Nicolas Borchers Arriagada

The Medical Journal of Australia ( MJA )– Lancet Countdown on health and climate change in Oceania was established in 2017 and produced its first regional assessment in 2018 and annual updates from 2019 to 2025. It examines five broad domains: (1) health hazards, exposures and impacts; (2) adaptation, planning and resilience for health; (3) mitigation actions and health co‐benefits; (4) economics and finance; and (5) public and political engagement. In this, the eighth report of the MJA – Lancet Countdown, we track an extensive suite of indicators across these five domains, accessing and presenting the latest data and further refining and developing our analyses. Our analyses show that exposure of infants and older adults to heatwaves in Australia and Aotearoa New Zealand has increased substantially over the past decade due to climate change, and half of the 16,230 young Australians aged 14–19 years surveyed reported that they are worried or sad about the impacts of climate change, including its threat to people, and about 1 in 7 reported that such feelings are negatively affecting their daily life. Increasing heat‐related mortality alone is placing a large economic burden on Australians, with associated inflation‐adjusted costs over the period 2021–2025 being more than double what they were at the start of the century, now averaging an estimated US$1.49 billion per year nationally. In other areas, some progress is being made. New Zealand's Health National Adaptation Plan 2024–2027, published in October 2024, lays the foundation for building climate resilience within its health system, while acknowledging the environmental and social determinants of health that apply more broadly. The provision of climate services to the health sector in both Australia and New Zealand is categorised as advanced. In Australia, healthcare‐related greenhouse gas emissions generally declined from 2016 to 2023. In conclusion, the threat to physical and mental health from climate change continues to grow. Despite pockets of progress, Australia and New Zealand have a long way to go to adequately mitigate and adapt to climate change, and in so doing not only avoid health impacts but seize the opportunity for generational health gains. Important opportunities have been lost, such as the failed attempts to amend Australia's Climate Change Act 2022 to ‘require decision‐makers to consider the health and well‐being of children in Australia when making significant decisions’. In 2026, Australia is in the spotlight as President of Negotiations for the United Nations Climate Change Conference (COP31)—an unprecedented opportunity for the Australian Government to push through the sizable step change in global climate action that is now critically required.

Combining Indigenous knowledge with scientific approaches can provide important insights into fire regime and landscape change. Using this approach, we recorded graphical and oral testimony of senior Indigenous fire manager from the Kune language group in central Arnhem Land who manages one of the few remaining traditionally managed savannas in Australia. The Indigenous fire manager reported that over his lifetime (c. 40 years) mid dry season fires have become more intense, harder to control, more ecologically harmful, and smokier, suggesting changes were associated with increased fuel loads. These observations were reinforced by analysis of satellite historical data around this estate, which showed increasing trends in end of growing season greenness, hotter, less humid mid-dry season (June-July) conditions, and more intense mid dry season fires. Collectively the cultural and scientific evidence shows that climate change can adversely affect Indigenous fire management. Therefore, historical knowledge of past Indigenous fire practices can only serve as a guide but not a blueprint for sustainable contemporary fire management. These findings suggest that programs design to restoring ’cultural burning’ to landscapes where these traditions have been disrupted by colonialism must be adaptive to accommodate the effects of climate change.

In a rapidly warming climate, heatwaves pose an increasing threat to human health. However, there is limited knowledge of heatwave impacts on health outcomes, or the role of humidity in the tropical and arid climates of Australia's Northern Territory (NT). Using a space‐time‐stratified case‐crossover design and conditional Poisson regression models, we analysed the association between heatwaves and emergency department (ED) presentations from 2001 to 2023, across all six NT public hospitals. Heatwaves were identified using the Excess Heat Factor (EHF) method, with both temperature‐only (heatwaves_T) and temperature‐plus‐humidity, heat‐index (heatwaves_TH) metrics. We undertook sub‐group analyses by sociodemographic characteristics and principal diagnosis. All‐cause ED presentations increased by 4.4% (RR = 1.044, 95%CI 1.018–1.071) for severe/extreme and 1.6% (RR = 1.016, 95%CI 1.002–1.030) for low‐intensity heatwaves_T. For heatwaves_TH, presentations increased by 6.1% (RR = 1.061, 95%CI 1.025–1.098, severe/extreme) and 0.9% (RR = 1.009, 95%CI 0.995–1.024, low‐intensity). Subpopulation increases for severe/extreme heatwaves_T occurred for ages 19–49 years (RR = 1.052; 95%CI 1.018–1.087), visitors (RR = 1.162, 95%CI 1.038–1.301) and skin conditions (RR = 1.116, 95%CI 1.048–1.189). Specific to severe/extreme heatwaves_TH, presentations increased for Aboriginal peoples (RR = 1.059, 95%CI 1.006–1.114), ages 50–64 years (RR = 1.141, 95%CI 1.059–1.230) and cardiovascular conditions (RR = 1.111, 95%CI 1.015–1.216). Comparing heatwave indexes, 57.1% of heatwave_T days were not captured by heatwave_TH, and conversely 49.6% of heatwaves_TH days were not captured by heatwave_T. These findings call for dual heatwave warning systems in the NT, incorporating both EHF temperature and heat‐index, and further humidity‐inclusive studies in varied climates. Preventative interventions should target high‐risk populations, prioritizing resources for severe and extreme heatwaves.

Fine particulate matter (PM_2.5) pollution related to biomass combustion is an established driver of poor health outcomes. While interventions such as face masks and portable air cleaners (PACs) reduce exposure, the health benefits and cost effectiveness of these interventions are not well understood. In this study, we modelled the benefits and costs of face masks and PACs across eight capital cities in Australia. We used historic daily PM_2.5 concentrations coupled with fire activity and temperature data to create a statistically representative year of data. We used established concentration–response functions for long-term exposure to PM_2.5 to estimate reductions in mortality risk and monetised them using the value of a statistical life. We calculated intervention costs by considering investment and operating expenses. We calculated the PM_2.5 reduction potential and the benefit–cost ratio (BCR) as measures to compare interventions, using Monte Carlo simulation to account for uncertainty. All interventions were found to have a BCR above 1. Despite being the least effective intervention for reducing personal PM_2.5 exposure, surgical masks, used for 3.6 h during smoky days, had the greatest BCR compared to P2/N95 masks, home-made PACs and branded PACs (BCR > 18.8 surgical masks; BCR > 3.7 P2/N95 masks; BCR > 1.8 home-made PACs; BCR > 1.4 branded PACs). This was due to the very low unit cost of surgical masks. Overall, the health benefits of using face masks and/or PACs outweighed the economic costs.

Adverse effects of non-optimal temperatures on mortality have been reported in different climates. However, only a low number of studies have been conducted in tropical locations where these effects might differ. Here, we estimate the association between ambient air temperature and all-cause mortality and assess the impact of non-optimal temperatures on attributable mortality at national and subnational levels in Colombia during 2010–2019. We obtained daily temperature and mortality data for 32 departments and conducted a two-stage analysis. In stage-1 we fitted a time-series Poisson model for each department and estimated the mortality-temperature association using distributed-lag-nonlinear models with 7–28 days of lag. In stage-2, we pooled these estimates using a multivariate meta-analytic model including mean temperature, relative humidity, and a multidimensional poverty index. We calculated attributable deaths and fractions due to non-optimal temperatures and due to overall heat and cold. We analyzed 2,561,561 deaths and found marked differences in exposure–response curves of mortality-temperature, where most departments showed acute heat effects but no cold effects for the 7-days lag. This lag-response curve for heat showed that the risk of death is higher during the same day (lag 0) of extreme temperatures and decreases after the third day. The country attributable fraction due to non-optimal temperature was higher for heat (1.77, 95% CI 1.16 – 2.31) during the 0–7 days lag, but higher for cold temperatures (4.68, 95% CI 2.34 – 6.72) during the 0–28 days lag. There was high heterogeneity in the estimated risks between departments. These results should inform planning adaptation strategies for climate change differentiated at subnational level.

Summary: The MJA–Lancet Countdown on health and climate change in Australia was established in 2017 and produced its first national assessment in 2018 and annual updates in 2019, 2020, 2021, 2022 and 2023. It examines five broad domains: health hazards, exposures and impacts; adaptation, planning and resilience for health; mitigation actions and health co‐benefits; economics and finance; and public and political engagement. In this, the seventh report of the MJA–Lancet Countdown, we track progress on an extensive suite of indicators across these five domains, accessing and presenting the latest data and further refining and developing our analyses. We also examine selected indicators of trends in health and climate change in New Zealand. Our analyses show the exposure to heatwaves is growing in Australia, increasing the risk of heat stress and other health threats such as bushfires and drought. Our analyses also highlight continuing deficiencies in Australia's response to the health and climate change threat. A key component of Australia's capacity to respond to bushfires, its number of firefighting volunteers, is in decline, dropping by 38 442 people (17%) in just seven years. Australia's total energy supply remains dominated by fossil fuels (coal, oil and natural gas), and although energy from coal decreased from 2021 to 2023, energy from oil increased, and transport energy from petrol grew substantially in 2021–22 (the most recent year for which data are available). Greenhouse gas emissions from Australia's health care sector in 2021 rose to their highest level since 2010. In other areas some progress is being made. The Australian Government completed the first pass of the National Climate Risk Assessment, which included health and social support as one of the eleven priority risks, based in part on the assessed severity of impact. Renewable sources such as wind and solar now provide almost 40% of Australia's electricity, with growth in both large‐scale and small‐scale (eg, household) renewable generation and battery storage systems. The sale of electric vehicles reached an all‐time high in 2023 of 98 436, accounting for 8.47% of all new vehicle sales. Although Australia had a reprieve from major catastrophic climate events in 2023, New Zealand experienced cyclone Gabrielle and unprecedented floods, which contributed to the highest displacement of people and insured economic losses over the period of our analyses (ie, since the year 2010 and 2000 respectively). Nationally, regionally and globally, the next five years are pivotal in reducing greenhouse gas emissions and transitioning energy production to renewables. Australia is now making progress in this direction. This progress must continue and accelerate, and the remaining deficiencies in Australia's response to the health and climate change threat must be addressed. There are strong signs that Australians are increasingly engaged and acting on health and climate change, and our new indicator on health and climate change litigation in Australia demonstrates the legal system is active on this issue in this country. Our 2022 and 2023 reports signalled our intentions to introduce indicators on Aboriginal and Torres Strait Islander health and climate change, and mental health and climate change in Australia. Although the development of appropriate indicators is challenging, these are key areas and we expect our reporting on them will commence in our next report.

Robust high spatiotemporal resolution daily PM_2.5 exposure estimates are limited in Australia. Estimates of daily PM_2.5 and the PM_2.5 component from extreme pollution events (e.g., bushfires and dust storms) are needed for epidemiological studies and health burden assessments attributable to these events. We sought to: (1) estimate daily PM_2.5 at a 5 km × 5 km spatial resolution across the Australian continent between 1 January 2001 and 30 June 2020 using a Random Forest (RF) algorithm, and (2) implement a seasonal-trend decomposition using loess (STL) methodology combined with selected statistical flags to identify extreme events and estimate the extreme pollution PM_2.5 component. We developed an RF model that achieved an out-of-bag R-squared of 71.5% and a root-mean-square error (RMSE) of 4.5 µg/m³. We predicted daily PM_2.5 across Australia, adequately capturing spatial and temporal variations. We showed how the STL method in combination with statistical flags can identify and quantify PM_2.5 attributable to extreme pollution events in different locations across the country.

Summary: TheMJA–LancetCountdown on health and climate change in Australia was established in 2017 and produced its first national assessment in 2018 and annual updates in 2019, 2020, 2021 and 2022. It examines five broad domains: health hazards, exposures and impacts; adaptation, planning and resilience for health; mitigation actions and health co‐benefits; economics and finance; and public and political engagement. In this, the sixth report of theMJA–LancetCountdown, we track progress on an extensive suite of indicators across these five domains, accessing and presenting the latest data and further refining and developing our analyses. Our results highlight the health and economic costs of inaction on health and climate change. A series of major flood events across the four eastern states of Australia in 2022 was the main contributor to insured losses from climate‐related catastrophes of $7.168 billion — the highest amount on record. The floods also directly caused 23 deaths and resulted in the displacement of tens of thousands of people. High red meat and processed meat consumption and insufficient consumption of fruit and vegetables accounted for about half of the 87 166 diet‐related deaths in Australia in 2021. Correction of this imbalance would both save lives and reduce the heavy carbon footprint associated with meat production. We find signs of progress on health and climate change. Importantly, the Australian Government released Australia's first National Health and Climate Strategy, and the Government of Western Australia is preparing a Health Sector Adaptation Plan. We also find increasing action on, and engagement with, health and climate change at a community level, with the number of electric vehicle sales almost doubling in 2022 compared with 2021, and with a 65% increase in coverage of health and climate change in the media in 2022 compared with 2021. Overall, the urgency of substantial enhancements in Australia's mitigation and adaptation responses to the enormous health and climate change challenge cannot be overstated. Australia's energy system, and its health care sector, currently emit an unreasonable and unjust proportion of greenhouse gases into the atmosphere. As theLancetCountdown enters its second and most critical phase in the leadup to 2030, the depth and breadth of our assessment of health and climate change will be augmented to increasingly examine Australia in its regional context, and to better measure and track key issues in Australia such as mental health and Aboriginal and Torres Strait Islander health and wellbeing.