Rising temperatures are set to push more people into Mexico’s emergency rooms, adding pressure and costs to a public health system that is already under strain. A new study led by CMCC researchers finds that hot days increase demand for urgent care, while cold days – somewhat counterintuitively – reduce emergency department visits, and that the relationship between temperature and morbidity rests on several overlooked channels, including behavioural and ecosystem dynamics.

As global temperatures rise, understanding how heat and cold affect the demand for urgent medical care is a pressing public-health question, especially in developing countries where data on this topic has been scarce. The research, titled “Emergency department visits and temperature: Evidence from Mexico”, analyses fourteen years of case-level records from public hospitals in Mexico between 2008 and 2022. By combining this administrative dataset with high-resolution weather data from the ERA5 reanalysis, the authors estimate how day-to-day changes in average temperature affect the number of emergency department visits in each municipality.

The team focuses on acute health shocks that lead people to seek urgent care, using a statistical model that compares days with different temperatures within the same municipality, month and year. This design allows them to isolate the effect of temperature itself from other seasonal or regional factors that influence health outcomes, making it one of the first studies to document a national-scale, causal link between temperature and emergency department visits in a developing country.

The results show a clear pattern: when daily average temperatures rise above 30 degrees Celsius, same-day emergency department visits increase by around 3.6% to 3.7% compared to days in the 20–25 degree range. In contrast, days colder than 10 degrees see a drop in emergency visits of about 9% on the same day. When the authors extend their analysis to a 30-day window after a cold spell, they find that this reduction in visits nearly doubles, reaching around 16%, suggesting that some care is delayed rather than avoided altogether.

“Hot days drive more people to emergency departments, while cold days counterintuitively reduce admissions,” says CMCC researcher and co-author of the study Francesco Colelli. “The effect of temperatures is essentially linear rather than concentrated only at the extremes and climate change will likely mean more emergency room visits, with a tangible cost to public health systems, even outside of episodes of extreme heat.”

These findings contrast with the U-shaped relationship between temperature and mortality, which the study also confirms in the Mexican data, where both very hot and very cold days raise death rates.

“Emergency visits drop sharply on cold days and keep falling over the following month, which tells us that families postpone care rather than stop getting sick,” says lead author of the study and CMCC researcher Luis Sarmiento. “That shifts the conversation from a purely epidemiological story, where cold simply causes more disease, toward an economic and behavioral one, where temperature also changes when and whether people seek care. Heat works through equally concrete channels. Hot days bring more bites and stings from venomous animals, more dengue as mosquitoes thrive, and more bacterial infections, likely from food that spoils faster in warm conditions. A changing climate will therefore reshape not only how much urgent care Mexico needs, but also who walks through the hospital door and why.”

Climate change will add pressure and costs

Using climate model projections, the study estimates how unmitigated climate change could affect Mexico’s emergency care system in the coming decades. Holding other factors constant, the authors project an increase in temperature-induced annual emergency department visits in Mexico by around 0.35% by midcentury, adding roughly 8.5 million USD per year in medical expenditures. A significant cost for a public health system that already faces capacity constraints and seasonal pressures.

By framing the temperature–morbidity relationship in economic terms and translating it into forward-looking cost estimates, the study offers policymakers a clearer picture of how climate change will affect day-to-day health service demand.

The study also finds that not all groups are affected equally. Children and teenagers emerge as the most sensitive age group, with stronger responses to both heat and cold than older adults. This reflects differences in the conditions that typically bring people to emergency departments.

“Morbidity has received far less attention than mortality in the climate-health literature, even though it captures a much broader and more immediate dimension of how a changing climate affects people’s daily lives,” says co-author of the study Filippo Pavanello. “Working with granular, nationwide hospital data from Mexico allowed us to move beyond extreme-event case studies and show that emergency care demand responds to temperature across its entire range. This helps us quantify a health cost of climate change that is currently invisible in most policy discussions, but that public healthcare systems will need to plan for.”

For more information:

Luis Sarmiento, Francesco Pietro Colelli, Filippo Pavanello, Emergency department visits and temperature: Evidence from Mexico, Journal of Economic Behavior & Organization, Volume 250, 2026, 107728, ISSN 0167-2681, https://doi.org/10.1016/j.jebo.2026.107728