It is widely believed that climate change is the single biggest threat to human health. A global temperature increase of 2° Celsius—a threshold that will likely be exceeded by the end of the century—could claim as many as one billion lives, with extreme weather events, heatwaves, droughts, flooding, infectious disease outbreaks, and food shortages among the causes of death. But the situation may in fact be far worse because the current forecasts fail to account for the inevitable increase in antimicrobial resistance (AMR).

Climate change could have a profound effect on AMR, as evidence increasingly indicates that adverse weather and rising temperatures can facilitate the emergence and spread of drug-resistant pathogens. But models seeking to gauge the health effects of climate change disregard the growing risk of drug resistance, as do policy responses to global warming—a massive oversight that will hinder our ability to treat infections and keep people healthy.

Despite increasing the likelihood of extinction for nearly 11,000 species, a warmer planet could improve conditions for bacteria and fungi. Higher temperatures are associated with increased bacterial growth and infection rates, and can also put selective pressure on microbes to mutate and develop antibiotic resistance. One recent study in China found that each 1°C increase in air temperature was associated with a 14 percent increase in drug-resistant Klebsiella pneumoniae infections and a 6 percent increase in drug-resistant Pseudomonas aeruginosa infections.

Similarly, extreme weather, especially floods and droughts, will increase the spread of infectious diseases such as water-borne cholera and typhoid, as well as drug resistance. Such events often disrupt access to clean water and sanitation, making prevention and control of infection much more challenging. Moreover, urban density tends to accelerate the transmission of pathogens. According to some estimates, the climate crisis could displace 1.2 billion people by 2050, likely resulting in ever more crowded cities.

AMR is already recognised as an escalating global crisis. In 2019, it was associated with nearly five million deaths, making drug resistance one of the world’s biggest killers. The World Health Organisation has identified AMR as one of ten major threats to global health, alongside climate change, and world leaders are serious about addressing the problem, with a high-level meeting on AMR to be held on the sidelines of the United Nations General Assembly in September.

But many still think of AMR as distinct from global warming. For example, the latest Lancet Countdown report on health and climate change makes no mention of AMR, drug resistance, or antibiotics. Similarly, the Quadripartite Secretariat for One Health – comprising the Food and Agriculture Organization of the UN, the UN Environment Programme, the WHO, and the World Organisation for Animal Health— has failed to study the relationship between global warming and AMR, let alone how AMR will affect the health risks of climate change.

The international community is severely underestimating the impact of climate change on people’s health and our ability to treat them. To prepare for the mounting AMR crisis, we must increasingly rely on preventing and controlling infection, and, more importantly, ensure the judicious use of effective antibiotics. That will require developing new antibiotics, which are often unattractive for pharmaceutical companies, making the right investments and establishing the right incentives so that existing antibiotics reach the people who need them.

To this end, organisations like mine, the Global Antibiotic Research & Development Partnership, are encouraging the creation of new drugs and improving access to essential antibiotics already on the market, particularly in lower-income countries. Equitable antibiotic use and distribution will become increasingly important, because, as with climate change, it is the poorest communities that are usually hit hardest by AMR.

But that won’t be enough. Global policymakers must significantly increase funding for AMR research to ensure that they are ready to respond to new forms of drug resistance caused directly or indirectly by global warming. Doing so will require including AMR in climate-change contingencies and, more importantly, viewing drug resistance and rising temperatures as interconnected, rather than distinct, challenges, starting at the UN high-level meeting on AMR in September and this year’s UN Climate Change Conference (COP29) in Baku. Otherwise, the effectiveness of existing drugs will falter just when they are most needed.

—Project Syndicate