Rising global temperatures are probably the most recognised feature of global warming. So far average global temperatures have risen by 1.1 -1.2 C.

But this is a global average over all of the Earth’s surface and overtime, it does not convey what is happening at either regionally or at shorter intervals. There has been far greater increase over land and at high latitudes, seasonal differences and short term variability. 

All of these factors affect exposure to generally higher and extreme temperatures and therefore gtemperature related health and environmental impacts.

As discussed in this section, heat exposure is a powerful determinant of health and at in warmer regions has been described as a 'silent killer.' Heatwaves in Australia, for example, have resulted in more deaths than all other natural disasters combined. 

Key messages:

• Exposure to very high temperatures can result in heat exhaustion and heat stroke, but the vast majoroity of health impacts occur at exposure to temperatures in ranges that are not considered exceptional from destabilising underlying illness or vulnerability
• The are also absolute temperature thresholds at which humans (and other species) cannot survive. Many parts of the world are now close to, or even exceeding, these limits during hotter months
• Some groups are far more sensitive to heat than others: the elderly and those with existing chronic illness, children, pregnant women and unborn children, outdoor workers, for example.
• Adaptation to cold temperatures, both physiologically and behaviorally, is more feasible, less costly and less inequitable than adaptations to heat.

Increasing heat exposure

Longer term average temeprature is a useful metric to show global change but it poorly describes heat expsoure that mediates health effects.

By looking at the frequency and range - or distribution - of temperatures the relationship to exposure is much clearer . Plotted on a graph these temperature data points are expressed as a “bell curve” (or normal distribution):

From the shift in this bell curve it is easy to see the non linear increrase in exposure to more high temperature and also to new (unoprecedented) heat extremes. Greater variability in climatic conditions, also a consequence of global warming, further increases the occurrence of extreme conditions.

Data from Australia’s Bureau of Meteorology demonstrate how the relatively small change in average temperature equates to a large change in extreme conditions - with an increase of 1.4C in mean temperature there has been a more than 400% increase in frequency of high summer temperature maxima:  

Health effects 

Whilst health impacts from high temperatures that lead to heat stroke and exhaustion are widely recognised, the effects of heat through the worsening of underlying medical conditions are generally not, despite being far more prevalent and occuring at much lower temperature threshold.

National mortality records in Australia suggest substantial underreporting of heat-related deaths. Recent resrearch indicate that official records underestimate this association by at least 50-fold, or 2% of all deaths. 

Heat exposure has a complex set of physiological effects on bodily systems. Heat sensitive medical conditions include; cardiac and respiratory diseases, stroke, renal failure and electrolyte imbalance, premature delivery and stillbirth, sepsis, mental health episodes including suicides. Some groups are far more vulnerable including the elderly, children and pregnant women, people with outdoor occupations and related to poor housing or homelessness.

Numerous studies have examined the relationship between ambient temperature with mortality and morbidity. They consistently find that optimal conditions for health occur in the low 20s (centigrade) and that mortality rises non-linearly with temperature. Increased mortality also correlates with cold temperature but it is less clear how much of this effect is mediated by other associated factors such as seasonal (winter) respiratory illnesses rather than temperature alone.  

 The threshold for heat related mortality and morbidity start at quite surprisingly low values. Heart attacks and cardiac arrests for example occur with increases in average daily temperatures in the high 20's:

Threshold temperatures for heart attacks (Melbourne, Victoria): The results of this study indicated that threshold temperatures of 30 °C for daily average temperature, and 27 °C for 3-day average temperatures were identified. Days exceeding these thresholds resulted in a 10% and 37.7% increase in AMI (heart attack) admissions respectively.

Mortality increases signifincatly during heatwaves. During the 2003 European heatwave there were an estimated 70,000 excess deaths. In Victoria 374 excess deaths were recorded during the 4 days over 40C that occured prior to the 2009 bushfires, an increase of 65% over the expected mortality rate.

A study to investigate the mortality during heatwaves in Australian metropolitan cities found consistent and significant increased mortality in response to heatwaves, with elderly, especially female (>75 years old) being particularly vulnerable. 

Mean temperature has been found to be a generally more reliable indicator of mortality than maximum and minimum temperature, though studies do demonstrate a rise in mortality when nightime minima do not fall below temepratures in the low to mid 20s.

Attribution and projections

Climate change is increasing heat exposure and the number of heat related deaths and illness. A recent Nature study found that 37% of warm season heat-related can be attributed to human-induced climate change.

Heatwave exposure in the over-65 population has risen due to a combination of increased heatwaves and aging populations. Globally, heat-related mortality in this group has increased by and estimated 53.7% from 2000 to 2018, reaching 296,000 deaths. 

Without adequate mitigation heatwaves will become more frequent, intense and of longer duration with heat related deaths projected to increase by 471% in Australia by 2080. 

Health effects of Air Pollution

The urban smogs of the early-mid 20th century were known to cause large scale acute respiratory illness and deaths. The health impacts were so significant that regulations were introduced to restrict or prevent burning coal and other hydrocarbons in cities and populated areas around the world.

However, it was not until the late 20th century, with the publication of two large US studies, that we understood long term exposure to air pollutants led to deaths from heart disease and lung cancer as well as respiratory diseases.

These effects are mediated through fine particulate matter, gaseous pollutants such as oxides of nitrogen and sulphur, carbon monoxide and ozone; all products of fossil fuel combustion.

Further research since has established that air pollution can damage every organ in our body and as well as heart and lung disease, stroke and lung cancer, and that particulate pollution is implicated in the development of type 2 diabetes, obesity systemic inflammation, dementia, premature births and low birth weight, depression and suicide . And these effects occur even at low concerntrations with no evidence of a safe lower level of exposure.

Globally over 8 million people die prematurely as a result of exposure to air pollution produced from fossil fuels  - oil, coal and gas - combustion. In Australia, between 2566 and 5000 deaths per year in Australia (1.6 - 3.0% of deaths) are attributable to air pollution. Air pollution reduces life expectancy of Australians with 29,000 lost years of life, mostly due to heart disease. 

Some groups are more vulnerable to the effects of air pollutioin; the elderly and people with existing chronic illness, children and pregnant women.

Links with climate change

Air quality is strongly interrelated with global warming. The burning of fossil fuels for energy generation and transport are the biggest contributor of both air pollutiants and anthropogenic greenhouse gas emissions.

Higher temperatures worsen air quality in several ways, particularly in our cities.

Higher temperatures in urban environments and higher levels of NOx (from car exhaust, gas and wood burnning) increase the formation of ground level ozone.

Changing climatic conditions increase aero allergen levels; the pollen season that cause asthma and hay fever is lengthening with higher levels of allergen, and higher humidity and flood events increase indoor exposure moulds.

Bushfire extent and intensity is increasing and the prescribed burns that attempt to reduce also worsens air pollution.

An estimated 417 deaths and over 3000 cardiac and respiratory related hospital admissions occurred as a result of smoke from the 2019 -20 eastern Australian bushfires.

Co-Benefits of mitigation

The flipside of this is that actions to reduce emissions form fossil fuel use also have immediate and significant benefits resulting from improved air quality.

This has been observed in action many times when combuston activities have reduced or been ceased.

During the 2008 Beijing Olympics, there was deacrease in cardiac and respiratory illness and increase in birthweight of children born during the 47 day period of reduced air pollution.

The US clean air act is estimated to have prevented 230,000 premature deaths in 2020. An analysis of the cost-benefits or the measures to reduce air pollution resulted in benefits exceeding costs by 30 to 1 

Mental health is a priority for action on climate change

Climate change is already worsening our mental health and well being in numerous ways - from anxiety, strress and sadness about the threats it poses to impacts occuring from exposure to extreme and changing conditions and their direct and indirect consequences on human and environmental systems. 

These changes are not only set to further increase in line with escalating climate change, but in many cases both human exposure and the consequent mental health impacts are cumulative and compounded by repeated exposure. 

As with many other evironmental stressors, children are especially vulnerable, experiencing higher rates of mental ill health in response to disasters and extreme events which can persistent or affect development with lifelong consequences. 

Addressing mental health is an area that is already underserviced. The demand that results from more disasters and extreme events and disruption that occurs to exisiting services is particularly problematic for adapatation to climate change.

Heat and extreme weather

As with many adverse physical illnesses, higher ambient temperatures worsen mental health and well being, with increase in anxiety, depression, irritability, aggression and violent behaviour, domestic violence and increased drug and alcohol use. Mental health related presentation to emergency departments increase during heatwaves.  A 2008 study in Adelaide found that mental health related admissions inreased above a threshold of 26.7C and that hospital admission were 7.3% higher when compared to non-hetwave periods.There is a clear relationship between suicide risk and high temperatures, and with humidity.  Younger age groups and women being more significantly affected by changes in humidity and heatwave counts than the rest of  the population.

There are well established links between floods, fires and cyclones as well as heatwaves with adverse mental ill health outcomes,, including PTSD, anxiety-related responses, persistent and severe mental health disorders.  Extreme weather events are also associated with increase in aggressive behavior, domestic violence and alcohol and substance abuse. Impacts range from mild to severe and can be short or long term.

Vulnerable groups

People with underlying mental health conditions and more at risk from heat and other extreme weather events. Medications used to treat psychiatric illness can interfere with heat regulation. There is a higher probabilty of dependence on supply and health infrastructure that can be compromised in extreme events. People with chronic mental illness are also more likely to be socially disadvantaged, have poor housing or be homeless and have othe co-morbidities - chronic illness and /or illicit drugs use and alcohol.

Studies have shown children are particularly vulnerable with higher incidence of behavioural and emotional disturbances following exposure.

Over 50% of children in affected communities were found to have PTSD type symptioms at 6 months after the 2003 Canberra bushfires.

Read more at DEA: "How Climate Change Affects Mental health in Australia"

Extreme weather events

According to the latest IPCC report (6th AR 2021) it is an "established fact" that human-caused greenhouse gaas emissions have led to an increased frequency and/or intensity of some weather and climate extremes. 

These extreme events are known to result in direct and indirect impacts to our physical and mental health. 

Heatwaves

It is virtually certain that the intensity and duration of hot weather and heatwaves  has increased in both frequency and duration

Exposure to high tempertures results in increased mortality and a range of serious adverse health outcomes including heart attacks, strokes, heart failure, premature births and stillbirths, mental health presentations and suicide (see Heat).

In Australia heatwaves have caused more deaths than all other extreme weather and natural disasters combined. During the 2009 heatwave in Victoria where 4 consecutive days exceeded 40C, there were 374 excess deaths, and increase of  62% over expected mortality for that period. Emergency department attendance roses by 46% over the three hottest days and there was a 2.8 fold increase cardiac arrests increased. Similar outcomes have been documented in otehr continents during heatwaves. 

Floods

As the climate warms flood events are expected to become more frequent and intense. Climate change is intensifying Earth's hydrological cycle; warmer air holds more moisture and increased evaporation results in more intense storms resulting in potential for heavier rainfall events. Whilst rainfall is variable over seasns and from year to year, changing weather patterns, glacial melting and sea level rise are all exacerbating flood risks.

Floods are known to result in physical and mental ill health through a variety of direct and indirect pathways. Immediate dangers include drowning, hypothermia, injury and electrocution. There are greater risks of diarrhoeal, vector and rodent borne diseases and respiratory and skin infections during and after flooding. Contamination and poinsoning can occur. Through disrpution of transport and energy infrastructure and directly adffecting health infrastructure, floods affect access and provision of health services leading to delayed and reduced access particuarly to urgent care. 

Damage to homes and buildings can make them unsafe and result in displacement, loss of shelter and economic hardship.  Residual dampness in buildings promotes mold, with exposure causing allergic disease and fungal infection. Food security can be compromised by spoilage and loss of refrigeration and, in the longer term, damage to crops. 

All of these factors, from the trauma of the event itself to the dislocation of communities, loss of income and poroperty and financial hardship as well as uncertinty and stress of insurance claims and recurrence, have mental health impacts. as with other disasters there are high rates of anxiety, depression and PTSD in people who have been affected by floods.

An economic assessment into the economic and social costs of natural disaters found the impacts found the economic costs of the Queensland floods of 2011 amounted to $14.1 billion of which $5.9 was attributable to mental health costs.

Some groups within the population are at higher risk of physical injury and of mental ill health and some communities are at higher risk.  As witth other weather disaters, children are more vulnerable, being more prone to physical injury and psychological trauma and due to their dependence on adults. Similarly people with chronic ilnnesses or disabilities that compromise their mobility or comprehension of environmental dangers. 

Communities in the developing world have less resilient infrastructure and access to emergency services and healthcare, often more at risk of food and water insecurity.

Bushfires

Warmer temperatures, more frequent and severe heatwaves, low rainfall, drier vegetation and soil are leading to longer bushfire seasons and greater fire risk. A warmer climate raises the chance of lightening as an ignition source. 

How does climate chantge affect bushfires - Climate council

22% of adults affected by the 2009 Victorian ( Black Saturday) bushfires had signs of anxiety anxiety or depression and 9.3% accessed counselling or specialist mental health services.

Children are worse affected. Half of children in communities exposed to the 2003 Canberra bushfire had symptoms of PTSD at 6 months. In drought affected area an increase in the risk for suicide also increases.

Climate change is increasing the risk of Infectious Diseases

Many infectious diseases are increasing in frequency and range as a consequence of climate change. Warmer conditions and greater variability, changing precipitation, relative humidity and worsened air quality can alter disease pathways and/or can enhance the reproduction, transmision and virulence of pathogens (disease-causing organisms) and populaiton, range and behaviour of disease vectors.

Recent assessments suggest over half of all known pathogens can be aggravated by climate change.

See more at this interactive website that allows users to explore 1,000 pathways of amplified spread: Traceable evidence of the impacts of climate change on pathogenic human diseases

Extreme weather events - heatwaves, storms, floods, drought and bushfires - can affect the incidence of respiratory iinfections.

Susceptibility to infectious diseases can also be increased through undermining of population health as a result in changes to nutritional status or disruption of vital infrastructure as a result of heat and extreme  weather events.  There is also the potential for new and re-emergent pathogens from melting permafrost. Scientists have discovered previoulsy undescribed viruses and dormant microoganisms.

For example, in 2016 for example, Anthrax, thought to iroginate from a previously long-buried frozen reindeer carcas, hospitlised 20 people in Siberia and the death of a 12 year old boy.

Vector borne diseases

Mosquitoes are responsible for transmitting a range of diseases responsible for a significant proportion of the global burden of disease and mortality, and particularly in young children. Warmer conditions and more variable precipitation promote mosquitoe reproduction and survival. Recent climatic changes have been a major driver in the transmission of mosquitoe borne disease such as Dengue which has seen a 30-fold increase in incidence over the last half century.

Mosquitoes breed rapidly when there is standing water, but they also concerntrate around limited water sources during droughts, increasing the likelihood of disease transmission.

In the US the number of reported illnesses from mosquito, tick and flea bites more than doubled between 2004 and 2018. The incidence of Lyme disease (US) has nearly doubled since 1990 and the geographic range of has explanded as has the abundance and range of deer ticks that transmit it. Studies implicate climate change has contributed to this spread.

Asian Shistosomiasis in limted by the thermal tolerance of the snail vector. Milder winters are implicated in the Northward spread of Scistosomiasis in China where the shift in potential transmission range puts an additional 20 million peopel at risk of infection.

Zoonotic diseases (animal origin or animal host)

Around 10,000 virus species are able to infect humans, most of which are currently confirned to animal species. The movement and relocation of wildlife has increased due to land clearing (deforestation), mostly for agriculture, and climate change. This increases the risk of "spillover" events where exisiting and novel pathogen 'jump' accross to humans directly or via an intermediary vector. Examples include Ebola, Rabies, Avian Influenza, MERS and SARS / Covid).

Interactions between environmental factors and infectious diseases can be complex. The outbreak of Hantavirus in 2000 was linked to a local surge in rodent population in turn due to a 2 -3 fold increase in rainfall, this occured on a background of habitat loss leading to closer proximity between the rodents and humans.

Water and Food borne infections

Warmer conditions, earlier onset of spring and alteration in rainfall can promote food and water borne diseases. The most common forms of bacterial gastroenteritis, Salmonella and Campylobacter, occur more frequently with higher ambient temperatures. In the developing world, there is strong evidence of correlation between Cholera outbreaks and climate related variables (low rainfall and warmer temperature).

Many Vibrio species are human and animal pathogens, the abundance of these marine organisms is promoted by warmer sea surface temperatures.  Illness usually occurs as a result of eating raw/undercooked seafood but can be directly contracted from contaminated water. The incidence of vibrio-related illness has been rising in recent years with unprecented outbreaks at higher lattitudes (eg Northern Europe).

Warmer marine and freshwater, changing salinity and higher CO2 levels, in combination with higher nutrient levels, are predicted to cause more intense and frequent algal blooms. These are directly harmful to humans and animals and create dead zones in water bodies.
 

Fungal diseases

Fungal pathogens have become more problematic as a consequence of environmental disruption due to climate change and may have resulted in entirely novel fungal diseases. Fungal infections pose a challenging problem as they are not vaccine preventable and there are very limited antimicrobial agents available.

Dampness from floods and higher atmospheric humidity result in mould growth in homes and other buildings. Mold exposure can cause a variety of respiratory conditions from mucosal and skin irritation to allergies, asthma and pneumonia with children and people with pre-exisiting illnesses being particularly vulnerable. Living in a moudly house increases your risk of having asthma by 240%. Exposure to mold is inequitous with poor housing and social disadvantage greatly increasing risk. Exposure is likely to increase with further warming but there may also be an increase in mould allergen production.

Everything is connected – what we do to the world comes back to affect us. From carbon emissions, plastic wastes, air pollution through to destruction of forests and marine life, our actions eventually come back to impact our health.

Whilst development and progress over the last century has led to significant gains in human health, it has come at a cost to the health of the planet.

• Biodiversity which underpins many of the ecological systems that human health is dependent on, is being lost at an unprecedented rate in human history.
• Rapid urbanization has profoundly affected global energy and water use; the availability of arable land; and air and water pollution.
• The industrialization of food systems has had significant consequences on pollinators, fisheries and wildlife, freshwater security, degradation of soil whilst delivering suboptimal nutrition and inequitable access.
• Globally, particulate air pollution has impacted health contributing to cardiovascular disease while man-made pollutants such as plastics are now ubiquitous in ocean and terrestrial water systems where they are now incorporated into the food chain.

There are limits to Earth’s capacity and resources that define a safe operating space for humanity.. Four of these parameters, biodiversity loss, deforestation, greenhouse gas emissions and flows of nitrogen and phosphorus have already been exceeded.

We need to embrace a planetary health perspective where we recognize our interconnectedness and dependence on the health of nature. This will require us to change current paradigms of healthcare that are extractive and unsustainable and recognise health as being embedded within social and environmental conditions.

The health sector is not only one of the most carbon intensive sectors but is also one with enormous waste. In our practices and in how we practice, we can make simple changes that make a difference. Green Practice Society is here to help you align your working life to one embracing a planetary health perspective.

Read more from the Planetary Health Alliance