Climate change has killed 4 million people since 2000 — and that’s an underestimate

In the early 2000s, when climate denialism was infiltrating political institutions worldwide, Australian epidemiologist Anthony McMichael undertook an unusual scientific inquiry: How many lives were being taken by climate change? His research team calculated the number of deaths from diarrheal disease, malnutrition, malaria, heat-related illness, and flooding in the year 2000, then used computer modeling to determine the percentage of those deaths caused by climate change. They estimated climate change was responsible for 166,000 lives lost that year. Fast-forward two decades and it’s clear that the impacts of rising temperatures can no longer be ignored. Climate research has progressed significantly, yet few studies have been done to determine how many people are currently dying due to the climate crisis. This week, a climate and health researcher published a commentary in Nature Medicine, taking the McMichael standard to its logical conclusion. Dr. Colin Carlson, a global change biologist and Georgetown University assistant professor, stated that by the end of 2022, climate change will have killed around 4 million people worldwide. That’s more than the population of Los Angeles or Berlin, “more than every other non-COVID public health emergency the World Health Organization has ever declared combined,” said Carlson. These deaths are still underestimated, as the McMichael standard doesn’t account for the deaths related to non-malarial diseases spread by mosquitoes, bacteria and fungal spores, ticks, and related health consequences of extreme weather. Wael Al-Delaimy, a multidisciplinary epidemiologist at the University of California, San Diego, admitted that the 4 million deaths since 2000 is “definitely an underestimate,” primarily due to the lack of mortality data in low- and middle-income countries. Researchers try to use attribution science to understand how climate change has influenced mortality, but this is often limited by a lack of quality mortality data. To move forward, Dr. Carlson suggested that predictive computer modeling could be used to simulate disease spread and climate conditions and predict changes in patterns. This approach could provide a more accurate climate mortality estimate than the McMichael standard. The impacts of climate change are visible and in need of urgent consideration to manage the evolving crisis.