effects of climate change on human health effects of climate change on human health the effects of climate change on human health are increasingly well studied and quantified. they fall into three main categories: (i) direct effects (e.g. due to heat waves, extreme weather events), (ii) impacts from climate-related changes in ecological systems and relationships (e.g. crop yields, marine productivity), and (iii) the more indirect consequences such as impoverishment, displacement, and mental health problems. heat stroke treatment at baton rouge during 2016 louisiana floods. climate change is making heat waves more common, potentially leading to a higher risk of heat stroke. more specifically, the relationship between health and heat includes the following main aspects: exposure of vulnerable populations to heatwaves, heat-related mortality, reduced labour capacity for outdoor workers and impacts on mental health. there is a range of climate-sensitive infectious diseases which may increase in some regions, such as mosquito-borne diseases, cholera and some waterborne diseases. health is also acutely impacted by extreme weather events (floods, hurricanes, droughts, wildfires) through injuries, diseases, and air pollution in the case of wildfires. other indirect health impacts from climate change may be rising food insecurity, undernutrition and water insecurity. disadvantaged populations are especially vulnerable to climate change impacts.: 15 for example, young children and older people are the most vulnerable to extreme heat. the health effects of climate change are increasingly a matter of concern for the international public health policy community. already in 2009, a publication in the well-known general medical journal the lancet stated: "climate change is the biggest global health threat of the 21st century". this was re-iterated in 2015 by a statement of the world health organisation. in 2019, the australian medical association formally declared climate change a health emergency. studies have found that communication on climate change is more likely to lead to engagement by the public if it is framed as a health concern, rather than just as an environmental matter. background effects of climate change this section is an excerpt from effects of climate change. climate change affects the physical environment, ecosystems and human societies. changes in the climate system include an overall warming trend, more extreme weather and rising sea levels. these in turn impact nature and wildlife, as well as human settlements and societies. the effects of human-caused climate change are broad and far-reaching, especially if significant climate action is not taken. the projected and observed negative impacts of climate change are sometimes referred to as the climate crisis. the changes in climate are not uniform across the earth. in particular, most land areas have warmed faster than most ocean areas, and the arctic is warming faster than most other regions. among the effects of climate change on oceans are an increase of ocean temperatures, a rise in sea level from ocean warming and ice sheet melting, increased ocean stratification, and changes to ocean currents including a weakening of the atlantic meridional overturning circulation.: 10 carbon dioxide from the atmosphere is acidifiying the ocean. recent warming has strongly affected natural biological systems. it has degraded land by raising temperatures, drying soils and increasing wildfire risk.: 9 species worldwide are migrating poleward to colder areas. on land, many species move to higher ground, whereas marine species seek colder water at greater depths. at 2 °c (3.6 °f) of warming, around 10% of species on land would become critically endangered.: 259 climate change vulnerability a 2021 report published in the lancet found that climate change does not affect people's health in an equal way. the greatest impact tends to fall on the most vulnerable such as the poor, women, children, the elderly, people with pre-existing health concerns, other minorities and outdoor workers.: 13 there are certain predictors for health patterns of people which will determine the social vulnerability of the individuals. these can be grouped into "demographic, socioeconomic, housing, health (such as pre-existing health conditions), neighbourhood, and geographical factors". types of pathways affecting health illustration for the effect of climate change on human healthclimate change is linked with health outcomes via three main pathways:: figure 2 direct mechanisms or risks: changes in extreme weather and resultant increased storms, floods, droughts, heat waves (wildfires also fit here) indirect mechanisms or risks: these are mediated through changes in the biosphere (e.g., in the burden of disease and distribution of disease vectors, or food availability, water quality, air pollution, land use change, ecological change) social dynamics (age and gender, health status, socioeconomic status, social capital, public health infrastructure, mobility and conflict status) these health risks vary across the world. for example, differences in health service provision or economic development will result in different health risks for people in different regions. overview of health impacts general health impacts the direct, indirect and social dynamic effects of climate change on health and wellbeing produce the following health impacts: cardiovascular diseases, respiratory diseases, infectious diseases, undernutrition, mental illness, allergies, injuries and poisoning.: figure 2 health and health care provision can also be impacted by the collapse of health systems due to climate-induced events such as flooding. therefore, building health systems that are climate resilient is a priority.: 15 mental health impacts this section is an excerpt from effects of climate change on mental health. smoke in sydney (australia) from large bushfires (in 2019), affected some people's mental health in a direct way. the likelihood of wildfires is increased by climate change.part of a series onclimate change andsociety effects mitigation adaptation economics business action climate finance economic impacts economics of mitigation emissions trading low-carbon economy social issues agriculture cities climate justice children ethics gender indigenous people fisheries human rights security poverty migration women health and psychology climate grief eco-anxiety infectious diseases mental health psychology of denial waterborne diseases communication carbon literacy climate crisis education media coverage popular culture fiction art games public opinion adaptation resilience vulnerability disaster risk reduction ecosystem-based adaptation flood control politics history political economy climate governance climate movement denial global warming controversy litigation individual actions unfccc un conferences kyoto protocol paris agreement portal glossary index the effects of climate change on mental health and well-being can be negative, especially for vulnerable populations and those with pre-existing serious mental illness. there are three broad pathways by which these effects can take place: directly, indirectly or via awareness. the direct pathway includes stress related conditions being caused by exposure to extreme weather events, such as post-traumatic stress disorder (ptsd). scientific studies have linked mental health outcomes to several climate-related exposures—heat, humidity, rainfall, drought, wildfires and floods. the indirect pathway can be via disruption to economic and social activities, such as when an area of farmland is less able to produce food. the third pathway can be of mere awareness of the climate change threat, even by individuals who are not otherwise affected by it. mental health outcomes have been measured in several studies through indicators such as psychiatric hospital admissions, mortality, self-harm and suicide rates. vulnerable populations and life stages include people with pre-existing mental illness, indigenous peoples, children and adolescents. the emotional responses to the threat of climate change can include eco-anxiety, ecological grief and eco-anger. such emotions can be rational responses to the degradation of the natural world and lead to adaptive action. assessing the exact mental health effects of climate change is difficult; increases in heat extremes pose risks to mental health which can manifest themselves in increased mental health-related hospital admissions and suicidality.: 9 impacts caused by heat impacts of higher global temperatures will have ramifications for the following aspects: vulnerability to extremes of heat, exposure of vulnerable populations to heatwaves, heat and physical activity, change in labor capacity, heat and sentiment (mental health), heat-related mortality. the global average and combined land and ocean surface temperature show a warming of 1.09 °c (range: 0.95 to 1.20 °c) from 1850–1900 to 2011–2020, based on multiple independently produced datasets. the trend is faster since 1970s than in any other 50-year period over at least the last 2000 years. heat-related health impacts for vulnerable people further information: effects of climate change § heatwaves, and heat illness vulnerable people with regard to heat illnesses include people with low incomes, minority groups, women (in particular pregnant women), children, older adults (over 65 years old), people with chronic diseases, disabilities and co-morbidities.: 13 further people at risk include those in urban environments (due to the urban heat island effect), outdoor workers and people who take certain prescription drugs. exposure to extreme heat poses an acute health hazard for many of the people deemed as vulnerable. climate change increases the frequency and severity of heatwaves and thus heat stress for people. human responses to heat stress can include heat stroke and hyperthermia. extreme heat is also linked to low quality sleep, acute kidney injury and complications with pregnancy. furthermore, it may cause the deterioration of pre-existing cardiovascular and respiratory disease.: 1624 adverse pregnancy outcomes due to high ambient temperatures include for example low birth weight and pre-term birth.: 1051 heat waves have also resulted in epidemics of chronic kidney disease (ckd). prolonged heat exposure, physical exertion, and dehydration are sufficient factors for the development of ckd. the human body requires evaporative cooling to prevent overheating, even with a low activity level. with excessive ambient heat and humidity during heatwaves, adequate evaporative cooling might be compromised. a wet-bulb temperature that is too high means that human bodies would no longer be able to adequately cool the skin. a wet bulb temperature of 35 °c is regarded as the limit for humans (called the "physiological threshold for human adaptability" to heat and humidity).: 1498 as of 2020, only two weather stations had recorded 35 °c wet-bulb temperatures, and only very briefly, but the frequency and duration of these events is expected to rise with ongoing climate change. global warming above 1.5 degrees risks making parts of the tropics uninhabitable because the threshold for the wet bulb temperature may be passed. people with cognitive health issues (e.g. depression, dementia, parkinson's disease) are more at risk when faced with high temperatures and ought to be extra careful. as cognitive performance has been shown to be differentially affected by heat. people with diabetes, are overweight, have sleep deprivation, or have cardiovascular/cerebrovascular conditions should avoid too much heat exposure. the risk of dying from chronic lung disease during a heat wave has been estimated at 1.8-8.2% higher compared to average summer temperatures. an 8% increase in hospitalization rate for people with copd has been estimated for every 1 °c increase in temperatures above 29 °c. in urban areas increasing heat waves are one effect of climate change that impacts human health: illustration of urban heat exposure via a temperature distribution map: red shows warm areas, white shows hot areas. the effects of heatwaves tend to be more pronounced in urban areas because they are typically warmer than surrounding rural areas due to the urban heat island effect.: 2926 this is caused from the way many cities are built. for example, they often have extensive areas of asphalt, reduced greenery along with many large heat-retaining buildings that physically block cooling breezes and ventilation. lack of water features are another cause.: 2926 extreme heat exposure in cities with a wet bulb globe temperature above 30 °c tripled between 1983 and 2016. it increased by about 50% when the population growth in these cities is not taken into account. cities are often on the front-line of climate impacts due to their densely concentrated populations, the urban heat island effect, their frequent proximity to coasts and waterways, and reliance on ageing physical infrastructure networks. heat-related mortality health experts warn that "exposure to extreme heat increases the risk of death from cardiovascular, cerebrovascular, and respiratory conditions and all-cause mortality. heat-related deaths in people older than 65 years reached a record high of an estimated 345 000 deaths in 2019".: 9 more than 70,000 europeans died as a result of the 2003 european heat wave. also more than 2,000 people died in karachi, pakistan in june 2015 due to a severe heat wave with temperatures as high as 49 °c (120 °f). estimates from 2020 found that more than 1300 people die in the united states every year as a result of exposure to extreme heat. increasing access to indoor cooling (air conditioning) will help