Effects of climate change on humans
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Climate change has brought about severe and possibly permanent alterations to our planets’ geological, biological and ecological systems. The Intergovernmental Panel on Climate Change (IPCC) now contends that “there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities”. These changes have led to the emergence of large-scale environmental hazards to human health, such as ozone depletion, loss of biodiversity, stresses to food-producing systems and the global spread of infectious diseases. The World Health Organization (WHO) estimates that 160,000 deaths, since 1950, are directly attributable to climate change. Many believe this to be a conservative estimate.
To date a neglected aspect of the climate change debate, much less research has been conducted on the impacts of climate change on health, food supply, economic growth, migration, security, societal change, and public goods, such as drinking water, than on the geophysical changes related to global warming. Human impacts can be both negative and positive. Climatic changes in Siberia, for instance, are expected to improve food production and local economic activity, at least in the short to medium term. Numerous studies suggest, however, that the current and future impacts of climate change on human society are and will continue to be overwhelmingly negative.
The majority of the adverse effects of climate change are experienced by poor and low-income communities around the world, who have much higher levels of vulnerability to environmental determinants of health, wealth and other factors, and much lower levels of capacity available for coping with environmental change. A report on the global human impact of climate change published by the Global Humanitarian Forum in 2009, including drawing on work done by the World Health Organization earlier in that decade, indicated that developing countries suffer 99% of the casualties attributable to climate change. This also raises questions of climate justice, since the 50 least developed countries of the world account for not more than 1% of worldwide emissions of greenhouse gases that cause global warming.
Since so little research has been conducted into the human impacts of climate change and because of the difficulty in differentiating the influence of climate change from other contributing factors, statistics relating to the human impact of climate change carry significant margins of uncertainty.[clarification needed] Particularly on a global level, much of the statistical data on the human impact of climate change should only be considered as being indicative of the order of magnitude of impact.[clarification needed]
Though there has been inadequate research (and policy-related discussion) on the human impacta of climate change, a number of organizations are raising the profile of this issue by organizing various high-level meetings and publishing reports on the topic. Such organizations include Oxfam, the United Nations Development Programme, the United Nations Environment Programme, the World Health Organization, the Office of the High Commissioner for Human Rights, the United Nations High Commissioner for Refugees (UNHCR), the Office for the Coordination of Humanitarian Affairs, the Global Humanitarian Forum, Care International, Greenpeace, Maplecroft, the World Bank, and the International Federation of Red Cross and Red Crescent Societies.
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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. 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.
Climate change thus threatens to slow, halt or reverse international progress towards reducing child under-nutrition, deaths from diarrheal diseases and the spread of other infectious diseases. Climate change acts predominantly by exacerbating the existing, often enormous, health problems, especially in the poorer parts of the world. Current variations in weather conditions already have many adverse impacts on the health of poor people in developing nations, and these too are likely to be 'multiplied' by the added stresses of climate change.
A changing climate thus affects the prerequisites of population health: clean air and water, sufficient food, natural constraints on infectious disease agents, and the adequacy and security of shelter. A warmer and more variable climate leads to higher levels of some air pollutants and more frequent extreme weather events. It increases the rates and ranges of transmission of infectious diseases through unclean water and contaminated food, and by affecting vector organisms (such as mosquitoes) and intermediate or reservoir host species that harbour the infectious agent (such as cattle, bats and rodents). Changes in temperature, rainfall and seasonality compromise agricultural production in many regions, including some of the least developed countries, thus jeopardising child health and growth and the overall health and functional capacity of adults. As warming proceeds, the severity (and perhaps frequency) of weather-related disasters will increase - and appears to have done so in a number of regions of the world over the past several decades.[when?] Therefore, in summary, global warming, together with resultant changes in food and water supplies, can indirectly cause increases in a range of adverse health outcomes, including malnutrition, diarrhea, injuries, cardiovascular and respiratory diseases, and water-borne and insect-transmitted diseases.
Health equity and climate change have a major impact on human health and quality of life, and are interlinked in a number of ways. The report of the WHO Commission on Social Determinants of Health points out that disadvantaged communities are likely to shoulder a disproportionate share of the burden of climate change because of their increased exposure and vulnerability to health threats. Over 90 percent of malaria and diarrhea deaths are borne by children aged 5 years or younger, mostly in developing countries. Other severely affected population groups include women, the elderly and people living in small island developing states and other coastal regions, mega-cities or mountainous areas.
Climate change can lead to dramatic increases in prevalence of a variety of infectious diseases. Beginning in the mid-70s, there has been an “emergence, resurgence and redistribution of infectious diseases”. Reasons for this are likely multicausal, dependent on a variety of social, environmental and climatic factors, however, many argue that the “volatility of infectious disease may be one of the earliest biological expressions of climate instability”. Though many infectious diseases are affected by changes in climate, vector-borne diseases, such as malaria, dengue fever and leishmaniasis, present the strongest causal relationship. Malaria in particular, which kills approximately 300,000 children annually, poses the most imminent threat.
Malaria is especially susceptible to changes in the environment as both the pathogen (Plasmodium) and its vector (mosquitoes) lack the mechanisms necessary to regulate internal temperature and fluid levels. This implies that there is a limited range of climatic conditions within which the pathogen and vector can survive, reproduce and infect hosts. Vector-borne diseases, such as malaria, have distinctive characteristics that determine pathogenicity. These include: the survival and reproduction rate of the vector, the level of vector activity (i.e. the biting or feeding rate), and the development and reproduction rate of the pathogen within the vector or host. These depend on climatic conditions such as temperature, precipitation and humidity.
The ideal temperature range for malaria-carrying mosquitoes is 15–30 °C. Temperature exerts varied effects on survival and reproduction rate of mosquitoes. If initial temperature is high, then an increase in average temperature, associated with global warming, can decrease the survival and reproduction rate of mosquitoes.
Precipitation and humidity 
Mosquitoes are also highly sensitive to changes in precipitation and humidity. Increased precipitation can increase mosquito population indirectly by expanding larval habitat and food supply. Mosquitoes are, however, highly dependent on humidity, surviving only within a limited humidity range of 55-80%.
Extreme weather events 
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. For example, malaria outbreaks have been strongly associated with the El Nino cycles of a number of countries (India and Venezuela, for example). El Nino can lead to drastic, though temporary, changes in the environment such as temperature fluctuations and flash floods. In addition, with global warming, there has been a marked trend towards more variable and anomalous weather. This has led to an increase in the number and severity of extreme weather events. This trend towards 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 towards higher average temperature.
Non-climatic determinants 
As one would expect, climate is not the only determining factor in the spread of malaria. A variety of sociodemographic and environmental influences determine the characteristics of the disease as well. Sociodemographic factors include, but are not limited to: patterns of human migration and travel, effectiveness of public health and medical infrastructure in controlling and treating the disease, the extent of anti-malarial drug resistance and the underlying health status of the population at hand. Environmental factors include: changes in land-use (e.g. deforestation), expansion of agricultural and water development projects (which tend to increase mosquito breeding habitat), and the overall trend towards urbanization (i.e. increased concentration of human hosts). Patz & Olson argue that these changes in landscape can alter local weather more than long term climate change. For example, the deforestation and cultivation of natural swamps in the African highlands has created conditions favourable for the survival of mosquito larvae, and has, in part, led to the increasing incidence of malaria. The effects of these non-climatic factors complicate things and make a direct causal relationship between climate change and malaria difficult to confirm. It is highly unlikely that climate exerts an isolated effect.
Future modelling 
Modelling involves a prediction of the scope, geographic distribution and characteristics of a given factor (malaria in this case) over a period of time. These models are crucial in preparing an adequate public health response to future infectious disease outbreaks. Modelling malaria is particularly complex given the two common pathogen variants (Plasmodium falciparum and Plasmodium vivax) and many regionally dominant mosquito species. These models must therefore incorporate a variety of factors including: human-induced changes in climate (e.g. temperature, precipitation, and humidity), environmental factors (e.g. drought and deforestation), disease factors (e.g. parasite development rate, vector population, and drug resistance) and other factors (e.g. changes in immune status of hosts and spread of disease into new areas). Various models suggest, conservatively, that people living in developing countries’ risk of malaria will increase 5-15% by 2100 due to climate change. In Africa alone, according to the MARA Project (Mapping Malaria Risk in Africa)., there is a projected increase of 16-28% in person-month exposures to malaria by 2100.
Public health response 
Currently, there is no evidence to suggest that the rapid onset of climate change is subsiding. Even if we miraculously managed to stop all greenhouse gas emissions, we would still be faced with the potentially irreversible changes we have already brought. Thus, it is essential that we adapt to these changing conditions. Our response will be both reactive and anticipatory and will need to take place at many levels (legislative, engineering and personal-behaviour). In response to malaria we will need to, for example, improve the quality and accessibility of health services, identify and target response towards vulnerable populations, improve our modelling and surveillance capacity, and implement broad-based public education campaigns.
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As the climate warms, it changes the nature of global rainfall, evaporation, snow, stream flow and other factors that affect water supply and quality. Freshwater resources are highly sensitive to variations in weather and climate. Climate change is projected to affect water availability. In areas where the amount of water in rivers and streams depends on snow melting, warmer temperatures increase the fraction of precipitation falling as rain rather than as snow, causing the annual spring peak in water runoff to occur earlier in the year. This can lead to an increased likelihood of winter flooding and reduced late summer river flows. Rising sea levels cause saltwater to enter into fresh underground water and freshwater streams. This reduces the amount of freshwater available for drinking and farming. Warmer water temperatures also affect water quality and accelerate water pollution.
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Climate change causes displacement of people in several ways, the most obvious—and dramatic—being through the increased number and severity of weather-related disasters which destroy homes and habitats causing people to seek shelter or livelihoods elsewhere. Slow onset phenomena, including effects of climate change such as desertification and rising sea levels gradually erode livelihoods and force communities to abandon traditional homelands for more accommodating environments. This is currently happening in areas of Africa’s Sahel, the semi-arid belt that spans the continent just below its northern deserts. Deteriorating environments triggered by climate change can also lead to increased conflict over resources which in turn can displace people.
Extreme environmental events are increasingly recognized as a key driver of migration across the world. According to the Internal Displacement Monitoring Centre, more than 42 million people were displaced in Asia and the Pacific during 2010 and 2011, more than twice the population of Sri Lanka. This figure includes those displaced by storms, floods, and heat and cold waves. Still others were displaced drought and sea-level rise. Most of those compelled to leave their homes eventually returned when conditions improved, but an undetermined number became migrants, usually within their country, but also across national borders.
Asia and the Pacific is the global area most prone to natural disasters, both in terms of the absolute number of disasters and of populations affected. It is highly exposed to climate impacts, and is home to highly vulnerable population groups, who are disproportionately poor and marginalized. A recent Asian Development Bank report highlights “environmental hot spots” that are particular risk of flooding, cyclones, typhoons, and water stress.
To reduce migration compelled by worsening environmental conditions, and to strengthen resilience of at-risk communities, governments should adopt polices and commit financing to social protection, livelihoods development, basic urban infrastructure development, and disaster risk management. Though every effort should be made to ensure that people can stay where they live, it is also important to recognize that migration can also be a way for people to cope with environmental changes. If properly managed, and efforts made to protect the rights of migrants, migration can provide substantial benefits to both origin and destination areas, as well as to the migrants themselves. However, migrants – particularly low-skilled ones – are among the most vulnerable people in society and are often denied basic protections and access to services.
The links between the gradual environmental degradation of climate change and displacement are complex: as the decision to migrate is taken at the household level, it is difficult to measure the respective influence of climate change in these decisions with regard to other influencing factors, such as poverty, population growth or employment options. This situates the debate on environmental migration in a highly contested field: the use of the term 'environmental refugee', although commonly used in some contexts, is disrecommended by agencies such as the UNHCR who argue that the term 'refugee' has a strict legal definition which does not apply to environmental migrants. Neither the UN Framework Convention on Climate Change nor its Kyoto Protocol, an international agreement on climate change, includes any provisions concerning specific assistance or protection for those who will be directly affected by climate change.
In small islands and megadeltas, inundation as a result of sea level rise is expected to threaten vital infrastructure and human settlements. This could lead to issues of statelessness for populations in countries such as the Maldives and Tuvalu and homelessness in countries with low lying areas such as Bangladesh.
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Conflicts are typically extremely complex with multiple inter-dependent causalities, often referred to as ‘complex emergencies.’ Climate change has the potential to exacerbate existing tensions or create new ones — serving as a threat multiplier. It can be a catalyst for violent conflict and a threat to international security.
The United Nations Security Council held its first-ever debate on the impact of climate change in 2007. The links between climate change and security have been the subject of numerous high-profile reports since 2007 by leading security figures in the United States, United Kingdom and the European Union. The G77 group of developing nations also considers climate change to be a major security threat which is expected to hit developing nations particularly hard. The links between the human impact of climate change and the threat of violence and armed conflict are particularly important because multiple destabilizing conditions are affected simultaneously.
Social impacts 
The consequences of climate change and poverty are not distributed uniformly within communities. Individual and social factors such as gender, age, education, ethnicity, geography and language lead to differential vulnerability and capacity to adapt to the effects of climate change. Climate change effects such as hunger, poverty and diseases like diarrhea and malaria, disproportionately impact children, i.e. about 90 percent of malaria and diarrhea deaths are among young children.
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 U.S. hurricane damage from 1900 to 2005 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.
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 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 defences, could also result in considerable cost-savings in the longterm.
See also 
- A.J. McMichael (2003). "Global Climate Change and Health: An Old Story Writ Large". In A. McMichael. World Health Organization (Geneva). Unknown parameter
- Sahney, S., Benton, M.J. and Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land" (PDF). Biology Letters 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC 2936204. PMID 20106856.
- A.J. McMichael; R. Woodruff, S. Hales (2006). "Climate Change and Human Health: Present and Future Risks". Lancet 367: 859–69. doi:10.1016/S0140-6736(06)68079-3. PMID 16530580.
- Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1.
- http://www.wmo.int/pages/publications/bulletin_en/documents/57_4_short_en.pdf WMO
- P. Epstein (2002). "Climate Change and Infectious Disease: Stormy Weather Ahead?". Epidemiology 13 (4): 373–375.
- J. Patz; S. Olson (2006). "Malaria Risk and Temperature: Influences from Global Climate Change and Local Land Use Practices". Proceedings of the National Academy of Sciences 103 (15): 5635–5636. doi:10.1073/pnas.0601493103. PMC 1458623. PMID 16595623.
- J. Patz; A.K. Githeko, J.P. McCarty, S. Hussein, U. Confalonieri, N. de Wet (2003). "Climate Change and Infectious Diseases". In A. McMichael. Climate Change and Human Health: Risks and Responses (Geneva: World Health Organization). Unknown parameter
- S. Bhattacharya; C. Sharma, R. Dhiman, A. Mitra (2006). "Climate Change and Malaria in India". Current Science 90 (3): 369–375.
- "Nigeria: Duration of the Malaria Transmission Season". mara.org.za. MARA/ARMA (Mapping Malaria Risk in Africa / Atlas du Risque de la Malaria en Afrique). July 2001. Retrieved 2007-01-24.
- J. Patz; D. Campbell-Lendrum, T. Holloway, J. Foley (2005). "Impact of Regional Climate Change on Human Health". Nature (journal) 438 (7066): 310–317. doi:10.1038/nature04188.
- Bogumil Terminski, Environmentally-Induced Displacement. Theoretical Frameworks and Current Challenges, CEDEM, Université de Liège, 2012
- Addressing Climate Change in Asia and the Pacific, 2012
- Bogumil Terminski, Environmentally-Induced Displacement. Theoretical Frameworks and Current Challenges, CEDEM, University of Liège, 2012
- IPCC AR4 SYR 2007. "3.3.3 Especially affected systems, sectors and regions". Synthesis report.
- Mimura, N., et al. (2007). "Executive summary". In Parry, M.L., et al. (eds.). Chapter 16: Small Islands. Climate change 2007: impacts, adaptation and vulnerability: contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press (CUP): Cambridge, UK: Print version: CUP. This version: IPCC website. ISBN 0521880106. Retrieved 15 September 2011.
- "Climate change and the risk of statelessness" (PDF). May 2011. Retrieved 13 April 2012.
- "Summary Statement on Tropical Cyclones and Climate Change" (PDF) (Press release). World Meteorological Organization. 2006-12-04.
- Pielke, Roger A., Jr.; et al. (2008). "Normalized Hurricane Damage in the United States: 1900–2005" (PDF). Natural Hazards Review 9 (1): 29–42. doi:10.1061/(ASCE)1527-6988(2008)9:1(29).
- Insurance Journal: Sound Risk Management, Strong Investment Results Prove Positive for P/C Industry, April 18, 2006.
- "Financial risks of climate change" (PDF). Association of British Insurers. June 2005.
Further reading 
- Addressing Climate Change in Asia & the Pacific 2012
- Climate Change 2007: Synthesis Report, 4th Assessment Report, Intergovernmental Panel on Climate Change
- Report on the Economics of Climate Change (2006), Stern Review
- Human Impact Report: The Anatomy of a Silent Crisis (2009), Global Humanitarian Forum
- Key Points on Climate Justice: Working Paper of the Global Humanitarian Forum
- "What Happened to the Seasons?". Oxfam Research Report.
- Human Development Report 2007/2008, United Nations Development Programme
- Maplecroft Climate Change Risk Report 2009/2010
- Woodward, A. (1995). "Doctoring the planet: health effects of global change*". Australian and New Zealand Journal of Medicine 25 (1): 46–53. doi:10.1111/j.1445-5994.1995.tb00579.x. ISSN 00048291.
- UNESCO (2011) 'Migration and Climate Change'
- Piguet, E., Pécoud, A. and de Guchteneire, P. (2010) Migration and Climate Change: an Overview
- Climate change, water stress, conflict and migration Proceedings of a conference in The Hague, September 2011
- Global Humanitarian Forum
- Tck Tck Tck Time for Climate Justice campaign
- United Nations Environment Programme and climate change
- Office of the High Commissioner for Human Rights human rights and climate change
- Office of the High Commissioner for Refugees climate change
- Care International Climate Change Information Centre
- Red Cross/Red Crescent Climate Centre
- World Bank and Climate Change
- World Meteorological Organization and climate
- Climate change and human health on World Health Organization
- International Alert climate change and violent conflict
- International Strategy for Disaster Reduction disaster risk reduction and climate change