A Review of Effects of Environmental Change on Human Health

Email: uuupaudel22@gmail.com uttampdl12@gmail.com Abstract: Current knowledge production on the effects of environmental exposures on human health reflects technological, social and economic development broadly; theoretical and methodological advancements in social science and medicine more specifically. Human health and the welfare mainly rely on refurbishing and protecting the integrity of the natural systems such as fresh air, safe water, biodiversity, toxic waste management and proper land reform which upkeep life in the natural environment and abating the human impact that has a negative impact on ecologically sustainable development. A massive number of scientific evidence are available in the enlightenment of environmental health issues, however, scanty literatures are found covering economically valued effects of environmental change on communicable and non-communicable diseases. Ergo, this review paper has reviewed selected papers from 1990 to 2018 and tried to identify the research gaps in effect within some components of environmental health economic issues in South Asia and Nepal. More importantly, nationally representative economic evaluation of environmental effects (air pollution, water resource management, toxic pollutants and biodiversity loss) on human infectious and non-infectious diseases are the lack for the policymakers and economic evaluation of effects of climate change on health is the unreached area of researchers in Nepal. Moreover, none of the Nepal based scientific papers are found published regarding the association of climate change with malnutrition, rate of chemical exposure to dare human health and human stress including psychosocial factors Obtaining these unreached literatures are worthy of climate policy development and implementation in developing countries associating with universal health coverage.


Introduction
Environmental change embraces the change in the framework of natural human surroundings, which include biophysical components and processes of natural environment of land, water and air including all layers in the atmosphere, inorganic and organic matters (both living and non-living), socio-economic components and processes of the human environment mainly associated with the human health hazards. Environmental sustainability, economic efficiency and social equity provide a balancing act and sometimes compromising level of sustainable development (Oiamo, 2014).
Through the economic perspective towards environmental change, a detrimental change in environmental components i.e., environmental degradation create multiplier negative effects in the various sectors of economy of a nation, especially on health and agricultural sectors of developing economies. A study (Podesta and Ogden, 2008) suggests that while long-term environmental events, such as droughts, have no significant effect on internal migration, but sudden-onset environmental events in the form of floods significantly increase the likelihood of migration, a big international socio-economic issue. For example, approximately 600,000 people in Bangladesh and 4 million in the Philippines have been migrated because of storms, floods, droughts and landslides since the 1970s.
Environment-poverty trap can easily arise for a poor rural household with access to only marginal lands and natural resources for its own production, lack of nutritional status and the capacity for work by the poor (Barbier, 2010). On the other side, a study shows that social vulnerability increases with increase in environmental degradation (Luers, 2005). Poverty reduction will not necessarily lead to an improved environment unless specific environmental action is taken. A study in Pakistan argues that trade liberalization promotes environmental degradation by the export of environmental capitals (Khan et al., 2001).
Public investment in environmental infrastructure should target poor households because investment in clean water and sanitation creates positive externalities for household health outcomes strongly linked to the environment in poor countries.
Environmental degradation and social injustice exert worldwide the greatest effects on the health of individuals and populations (Donohoe, 2003). Human depression caused by high salinity, asthma, suicide and heart disease with salinity can be expected to increase in rural areas in the future, further adding to the burden of disease associated with environmental degradation (Speldewinde et al., 2009;Fearnley et al., 2014). Increasing efficiency, reducing waste and properly valuing resources, will help reshape the structure of growth and reduce undesirable environmental impacts (Munasinghe, 1999).
An estimated 12.6 million deaths each year are attributable to unhealthy environments -nearly one in four of total global deaths. A bulletin of World Health Organization (WHO) has explored environmental risk factors, such as air, water and soil pollution, chemical exposures, climate change and ultraviolet radiation, contribute to more than 100 diseases and injuries (Ref. http://www.who.int/phe/en). An econometric analysis has proved that income inequality and environmental degradation have a negative and significant impact on life expectancy in Pakistan, with unidirectional causality running from environmental degradation to life expectancy (Ali and Audi, 2016).
Environmental threats to the health of children in Southeast Asia and the Western Pacific are myriad and include the classic infectious disease hazards: Pneumonia, dengue, malaria, dysentery, measles, AIDS and tuberculosis (WHO, 2017a;Zuckerman, 2012;Bonjour et al., 2013). The major environmental problems of South Asia including Nepal are degradation of air quality, drinking water, natural resources, lack of solid waste management, surface water quality, water resources, a release of toxic pollutants, loss of biodiversity, impacts of climate change and improper land use (CES, 2015).
The focus of this paper is to identify the evidence gap of environmental factors that are relatively testimony in attributing internationally to dare the human health and other economic sectors of WHO South East Asian region and others. Some potential research and review papers are selectively chosen by developing criteria for each component to ensure the idea to go in depth for a factor of environmental changes and its effects on human health. First, the papers were collected from Google Scholar, Science Direct, PubMed and Environmental health Journals. During the selection of papers to be reviewed, criteria that the paper should directly or indirectly include all three components: environment, health and economic or econometric issues, desirably health cost; is set for the sake of finding evidence gap in Nepal and reviewed all the valued papers from 1990 to 2018 chronologically. The major components of environmental change that affect human health are reviewed based on some selected potential past pieces of evidence.

Air Pollution and Health
Studies at the beginning of the 1990s commonly argue that bad air pollution in cities of developing and developed countries are chronic coughing and susceptibility to infections, while deaths from air pollution occur primarily among the elderly, the infirm and the very young (Sattenspiel, 2000;Patz et al., 1996). Bronchial inflammations, allergic reactions and irritation of the mucous membranes of the eyes and nose all indicate that air pollution must be reduced (Mabahwi et al., 2015). Until 2005, WHO estimated that 2 million children under age 5 die each year from acute respiratory diseases exacerbated by air pollution (Mabahwi et al., 2015). People suffering from respiratory diseases are the most likely to be affected by air pollutions. In addition, not just air pollution can cause health effects, the study also shows that air pollution can cause stress to a human being (Mabahwi et al., 2014). WHO has economically estimated that the total health damage from air pollution (particulate matter) in China amount to 2.4-4.9% of the city's GDP; while in India, the total costs of health impacts were estimated at US$ 113 million for a 50-mg/m 3 increase in PM 10 and US$ 218 million for a similar increase in NO 2 (WHO, 2016a).
As listed by the American Lung Association-2013, people that are at risk of particulate matter are infants, children and teens, people over 65 years old, people with lung disease (asthma, chronic pulmonary disease, chronic bronchitis and emphysema), people with heart disease or diabetes and people who work and active outdoors. Air pollution not just will harm human health but also other aspects of the environment such as visual qualities, vegetation, animals, soils and water quality (Mabahwi et al., 2014). The recent studies seem much specific towards early warning air quality daring human health (Mabahwi et al., 2015;Tin et al., 2016). Interestingly, few recent papers including review paper concluded that psychosocial factors are mainly responsible to inform public health communications used during air pollution episodes (Mabahwi et al., 2014;Tin et al., 2016;D'Antoni et al., 2017;Fuller et al., 2017;Pruss-Ustun et al., 2016;Singh et al., 2017). Regarding health cost, the indoor air pollution from traditional cooking energy increases chronic bronchitis, asthma and acute respiratory infections, accordingly, health cost due to dirty cooking fuel is US$ 16.94 per rural household (Pant, 2012) and health benefit from the reduction of dirty fuel is many times higher than the cost (Pant, 2008).

Drinking Water and Health
About 2 million deaths and 15% of total child mortality in the world can be avoided by providing universal access to safe water and sanitation services, moreover, safe drinking water significantly reduces diarrheal diseases and other illnesses such as intestinal Helminth infections, Schistosomiasis and trachoma (Murty and Kumar, 2002;Prüss-Üstün et al., 2008;Gorchev and Ozolins, 2011;WHO, 2014). The burden of malaria with water management could be reduced by environmental modification and modification of human habitation by 88% (Prüss-Üstün et al., 2008), this result shows that malaria control program that emphasizes environmental management is highly effective in reducing morbidity and mortality and can lead to sustainable malaria control approaches.
The economic benefit from the drinking water resources management is estimated at $84 billion including health care saving, averted mortality and mortality, productivity gains, time cost and others (Prüss-Üstün et al., 2008). After the publishing of WHO guidelines for safe drinking water, a study covering all WHO member countries, following a multilevel modeling approach, concluded that if the trend remains same, improved water access will not be only for 10% of the world population, making significant prevention on health hazards . If water quality can be ensured up to the point-of-consumption, diarrhea can be reduced significantly by between 28 and 45%, depending on the type of water supply, basically pipe water supply. Especially, in South Asia, there is a significant reduction in the occurrence of the disease through pipe supply (WHO, 2014).
A study using standardized cross-culturally valid household water insecurity scale among pregnant and HIV infected women of Kenya concluded that household water insecurity causes psychosocial impacts, economic impacts and main transmission of diseases (Krumdieck et al., 2016). Global Analysis and Assessment of Sanitation and Drinking-Water presents that though countries are showing a high level of responsiveness to the SDGs, with a majority of countries in the process of setting or planning to set targets that take into account the SDGs in the next few years; the estimated capital investment needs to reach the SDGs that are three times higher than current investment levels, significantly more resources will be required to address the financial gap and overall improving health and well-being.
For this, a country-level study addressing the possible domestic resources in the management of drinking water, a proxy of better human health from preventing water-borne diseases, seems urgent. A recent review paper with coverage since 2011 to 2015 explored that 381 new outbreak of water-borne diseases are the major cause of water knowledge and environmental degradation (Efstratiou et al., 2017). But such recent potential evidence is not found for least developed countries like Nepal.

Surface Water and Health
An old but potential study measuring economic benefit of surface water quality improvement in relation to environmental issue analysis through non-market valuation method explains that water pollution problem is not in priority of the household problem rather they are highly conscious on environmental concerns, such as deforestation and poor solid waste collection and disposal (Choe et al., 1996). Globally, 50% of drinking water needs are fulfilled by surface water which is the main cause of transmitting diseases for far distance and 91% of the global population has an excess of improved drinking water but 159 million of these people rely on untreated surface water, which poses even greater health risks than other water sources (WHO, 2016b). As population pressures increase, the issues of water quality will become a global issue. The water cycle including wastewater and surface water needs to be managed in a holistic way to protect limited freshwater resources, for the protection of human health from waterborne infectious diseases and toxic chemicals (WHO, 2016b). But the recent studies are devoted only to ingredients presents in the surface water rather than most importantly devoting towards the source of surface water pollution leading health hazards.

Solid Waste Management and Health
A global estimation of urban solid waste presents that 4.3 billion urban residents will generate about 1.42 kg/capita/day of municipal solid waste by 2025.that may have huge economic cost (Manaf et al., 2009). In developing countries, solid wastes from the hospital and chemical industries are more hazardous through the perspective of health than the general waste from households and density of waste produced in these countries is also high relative to the developed countries (Zurbrugg and Eawag, 2013). Economically sound countries are also now in the process of establishing a holistic, integrated and cost-effective solid waste management system (Manaf et al., 2009). A study undertaken in India found that excreta and other liquid and solid waste from households and the community, are a serious health hazard and lead to the spread of infectious diseases (Alam and Ahmade, 2013). Poor handling and disposal of waste are the major causes of the environmental pollution, leading to the breeding place for the pathogenic organism and spread of infectious diseases (Boadi and Kuitunen, 2005). More than 70% of the solid wastes generated in Nepal are of organic origin (Pokhrel and Viraraghavan, 2005), for which recently recycling coupled with composting is conceptualized to reduce the environmental impact and economic benefits in South Asian countries (Ikhlayel, 2018). Beyond this, no more papers are found addressing solid waste management and health cost burden in South Asia including Nepal.

Toxic Pollutants and Health
Health problems attributed to the presence of toxins from cyanobacteria in drinking water have been reported in a number of countries, including Australia, Brazil, China, England, South Africa and the USA (Terzopoulou and Voutsa, 2017), but later evidence claims that anthropogenic activities contribute to the spread of toxic chemicals, especially Cd, Hg, Pb and As, into the environment, including several toxic metals and metalloids, increasing the levels of human exposure to many of them, representing a serious threat to human health. There have been identified 37 toxic organic pollutants in the crude sewage from the investigation of Chinese research which has severe and long-term impacts on environment and ecology (Jang et al., 2003;Liu et al., 2017). The study conducted in China concluded that adsorption treatment and the physicochemical-biochemical combined process seems suitable for high concentration semi coking wastewater treatment (Liu et al., 2017).
A technical study found that persistent toxic pollutants representing three classes: organo-chlorinated pesticides, polychlorinated biphenyls and polycyclic aromatic hydrocarbons are the major pollutants in water, moreover micro-pollutants such as benzanthracene, benzofluoranthene, dichlorodiphenyl dichloroethane, endosulfan II, methoxychlor and pyrene should not be neglected (Terzopoulou and Voutsa, 2017). However, any recent such technical study is not found in the context of developing countries. An economic evaluation of WHO estimated that annual illness costs of acute poisonings in Nepalese farmers due to pesticide use was nearly onethird of total annual health-care costs (WHO, 2016a). Though many pieces of evidence are available regarding health consequences, economic analysis of health consequences because of toxic organic pollutants contaminating environment are very limited and totally lack developing countries.

Loss of Biodiversity and Health
Environmental change has negatively affected most biological systems on our planet and is becoming of increasing concern for the well-being and survival of many species (Tjaden et al., 2017;MOHP, 2011). Biodiversity conservation including green space, vegetated areas, flora and fauna; creates health benefits including obesity reduction, lowered blood pressure, extended lifespan, positive impacts on mental health particularly through stress reduction and attention restoration, faster surgical recovery, patient healing and higher pain thresholds, child development through play and motor skill development, improved concentration, well-being and increased physical activity, purify the air by filtering atmospheric pollutants include nitrogen dioxide and sulphur dioxide and larger particulate matter (Davern et al., 2017).
Through the perspective of infectious diseases, there is debate among the literature regarding a negative or positive association between burdens of infectious diseases and biodiversity, rather biodiversity is different for different countries. However, a recent study with the aim to investigate the spatial and temporal relationships between Disability Adjustment Life Years (DALYs) lost to infectious disease and potential demographic, economic, environmental and biotic drivers found that countries with high biodiversity have high disease burdens, consistent with the expectation that high diversity of potential hosts should support high disease transmission (Young et al., 2017).
Moreover, urbanization and wealth were associated with lower burdens for many diseases, a pattern that could arise from increased access to sanitation and healthcare in cities and increased investment in healthcare. The importance of urbanization and wealth helps to explain why most infectious diseases have become less burdensome over the past three decades and points to possible levers for further progress in improving global public health (Ostfeld, 2017;Murray et al., 2012).

Weather Events and Human Health
Extreme weather-related mortality in the United States shows that two third of total deaths are due to excessive natural heat and remaining are due to excessive cold and others (Jiang et al., 2015). Recently it has been predicted that extreme hot weather events may cover 72% of the national population of Korea by 2090s if current trend remains same (Shim et al., 2017). Unexpected excess rainfall in Europe has made water contaminated with Arsenic and Antimony, subsequently degrading to the human health through the food chain (Cann et al., 2013). A modeling aspect of extreme weather events and human vulnerability in Europe predicts that Europe will have two third population vulnerable in terms of a climatic effect on human health by the end of this century (Forzieri et al., 2017). Similarly, heat-related weather events claimed 2248 deaths in 2015 in India (Hashim and Hashim, 2016) meaning that extreme weather events under climate change are directly or indirectly increasing the disease occurrence in South Asian countries including Nepal.

Climate Change and Health
Global warming and instability of the climate play increasingly important role in stimulating the global emergence, resurgence and transmission of infectious diseases, reported 30 new diseases and resurgence of many old diseases all over the world since 1975 (McMichael et al., 1996). Regarding evidence on climate-induced infectious diseases, biological and mathematical previous model to analyze the relationship between climatic change and intensity of change in infectious diseases are particularly lacking with the inclusion of non-climatic factors to dare the disease pattern change (McMichael et al., 2006). The South East Asian meet 2008 in India declared that the adaptation to inevitable effect of climate change is urgent to prevent a gigantic cost in terms of infectious diseases, health-care expenditure and lost productivity (WHO, 2009a). Scanty literatures evaluating economic impacts of climateinduced change in human health, viz. cardiovascular and respiratory disorders, diarrhea, malaria, dengue fever and schistosomiasis; have the problems with calculating Gross Domestic Product (GDP), welfare and investment fall (rise) in regions with net negative (positive) health impacts emerged by climate change and direct cost estimates; common in climate change impact studies; and underestimating the true welfare losses (Bosello et al., 2006). United States Climate Change Program presented that the impacts of climatic upsets in urban areas are likely associated increases in tropospheric ozone concentrations can contribute to or exacerbate cardiovascular and pulmonary illness and will likely be an increase in the spread of several food and water and vector-borne pathogens among susceptible populations depending on the pathogens' survival, persistence, habitat range and transmission under changing climate and environmental conditions (Forman et al., 2008). Also, the challenge posed by climate change on some new emerging diseases such as HN influenzas and SARs in some specific region can be reduced through strengthening local public health and medical capacity in a sustainable way (Ali et al., 2016).
Children's mental and physical health is adversely affected by forced migration and population displacement, perpetuating poverty and civil unrest in low-income and developing countries (Sheffield and Landrigan, 2011). Countries in the WHO South-East Asia Region are particularly vulnerable to a changing climate. Most recently, changes in extreme weather events, undernutrition and the spread of infectious diseases are projected to increase the number of deaths due to climate change by 2030, indicating the need to strengthen activities for adaptation and mitigation (TWB, 2010;Forzieri et al., 2017).
National action plans for climate change generally identify health as one of their priorities; however, limited information is available on implementation processes and to increase the capacity of health systems to manage the health risks of climate change in South-East Asia, if population health is to be protected and strengthened while addressing changing weather and climate patterns. Enhancing the resilience of health systems is key to ensuring a sustainable path to improved planetary and population health (Bowen and Ebi, 2017). Therefore, climate change is the major environmental factor in the emergence of new diseases, an outbreak of diseases and overall health cost burden responsible for the human being.
The major challenges for Sustainable Development Goals (SDGs) health-related indicators including 2030 agenda remain in terms of reducing maternal and child mortality, improving nutrition and achieving further progress in the battle against infectious diseases such as HIV/AIDS, tuberculosis, malaria, neglected tropical diseases, hepatitis etc. Evidence from economics based data on climate change, water and sanitation and air quality seem urgent needs to be done to reduce risks to health to recover the present major deficiencies in universal health coverage for basic health services and inadequate preparedness for health emergencies (WHO, 2017b;2016c). The increased frequency and intensity of extreme climatic events can cause not only injury, but also increase the risk of water-borne diseases such as diarrheal disease, Hepatitis A and E; bacterial diseases such as cholera; diseases associated with crowding (measles, meningitis, acute respiratory infections) and vector-borne diseases such as malaria, dengue as well as psychological and emotional distress related to traumatic events in WHO Southeast Asian region (WHO, 2017a;ASCI, 2009;ADB, 2008).
WHO-South East Asian environmental report has a primary focus on only environmental issues including climate change and air pollution of the countries Maldives, India and Nepal. The Maldives is comparatively less vulnerable to air pollution and solid waste management but highly affected by limited freshwater resources, heat-related illnesses, limited infectious diseases etc which are climate sensitive issues. Indian case is too vulnerable regarding air pollution, climate change, water pollution and other environmental degradation. Besides air pollution in Nepal and Bangladesh, climate change is the top challenge on health sectors where mitigation and adaptation strategy with a common program, National Adaptation Program of Action, has made ready to implement as a national plan and strategy for addressing the health risks of climate change (WHO;2017a;2017b;ASCI, 2009;ADB, 2008;Unit et al., 2001).
Climate change and health outcomes in South Asia is an issue that demands collaboration to develop the synergies needed to produce powerful responses (Bowen and Ebi, 2017). On the other side, Nepalese people need in improving preparedness and adaptation strategies such as coping effectively with diseases through improvement of infrastructure and facilities, assessing and educating the vulnerable section of society and enforcing regulations to protect the environment . This study mainly focuses on the review of the direct and indirect association climate change (a proxy for an environmental change) and human diseases. Therefore, this paper has thoroughly reviewed the most relevant papers summarised in Table 1   (General Circulation Model-GCM) increased in higher altitude and less economically developed areas due to temperature and rainfall change. Jetten et al. (1996), Simulation Models Dynamic vectorial capacity model for malaria prediction which Netherlands predicts that malaria cases significantly increases with a 2-4°C temperature increase. Colwell (1996), Bangladesh Logit model The positive association between Sea surface temperature and cholera outbreak.

Martens (1998), Netherlands
Eco-epidemiologic Increase in temperature increases the vector-borne diseases modeling approach (VBD) and deteriorates agriculture, vegetation and migration. Patz et al. (1998), USA General circulation model 1.16°C temperature increase by 2050 in temperate regions will have 47% higher risk of dengue. Sutherst (1998), Australia CLIMEX approach, a spatial CLIMAX is the best tool for the analysis of VBD integrated assessment model, and climate risks. Githeko et al. (2000), WHO Descriptive regional Analysis El'Nino temperature up by 1-3.5 0 C by 2100 will encourage the outbreaks of vector-borne diseases in all regions increasing the cost of treatment.

McMichael and Kovats
Descriptive Study Biological, behavioral and social modes of adaptation strategy (2000)  Multi-level linear regression A one-degree Celsius increase in maximum monthly average models, age-adjusted mean temperature is associated with a 0.34 increase in Heat-stress Illness in highly urbanized counties. Liang and Gong (2017) Review of evidence Geographically, regions experiencing higher temperature anomalies have been given more research attention; unfortunately, the Earth's most vulnerable regions to climate variability and extreme events have been less studied. Curriero et al. (2001), USA Monte Carlo version of the Fifty-one percent of waterborne disease outbreaks associated Fisher exact test was with precipitation events above the 90th percentile and 68% by events above the 80th percentile. Ordinary-differential-equation model A potential model derivation to quantify the seasonality of the South Africa population, vector population dynamics and to predict An. arabiensis population dynamics. Kulinkina et al. (2016), Time series analysis Higher ambient temperature decreased and higher rainfall India increased diarrheal risk with the temperature being the predominant factor in urban and rainfall in rural sites Phung et al. (2016), Interrupted time-series Levels of infectious intestinal diseases following a heavy Vietnam method, meta-analysis rainfall event increase from 7.3 to 13.5% for lags from 0 to 21 days. Extreme Weather Events and Diseases Occurrence Greenough et al. (2001), USA Descriptive Study Extreme weather events such as precipitation extremes, El'Nino and severe storms caused hundreds of deaths and injuries annually in the United States. Wu et al. (2007), Taiwan Autoregressive integrated Weather variability is a significant indicator of the increasing moving average models occurrence of dengue fever. Gullón et al. (2017), Spain

Rainfall and Infectious Diseases
Mixed-Effects Poisson regression There is an increased risk of Hepatitis A 2 weeks after water-related climate events. Kjellstrom et al. (2017) Descriptive study Occupational health is particularly affected by high heat exposures in workplaces, which will be an increasing problem by the end of this century in South Asian Region (Nepal, Maldives, India and Bangladesh). Climate Change, Vulnerability and Adaptation/Mitigation IPCC (2007a), South Asia Descriptive Study By 2050, freshwater in South Asia is projected to decrease; heavily populated regions will be at greatest risk due to increased flooding leading high economic cost due to diarrheal disease. Gamble et al. (2008), USA Descriptive study Vulnerabilities are shaped not only by existing climatic exposures, sensitivities and adaptive capacities but also by responses to risks. Hijioka et al. (2014), Asia Descriptive Study Increases in heavy rain and temperature will increase the risk of diarrheal diseases, dengue fever and malaria in South Asia. Oppenheimer et al. (2015) Descriptive Study Vulnerability and key climate change risks in light of criteria are found as risk of death, injury, ill-health, coastal flooding and sea level rise.   Bhandari et al. (2012), Nepal Time series analysis There is statistically significant correlation between diarrheal cases occurrence and temperature and rainfall. Dhimal et al. (2014), Nepal Cross-sectional Study, 1°C increase in minimum and mean temperatures increase Hotpot analysis malaria incidence by 27 and 25% respectively. Dhimal et al. (2015), Nepal Cross-sectional study Climatic variables; rainfall, temperature and relative humidity seem significant predictors of chikungunya and dengue virus vectors abundance. Dhital et al. (2016), Nepal Review study Direct and indirect climatic effect on health could be expected further enhanced with social and environmental differences within the country. Pant et al. (2017), Nepal Descriptive and spatial analysis There is a strong clustering of Japanese Encephalitis incidence in monsoon season in the south-western and south-eastern Terai region of Nepal Cost Burdens of Climate-sensitive Diseases and Outcomes Tol (2002) GCM based Model, Globally, a 1°C warming would be a positive 2% of gross world Meta-analytical methods product, with a standard deviation of 1% including health cost. IPCC (2007b) Top-down modeling Global modeled climate costs are sensitive with some regions, sectors (e.g., land-use), use of revenues from carbon taxes and auctioned permits, co-benefits of mitigation measures, or equity issues. Ebi (2008) Predictive cost estimation At 750 ppm CO2 emission, the costs of treating diarrheal diseases, malnutrition and malaria in 2030 is estimated to be $4 to 12 billion worldwide. UNFCCC, 2009 Review study Costs of adaptation through an aggregate level analysis and disaggregated approach provides better estimates at the sectoral level, but faces considerable uncertainty. WHO (2009b) Descriptive analysis A need for cost-effectiveness of interventions to protect health from climate change and monetized health benefits is higher than mitigation costs. Hutton (2011) Review study Global adaptation cost studies carried out so far indicate health sector costs of roughly US$ 2-5 billion annually. Yoon et al. (2014) Disability-adjusted life Cerebrovascular diseases caused by heat waves accounted for years (DALY) 72.1% of the total burden of disease (in DALYs) in South Korea. McDonald et al. (2015) Climate health justice model Asthma, ischemic heart disease, diarrhea and heat exhaustion/cramps/stroke/syncope charges amounted to US$5.6 billion in 2008 to 2010. Hsiang et al. (2017), USA Spatial empirical adaptive The total value of market and nonmarket damage due to global assessment system mean temperature costs roughly 1.2% of gross domestic product per +1°C on average.
First, the literatures are systematically managed and reviewed chronologically as per the relevancy of the climate disease relationship, then the literatures specific to certain climatic components and their effects on health are reviewed, and finally the papers based on climatic vulnerability, adaptation and the cost burden raised by climatic hazards are adequately reviewed covering international to local potential publications and reports. Improved economic assessments associated with the health cost of climate change can be essential in health adaptation programs and support mitigation policies that enhance health. Economic evaluations of mitigation policies could explore the major health co-benefits, covering much of the cost of the initial investment. But special methods particularly on how best to represent uncertainty, the relative value of future benefits (e.g., discounting) and the achievement of equity is quite difficult. If these methods applied to assess the health costs of inaction on climate change, the costs and benefits of investing in health adaptation, at the global, regional or local level, as well as of mitigation actions impacting on health would be more accurate. But the country-based papers till the date are limited to find the partial cost of whole damage made by climatic hazards.

Conclusion and Evidence Gap
Environmental degradation causes multiple negative multiplier effects leading unstable global health situation. As referring to a truncated review of the major environmental factors, in fact, helped to identify the present daring major factor to human health, especially increasing future and present health cost by promoting regular new disease occurrence. From the review of past evidence, an association of air pollution with human stress and economic cost of stress, a recent matter of medical discussion, is one of the potential research gaps in south Asia. None of the paper is found finding a social burden in terms of cost due to water-borne diseases. Similarly, effects of climate change on toxic pollutants which have indirect health consequences is also an unreached area of researchers in the context of Nepal. Solid waste management in the South Asian region are major challenges for the prevalence of new diseases, but the pieces of evidence are devoted only to exploring challenges rather than cost-effective management scenarios. Air pollution could be controlled by the human, but climate change might be inevitable to cause several diseases and other vulnerability or hazards. Therefore, climate change is the major component of the environmental changing factor to be studied economically in relation to the human health where the community is most vulnerable or sensitive to climate change.
Extreme weather events under climate change in terms in temperature, humidity and rainfall has been increasing health vulnerability and claiming the human life and other morbidities in South Asia including Nepal, though there is not found any recent potential research to build research-based effective adaptation and mitigation action plan implementation in Nepal. Almost all the scientific studies from 1990 to 2000 are found based on the descriptive methods in the explanation of climatehealth relationship. Few papers addressed some predictions over the climate risk assessment daring human diseases by 2050. Similarly, the studies from 2001 to 2010 are found quite extended in the response of global to local climate change issues daring human health from several dimensions. And the recent papers from 2011 to the date are devoted to exploring the sensitivity of climatic variability towards communicable and non-communicable diseases.
While reviewing the methodological sections of the entire evidence, a deficiency on the geographical databased study including social, economic, climatic, ecological factors as well as human immunity, undernutrition, physical infectious diseases and mental health is found. More specifically, vector-borne diseases, foodborne diseases and water-borne diseases are most sensitive to heat stress and rainfall in South Asia. Therefore, as other studies, this study also concludes with a need of advanced ecological niche modeling, entomological surveillance, early warning system and country-wise spatial and temporal scales economic evaluation based studies including socioeconomic factors to be adopted in the analysis of future studies.
Regarding temperature-diseases relationship, almost all the papers seemed devoted to finding the present association and future consequences of heat-related temperature change towards the increase and outbreaks of many infectious diseases such as malaria, dengue, cholera and few other diseases related mortality. Similarly, rainfall and precipitation are associated with waterborne diseases and drinking water-related diseases. But few studies have recommended for multivariate analysis including climatic and non-climatic factors may yield the robust result to the policymakers. However, all the papers are with the lack of proper recommendation for future consequences of diseases due to extreme rainfall. It is suggested that eco-climatic condition, geographical condition, water supply, sewage system, solid waste collection and appropriate adaptation strategy are to be addressed. Regarding weather extreme and infectious diseases, El'Nino oscillation is the major for human diseases such as Hepatitis A, malaria, dengue and other infectious and non-infectious diseases are highly sensitive to extreme weather events. Variations of socio-ecological changes, diseases transmission patterns, disaster resilience programs, early warning capabilities, cultural practices etc are the major issues to be taken into account while protecting health from extreme weather events.
South Asia based studies provides the evidence gap that all the south Asian countries should conduct country-wise national analytical and multi-dynamic research including climatic and non-climatic indicators through economic perspective for the generation of selfmotivation in the country to local level, especially aquaculture productivity, reduced physical work, flood, heat waves, draughts, under-nutrition, mental health, infectious disease etc. in the short run and food security, water shortage, flood related injuries, diseases, mental disorders etc. are to be addressed while studying health consequences of climate change in the long run. In Nepal, vector-borne diseases-Chikungunya malaria, dengue, Japanese Encephalitis; water-borne diseasesbacillary diarrheal disease including cholera; foodborne diseases, malnutrition, cardiorespiratory diseases, psychological stress and health effects and injuries related to extreme weather are major climate-sensitive health risks whose prospective longitudinal study with the inclusion of economic evaluation on climatic effect over health seems an urgent need for the development of climate adaptation policy and health system management accordingly in the country.
Climate change influences human health in various ways and quantitative assessments of the effect of climate change on health at the national level are becoming essential for environmental health management. The evidence is seemed devoted to finding the climate caused heath cost partially as the damage costs, but these evaluations of costs cover the fraction of the total societal cost. Economic evaluation of adaptation cost is, therefore, seemed urgent to inform the policymakers in the formulation of better health perspective associated with climatic hazards. Global assessment of the cost of climate change is measured in terms of GDP or welfare or investment. Less than ten scientific pieces of evidence are found in the estimation of health cost of climate change by employing sum methods and spatial empirical adaptive global-to-local assessment system, only being based on the developed country database. Therefore, beyond past myopic evidence, an integrated country-wise south Asian level study using multivariate analysis to find the relationship between environmental change and diseases incidence including socioeconomic and household behavioral factors is seemed urgent to reduce the current climatic vulnerability encouraging unknown outbreaks of emerging and re-emerging diseases; and private public health cost burden.

Funding Information
This review paper has prepared without any external funding source.