The Lancet Countdown an international research collaboration that independently monitors the evolving impacts of climate change on health, and the emerging health opportunities of climate action highlights in its last report a world accelerating in a wrong direction. This 2023 report draws on the expertise of 114 scientists and health practitioners from 52 research institutions and UN agencies worldwide to provide its most comprehensive assessment yet.

In 2023, the world saw the highest global temperatures in over 100 000 years, and heat records were broken in all continents through 2022. Adults older than 65 years and infants younger than 1 year, for whom extreme heat can be particularly life-threatening, are now exposed to twice as many heatwave days as they would have experienced in 1986–2005. Harnessing the rapidly advancing science of detection and attribution, new analysis shows that over 60% of the days that reached health-threatening high temperatures in 2020 were made more than twice as likely to occur due to anthropogenic climate change; and heat-related deaths of people older than 65 years increased by 85% compared with 1990–2000, substantially higher than the 38% increase that would have been expected had temperatures not changed, underlines the Lancet Countdown.

The health risks of a 2°C hotter world underscore the health imperative of accelerating climate change action. With limits to adaptation drawing closer, ambitious mitigation is paramount to keep the magnitude of health hazards within the limits of the capacity of health systems to adapt. Yet years of scientific warnings of the threat to people’s lives have been met with  grossly insufficient action, and policies to date have put the world on track to almost 3°C of heating.

The growing threats experienced to date are early signs and symptoms of what a rapidly changing climate could mean for the health of the world’s populations. With 1337 tonnes of CO2 emitted each second, each moment of delay worsens the risks to people’s health and survival. In this year’s report, new projections reveal the dangers of further delays in action, with every tracked health dimension worsening as the climate changes. If global mean temperature continues to rise to just under 2°C, annual heat-related deaths are projected to increase by 370% by midcentury, assuming no substantial progress on adaptation.

Under such a scenario, heat-related labour loss is projected to increase by 50%), and heatwaves alone could lead to 524.9 million additional people experiencing moderate-to-severe food insecurity by 2041–60, aggravating the global risk of malnutrition. Life-threatening infectious diseases are also projected to spread further, with the length of coastline suitable for Vibrio pathogens expanding by 17–25%, and the transmission potential for dengue increasing by 36–37% by midcentury.

As risks rise, so will the costs and challenges of adaptation. These estimates provide some indication of what the future  could hold. However, poor  accounting for non-linear responses, tipping points, and cascading and synergistic interactions  could render these projections conservative, disproportionately increasing the threat to the health of populations worldwide.

Despite the challenges, data also expose the transformative health benefits that could come from the transition to a zero-carbon future, with health professionals playing a crucial role in ensuring these gains are maximised. Globally, 775 million people still live without electricity, and close to 1 billion people are still served by health-care facilities without reliable energy. With structural global inequities in the development of, access to, and use of clean energy, only 2.3% of electricity in low HDI countries comes from modern renewables.

In this context, the transition to renewables can enable access to decentralised clean energy and, coupled with interventions to increase energy efficiency, can reduce energy poverty and power high quality health-supportive services. By reducing the  burning of dirty fuels (including fossil fuels and biomass), such interventions could help avoid a large proportion of the 1.9 million deaths that occur annually from dirty-fuel-derived, outdoor, airborne,fine particulate matter pollution, and a large proportion of the 78 deaths per 100.000 people associated with exposure to indoor air pollution.   

On December 3, the COP28 negotiations in Dubai will host the first "health day" ever held at the climate negotiations. As the latest IPCC report highlights that climate change is a grave threat to human well-being and planetary health. It remains to be seen whether tangible and far-reaching measures will be decided.

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