Heat-related deaths rise by 36% according to the Lancet Countdown

The 2026 report of the Lancet Countdown on Health and Climate Change, prepared by 146 researchers from more than 100 institutions in over 30 countries, with the World Health Organization as strategic collaborator, captures an acceleration of health damage linked to climate change. The most significant figure concerns 2023, when heat was associated with a record number of 710,000 deaths worldwide.

Of these deaths, more than 70% are attributable to human-caused climate change, according to the report. Since the Paris Agreement has been in force, the average annual number of deaths linked to high temperatures has risen by about 36% worldwide, an increase that the document associates with the intensification of heatwaves recorded in recent years.

The head of the WHO’s Climate Change and Health Unit, Diarmid Campbell-Lendrum, commented on the study’s findings as follows: “Climate change is already harming health in every region of the world.” A statement that forms part of a report built as a collective effort by more than one hundred research institutions, rather than as a single study.

For Italy, the report cites a specific figure: 82.7% of heatwave days recorded between 2021 and 2025 would not have occurred without the contribution of human-caused climate change. This is a percentage that places Italian territory among the areas where the attribution between global warming and local extreme events is, according to the document, particularly pronounced in the period considered.

The Lancet Countdown is a synthesis report that aggregates epidemiological data and climate attribution estimates collected from dozens of research groups coordinated on a global scale: not an experimental study on a defined sample, but a compilation of statistical analyses and attribution models linking observed heat events to long-term climate trends. The figures on deaths and heatwaves derive from modelling estimates — which measure an association between temperatures and mortality, not a direct causal link verifiable on a case-by-case basis — and the document itself highlights margins of uncertainty in projections for individual countries. The report does not disclose conflicts of interest among the groups involved. The figure of a 36% increase in heat-related deaths after the Paris Agreement remains, in this context, the summary indicator underpinning the call to consider the phenomenon a global public health priority.