Greece’s capital Athens is among the three top European cities with excess deaths in summer 2025, a study on heat mortality by the Grantham Institute has found.
Among the 30 European capitals assessed, Athens recorded 1,093 excess deaths, with 630 attributed to climate change and a climate-attributable share of 58%, placing Athens among the top three most affected urban centers.
At the country level, Greece ranked alongside Croatia and Bulgaria for the highest age-standardized excess mortality due to heat, underscoring the disproportionate impact on southern and southeastern Europe.
The study examined 854 cities (EU and affiliated countries, including the UK and Switzerland) with populations over 50,000—covering about 30% of Europe’s population—to estimate heat-related excess deaths in June–August 2025 and the share attributable to human-induced climate change.
Across those cities, there were 24,404 excess deaths and 68% (16,469 deaths) of these were attributable to climate change.
Europe showed a northwest–southeast gradient: central, southern and eastern regions warmed more than the north, aligning with where mortality was highest.
Among capitals, Rome, Athens and Bucharest had the highest standardized excess mortality per million, while Stockholm, Madrid and Bratislava showed the largest climate-attributable shares (greater than 85%).
Heat levels in 2025
Summer 2025 was the fourth warmest on record, 0.9°C above the 1990–2020 mean. Using observations and models, the report estimates that European summer temperatures are now 1.5–2.9°C higher than they would be in a world 1.3°C cooler (pre-industrial baseline).
Researchers used ERA5 temperatures and established exposure–response relationships (1990–2019) to estimate excess mortality under observed conditions and under a counterfactual 1.3°C cooler climate; the difference isolates the climate-change-attributable deaths.
The report notes that earlier Europe-wide (2022) and global (2023) studies found more than 50% of heat-related deaths attributable to climate change. This analysis finds 68%, however, which the authors say is attributable to the study’s focus on urban areas, where warming is greater due to the urban island effect.
