The COVID-19 pandemic has further emphasised the inequalities in the world's capacity to respond to health emergencies. The pandemic is also unfolding in a world already struggling with the negative effects of the climate crisis, and the impact of COVID-19 on national economies could hamper efforts to implement measures to address global warming. In 2020 alone, record temperatures resulted in droughts, wildfires, reduced crop production, and a new high of 3·1 billion more person-days of heatwave exposure among people older than 65 years and 626 million more among children younger than 1 year, compared with the annual average for the 1986–2005 baseline. The climate crisis is the result of human activities (primarily the burning of fossil fuels) that have fundamentally increased the concentration of greenhouse gases in Earth's atmosphere. However, even with overwhelming evidence on the health impacts of climate change, countries are still not delivering responses proportionate to the rising risks their populations face.
The annual publication of The Lancet Countdown on health and climate change on Oct 20 preceded by a few days the 2021 UN Climate Change Conference (COP26) in Glasgow, UK, which will end after this Editorial has gone to press. COP26 aims to reach a consensus among political leaders to realise the ambition of the Paris Agreement to limit the global average temperature rise to 1·5°C and to mobilise the financial resources required for all countries to have an effective climate response. However, the urgency of tackling climate change requires rapid and broad actions that go beyond words.
The Lancet Countdown confirmed how climate change is impacting infectious diseases, with the spread of diseases, originally affecting only tropical settings in currently more temperate regions due to increased environmental suitability for the transmission of many water-borne, air-borne, food-borne, and vector-borne pathogens. For example, the number of months with environmentally suitable conditions for the transmission of malaria rose by 39% from 1950–59 to 2010–19 in densely populated highland areas in countries with a low human development index, threatening populations who had been comparatively safe from this disease so far. The epidemic potential for dengue virus, Zika virus, and chikungunya virus, which currently primarily affect populations in Central America, South America, the Caribbean, Africa, and south Asia, increased globally, with a basic reproductive rate increase of 13% for transmission by Aedes aegypti and 7% for transmission by Aedes albopictus compared with the 1950s. Even the environmental suitability for Vibrio cholerae, which causes almost 100 000 deaths annually, has expanded to the coastline of countries with a high development index that had traditionally not been affected by this pathogen.
Climate change weakens economies, affects primarily the poorest members of society, and impacts on the strength of health systems. The time left to reverse global warming is getting more and more limited. So far, some agreements have been reached at COP26, although concern remains about the fact that China, India, and the USA, three countries with high rates of carbon emissions, have not yet shown strong commitment to take drastic measures to tackle climate change. India's Prime Minister, Narendra Modi, pledged to reach net-zero carbon emissions by 2070, a date two decades beyond the target set by COP26 organisers, while China has made a pledge to reach carbon neutrality by 2060. On the hopeful side, more than 100 countries have committed to reverse deforestation by 2030; besides preserving the life-saving role of trees in reducing CO2 levels in the atmosphere, reducing deforestation could limit contact between people and wild animals and the potential for outbreaks of zoonoses. There has also been an agreement to phase out coal power in the 2030s for major economies, and the 2040s for poorer nations, but China, Russia, and the USA have not agreed so far.
Mitigation of the impact of the climate crisis is going to be the main challenge for the future of our planet. For infectious diseases, it will be important to build on the experience of COVID-19, which has shown that the capacity to rapidly develop and deploy vaccines and non-pharmaceutical measures at the global level is essential. Moreover, global networks for surveillance and monitoring of infectious diseases, especially zoonoses, will need to be strengthened to prevent and control future outbreaks. We cannot waste our last chances to take strong measures to limit the damage caused by the climate crisis.
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