Study warns world could face 57 more extremely hot days annually by 2100

A new study warns that by the end of the century, the world is set to experience nearly two additional months of dangerously hot “superhot” days each year.

With the poorest and smaller nations expected to bear the brunt far more than major carbon-emitting countries.

Researchers from World Weather Attribution and Climate Central used computer simulations to examine how climate action over the past decade, particularly the Paris Agreement, has influenced the frequency of extreme heat events. Without these measures, the world would have been on track for 114 extra superhot days annually. Thanks to mitigation efforts, that number is projected to be 57 days under a 2.6°C warming scenario by 2100. Under a high-emissions scenario of 4°C warming, the number of additional superhot days would nearly double.

The study defines superhot days as those hotter than 90% of comparable days between 1991 and 2020. Since 2015, the world has already added 11 superhot days on average. These extreme temperatures are associated with increased hospitalisations and deaths, with tens of thousands to millions of people potentially affected annually in the coming decades.

Recent events highlight the trend: last year’s weeklong heat wave in southern Europe is now 70% more likely and 0.6°C hotter than it would have been a decade ago. Future heat waves could be even more extreme, with projections showing increases of up to 3°C in Europe and 1.7°C in parts of the US and Mexico by century’s end.

The study also highlights the stark global inequality in climate impacts. The countries expected to see the largest increase in superhot days are mostly small, ocean-dependent nations, including the Solomon Islands, Samoa, Panama, and Indonesia. For example, Panama could face 149 additional superhot days annually, despite contributing only 1% of global carbon emissions. By contrast, major polluters like the US, China, and India, responsible for 42% of emissions, are projected to see just 23–30 extra superhot days.

Experts warn that even with current mitigation efforts, billions of people face a perilous future. “Global warming is driving yet another wedge between have and have-not nations; this will ultimately sow seeds of further geopolitical instability,” said climate scientist Andrew Weaver. Potsdam Climate Institute Director Johan Rockstrom added that staying below 4°C warming is far from enough to prevent catastrophic consequences.

The study underscores the urgent need for stronger climate action worldwide, not only to limit the number of superhot days but also to address the inequitable distribution of climate impacts across the globe.