Climate, extreme heat and human health: risks and lessons for Australia

Recent climate‐related heat events in the Northern Hemisphere are part of a global trend with immediate and long term implications for Australia’s health system

    We have a climate on steroids.
    Will Steffen, 2013

The Earth’s climate is changing inexorably, with widespread impacts on the environment and human health.1 As energy is pumped into the atmosphere from the burning of fossil fuels, greenhouse gas concentrations rise and global heating occurs. The most recent report from the Intergovernmental Panel on Climate Change (IPCC) clearly outlines the extent of human contribution and the widespread impacts across all parts of the globe.2 Extreme weather events such as heatwaves, heavy precipitation, droughts and cyclones are increasing in frequency and/or intensity, together with associated hazards, including bushfires, severe storms, and floods.2,3

The recent exceptional heatwave in North America’s Pacific Northwest region has been as dramatic and shocking as the bushfires in eastern Australia over the summer of 2019–2020. A series of temperature records has been set, with cascading effects across a wide area of the United States and Canada.4 For example, the temperature record for Lytton in British Columbia was broken on three successive days (27–29 June 2021), with the temperature finally reaching 49.6°C, 4.6°C higher than the pre‐heatwave record. Days later, wildfires destroyed the town. The heatwave led to over 500 unexpected and potentially preventable deaths in British Columbia, and approximately 200 further deaths in the American states of Washington and Oregon, many in older people.5

Early summer heat records have also been comprehensively broken in recent months across other parts of the Northern Hemisphere, from Russia and Eastern Europe to the Arabian peninsula, and from north Africa across to India.4 Vulnerability to such heat extremes is tracked through the Lancet Countdown international collaboration, and has been rising in every region of the world, as measured by a standardised index that incorporates heat exposure and health system capacity, even before the latest events.1 Health effects are not distributed equally. Vulnerability can be at an individual level, such as in the young, in older people, or in those with pre‐existing chronic health conditions. It can also be at a population level in socially and economically disadvantaged groups, or at a geographic level, for those living in climatic regions with more extreme weather.

Australia is the driest inhabited continent, and is highly vulnerable to the impacts of global warming.3 Long term meteorological data show an incremental and progressive rise in surface, ocean and atmospheric temperatures, with the climate warming on average by 1.4°C since 1910.3 The year 2019 was the hottest in Australia’s history, and each decade since 1980 has been warmer than the last.

As the average temperature rises, heat extremes will occur with increasing frequency and will have a dramatic impact on human health. Extreme heat exacerbates pre‐existing conditions such as cardiovascular and renal diseases, as well as directly leading to heat stroke.6 Heatwaves have already caused more deaths in Australia than all other natural hazards combined.7 Australia has led the way in developing indicators of heatwave intensity and adaptation capacity — the “excess heat factor” and “fire danger index”.6 However, more precise understandings of the complex indirect pathways leading from extreme heat to health impacts — including adverse biophysiological, behavioural and mental health impacts, and how they can be prevented — have yet to be developed.

People living and working in Australia’s vast tropical areas are particularly susceptible to the immediate impacts of extreme heat. For example, in the Northern Territory, temperatures in the period from December 2019 to January 2020 were almost 4°C higher than the long term average, and this change in climatic conditions is now having implications for medical workforce stability.8 Such findings are also likely to be applicable to northern parts of Western Australia and Queensland.

Heat is also an issue in temperate climates, as underprepared societies and systems often fail to provide a suitable built environment and the practical supports for people to adapt and cope with sudden heat events. For example, in Tasmania, for the period 2008–2016, research clearly identified the link between heat and morbidity, demonstrating a whole‐of‐population increase in emergency department presentations during heatwaves, and showing that those with vulnerability due to age, particularly children, were more likely to require acute health care services.9 Heatwave and health impact research is unevenly distributed across the globe, with a particular need for more research in countries and regions at greatest risk of adverse human health outcomes, mainly poorer countries in tropical and equatorial regions where 40% of the world’s population lives.10 Although we see poor health outcomes from extreme heat in hot, dry climates, the health impact of heat is strongly influenced by humidity, as high humidity hinders the evaporation of sweat, critical to cooling. Failure of thermoregulation can lead to heat stress and heat stroke. If we fail to limit global warming to under 1.5°C, modelling using temperature–humidity metrics predicts some tropical regions may become unliveable, as there is a limit to human adaptation.11 More research is needed at the interface of climate science, human physiology and adaptation, both behavioural and environmental.

Any extreme heat event, wherever it occurs in the world, attracts media and public attention, and quickens public appetite for more urgent climate action. The question of attribution of single weather events to longer term climate change is methodologically complex, but rapid attribution methods are being developed and have already been applied to demonstrate that the Pacific Northwest heatwave was virtually impossible without human‐induced global warming.12

Temperature records are now being broken frequently and by whole degrees, not tenths of degrees. This has led some atmospheric scientists to argue that the onus of scientific proof can now be reversed, requiring us to posit a null hypothesis that climate change is a causative factor for any single heatwave, which remains true unless proven otherwise.13

What specific lessons, risks and mitigation strategies are there for Australia?

First, we have an absolute obligation to behave as responsible global citizens and join with other countries to urgently reduce carbon emissions and limit global warming to less than 1.5°C. Agreeing how best to do that is the task that has continually eluded us in Australia, and which we are facing again in the run‐up to the Glasgow climate talks (COP26) in November 2021 (https://ukcop26.org/). Agreeing on net zero by 2050 will not be enough now; we have to demonstrate actual progress over the next decade and agree on more ambitious 2030 targets.

Second, we should note that the Australian health care sector was estimated as contributing 7% of Australia’s total carbon dioxide equivalent emissions for the financial year 2014–2015.14 However, the Australian Government has failed to include or integrate any mention of health within its broader national climate commitments.15 Our profession needs to be a leader in climate mitigation and, in coming years, the health sector will need to decarbonise at least as fast as other sectors. If we lag behind, this will increase the burden on other sectors.

Third, to be effective advocates, we need to continue to frame climate change as a health issue, first and foremost. Heat (as well as air pollution) is a good starting point for such a conversation, as the public has first‐hand experience of its effects. As trusted voices, health leaders can lead a public conversation to convey the links between climate change, heatwaves, and heat‐related deaths, which are more tangible than for many other climate, environment and health issues. Public health leaders, in particular, can also use heat health examples to speak about the underlying social determinants of health and their impact in different groups, making clear the importance of equity and the inseparability of climate health from climate justice.

Fourth, extreme weather events and the most recent IPCC report have further strengthened arguments for a national climate and health strategy, including an evidence‐based heat adaptation strategy and enhanced surveillance. All levels of government (national, state and local) should have a defined role as for other hazards. Early warning systems should be linked to local heat health action plans that identify specific settings, such as urban heat islands, and prioritise communication with vulnerable groups as to the most robust and evidence‐based strategies and actions for reducing personal heat exposure. The evidence base for these actions needs to be derived from an interdisciplinary and multisector approach that goes above and beyond epidemiological methods to include systems thinking and codesign of community‐led projects. This is required for all capital cities as well as rural and remote areas, and both tropical and temperate parts of Australia.