Accelerating towards net zero emissions: the most important global health intervention.

During my time as Director-General of the WHO, we achieved a 62% reduction in the number of malaria deaths from 2000 to 2015, a 53% decrease in childhood mortality from 1990 to 2015, and extensive improvements in infection rates, mortality, and treatments in neglected tropical diseases. However, the greatest global health intervention is yet to be fully implemented. Climate change is already affecting the wellbeing of populations in every world region and, in the coming decades, could result in an annual global death toll in the hundreds of thousands and affect the health of hundreds of millions of people.

No population is left untouched. In the past year, Australia and western USA had the worst wildfire seasons in history, causing dozens of direct deaths, exposing millions to hazardous levels of air pollution, and showing that even high-income countries are not immune to the health effects of climate change. However, the greatest burden of the health effects of climate change is felt in low-income and middle-income countries—those that have contributed least to the problem and are least prepared to cope with its consequences. Furthermore, the most marginalised and vulnerable populations across all societies disproportionately bear this burden, widening existing gaps in health outcomes. Additionally, the COVID-19 pandemic, resulting from a zoonotic spillover event and exacerbated by existing environmental, health, and social inequities and extreme weather events, has at times overwhelmed even the strongest health systems. Furthermore, climate change and other environmental harms such as air pollution and deforestation increase the risk of future pandemics and leave the world vulnerable.

The mitigation of and adaptation to climate change must be ambitious and integrated into all actions to address the social determinants of health. Importantly, during my time with WHO, countries adopted the 2030 Agenda for Sustainable Development, with 17 goals and 169 targets to ensure that every person on the planet can thrive. We also saw the adoption of the Paris Agreement, which aims to keep the global temperature rise within safe limits and is the most important public health agreement of this century. Meeting the commitments of the Paris Agreement is essential to improving health and achieving the Sustainable Development Goals (SDGs), including ending hunger and malnutrition, ensuring universal health coverage and universal access to reliable clean energy, reducing the burden of non-communicable diseases, and improving mental health.

Now is the time to increase action on climate change at a global level. Countries are revising their climate change commitments in preparation for the next UN Climate Change Conference, COP26, in Glasgow November, 2021. These commitments, the Nationally Determined Contributions (NDCs), must be three times more ambitious to limit the global temperature rise to 2°C, and five times stronger to keep that limit to 1·5°C. Nothing short of net zero emissions by 2050 will keep us at 1·5°C this century. Without stronger commitments, we are on track for warming of greater than 3°C, a change that is untenable for the health of many populations.

Stronger climate change commitments can come with great improvements in population health, benefiting current and future generations. Ian Hamilton and colleagues studied the health benefits of the NDCs and the policies to implement them across nine countries that, combined, contribute to over 70% of the world's greenhouse gas emissions. If these countries adopted commitments consistent with the Paris Agreement and placed health at the centre of their climate policies, they could benefit from an annual reduction of 1·6 million air pollution-related deaths, 6·4 million diet-related deaths, and 2·1 million physical inactivity-related deaths by 2040. Such improvements contribute substantially to the SDG target to reduce deaths due to non-communicable diseases, which currently account for over 70% of deaths worldwide. These health benefits will outweigh the costs of mitigation policies, even without considering the longer-term health and economic benefits of avoiding more severe climate change.

The potential deaths avoided in relation to air pollution, diet, and physical inactivity are considerable across all countries and income settings studied, with China having among the greatest benefits across all three areas. In the other countries studied, the greatest benefits resulting from reductions in air pollution can be achieved in India and Indonesia. For diet-related deaths, the greatest benefits are seen in Germany and the USA. Additionally, considering deaths attributable to physical inactivity, the greatest benefits can be achieved in the USA, the UK, and South Africa.

These findings, along with the ongoing impacts of and response to the COVID-19 pandemic, underline the essential nature of a Health in All Policies approach. Such an approach involves adopting a health improvement framing into all policy decisions—avoiding harms to health and seeking synergies to improve population health and health equity.

With climate change action consistent with the Paris Agreement and a Health in All Policies approach to climate policies, the public health implications are overwhelmingly positive. Such interventions will reduce the burden of non-communicable diseases in the short term and climate-related risk factors in the long term, with the number of lives saved this century potentially in the hundreds of millions. Thus, achieving net zero emissions is the most important global health intervention now and for decades to come.

At the same time, it is essential that health and the Paris Agreement are central to all economic recovery measures; otherwise, we put public health and the economy at risk now and in the longer term by locking ourselves in to further climate change.

As countries revise their NDCs and continue to introduce economic stimulus measures to begin the process of recovery from the global pandemic, placing health at the core of all policies and at all levels of government across sectors will ensure the best possible health outcomes for current and future generations and help achieve the world's aim of limiting warming to 1·5°C.