# Global expansion of extreme heat seasons > Situation record from CLSTR: https://clstr.news/situations/global-expansion-of-extreme-heat-seasons > Updated: 2026-10-05T11:08:00.000Z. Sources: 6. Developments: 2. Research indicates that climate change is altering traditional seasonal boundaries, causing extreme heat waves to extend beyond typical summer months. In regions such as Catalonia, September temperatures have reached levels previously considered normal for July, with multiple months recording absolute temperature records. A study published in Nature Climate Change shows that between 1979 and 2023, the global extreme heat season expanded by approximately 39 days. This shift occurred as the first heat waves of the year arrived about 15 days earlier and the final heat waves occurred roughly 24 days later. This trend is nearly universal, with 92.1% of land areas experiencing an increase in the duration of the season susceptible to heat waves. In urban environments like Mexico City, these rising temperatures are further intensified by urban heat islands, where materials such as concrete and asphalt exacerbate evaporation and water stress. Experts suggest that mitigation will require shifts toward green infrastructure and bioclimatic design. ## Timeline ### 2026-10-05: Global extreme heat season expands by 39 days over four decades Research shows the global extreme heat season has expanded by approximately 39 days since 1979, with heat waves starting earlier and ending later, intensifying urban heat island effects. 2 sources. https://clstr.news/cluster/global-extreme-heat-season-expands-by-39-days-over-four-decades ### 2026-09-25: Climate change extends extreme heat waves beyond summer months NASA research and recent temperature data show that climate change is extending extreme heat waves beyond summer, disrupting traditional seasonal patterns globally. 4 sources. https://clstr.news/cluster/climate-change-extends-extreme-heat-waves-beyond-summer-months --- Cite as: Global expansion of extreme heat seasons. CLSTR, https://clstr.news/situations/global-expansion-of-extreme-heat-seasons