ''A. albopictus'' projected increased disease risk due to interactions of multiple variables, including increased human connectivity, urbanisation and climate change ( [[#Kraemer--2019|Kraemer et al., 2019]] ), although vector species’ ranges will broaden only slightly ( [[#Campbell--2015|Campbell et al., 2015]] ).

In sum, climate change is expected to expand and redistribute the burden of vector-borne and other environmentally transmitted diseases of wild animals, domesticated animals and humans, by shifting many regions toward the thermal optima of VBD transmission for multiple parasites, thereby increasing risk of transmission, while pushing temperatures above optimal and towards upper thermal limits for other vectors and pathogens, thus decreasing their transmission ''(high confidence)'' (see also chapter 7) ( [[#Mordecai--2019|Mordecai et al., 2019]] ; [[#Mordecai--2020|Mordecai et al., 2020]] ). These effects are mediated by other human impacts such as LUC, mobility, socioeconomic conditions and vector and pathogen control measures ( [[#Parham--2015|Parham et al., 2015]] ; [[#Tjaden--2018|Tjaden et al., 2018]] ).

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