2. Environmental Change and Human Health

• Climate change can increase the number and severity of extreme weather events, such as bushfires and floods. These events can have an adverse impact on human health.
• Increasing temperatures can affect the geographic spread of diseases — for example, by changing the distribution of mosquitoes and therefore of vector-borne diseases such as dengue fever or malaria.

Climate change is linked to increased exposure to extreme heat, with Australians experiencing a 35% increase in exposure to excessive heat over the period 2002 to 2022.^[1] Rapid rises in heat gain (due to hotter conditions) affect the body’s ability to regulate internal temperature and can result in illnesses such as heat cramp, heat exhaustion and heatstroke.^[2] Exposure to high temperatures can also lead to respiratory distress and dehydration (which can result in kidney disease), as well as exacerbating pre-existing conditions such as cardiovascular disease.^[3]

Climate change also increases the risk of extreme weather events, including floods and bushfires, the latter of which are a particular concern in Australia. Between 2013 and 2022, there was an increase in exposure to very high or extremely high bushfire danger, and the average annual exposure increased from 27.5 days per person to 33.6 days per person between 2003 and 2012.^[4] Bushfires can significantly impact human health, through direct exposure to fires (causing burns and unintentional injuries) or smoke.^[5] Smoke exposure and changes in air quality have impacts on people with pre-existing conditions such as asthma and chronic lung disease, with other vulnerable groups including the elderly, young children and pregnant women.^[6]

Apart from bushfires, there are many other sources of air pollution, most crucially from burning fossil fuels for transportation, energy and industrial production.^[7] Over 90% of the world’s urban population is exposed to air containing pollutants at levels that exceed WHO’s guidance.^[8] Chronic air pollution exposure (indoor and outdoor) has been identified by the WHO as the second leading cause of deaths from NCDs globally, being responsible for 26% of deaths from heart disease, 24% from stroke, 43% from chronic obstructive pulmonary disease and 29% from lung cancer.^[9] It is also linked to pregnancy complications and an increased incidence of low birthweight babies. Although Australia has a reputation for good air quality, an estimated 3,000 people die prematurely each year from air pollution.^[10] Climate change is linked to other environmental changes that affect air quality and cause respiratory health conditions, such as elevated levels of urban ozone during heatwaves, which can cause difficulties with breathing, as well as increasing susceptibility to lung infections and aggravating lung diseases such as asthma, chronic obstructive pulmonary disease and chronic bronchitis.^[11]

Exposure to climate-related disasters, such as bushfires, can cause psychological trauma and is linked to mental illnesses such as post-traumatic stress disorder, depression and anxiety.^[12] Bushfires can impact the short- and long-term mental health of firefighters, first responders, volunteers and members of affected communities.^[13] Climate change will also increase longer-term weather events such as drought, which is anticipated to lead to loss of life, disruption of relationships and displacement, which are associated with depression, chronic psychological stress and generalised anxiety. In Australia, farmers and rural communities are at particular risk, as they are increasingly exposed to environmental degradation, persistent drought and weather disasters, which are impacting productivity in the agricultural sector and the financial viability of many farms.^[14] Climate change also impacts mental health through more indirect pathways. First, it impacts physical health, with physical health problems causally and reciprocally related to the development of mental health problems, particularly in vulnerable groups such as older people and Indigenous people. Second, it disrupts economic relationships in communities, creating economic hardship and subsequent poor mental health, as well disrupting social cohesion, community participation and social relationships, which are all important to good mental health.^[15] Finally, people’s awareness and anticipation of the effects of climate change can have negative mental health impacts, with terms such as ‘ecoanxiety’ being used to describe feelings of hopelessness, anxiety and fear stemming from the awareness of climate change and environmental degradation.^[16]

A growing body of evidence links planetary warming to changes in the rate and distribution of infectious disease. Vector-borne infectious diseases (such as malaria and dengue fever), zoonotic diseases (such as H5N1 influenza carried by birds) and food-borne illnesses (such as salmonellosis) are highly sensitive to changes in environmental conditions.^[17] Increases in global temperature mean that mosquitos which act as disease vectors can live at higher latitudes and altitudes, introducing diseases such as malaria and dengue fever into new areas. Global warming lengthens the transmission season in areas where these diseases are already established,^[18] while increased rainfall and flooding events, combined with warmer weather, create ideal conditions for mosquito breeding, thus increasing the risk of disease outbreaks.^[19] Increases in the density and geographic range of some species (caused by climate-related ecosystem changes) may lead to a rise in the emergence of novel infectious diseases by amplifying pathogen populations and circulating mutations.^[20] Greater global connectivity and population growth also increase the interactions between humans and animals that act as disease reservoirs, compounding these effects.^[21] As illustrated by COVID-19, novel infectious diseases are particularly concerning because the human population does not have pre-existing natural immunity.^[22]