ACS Is Innovating for Health & Environment

According to Copernicus, the European Union’s climate change monitoring service, 2025 recorded as the third-warmest year ever recorded. Last year was only slightly cooler than 2023 and 2024—the warmest year on record. The past 11 years have been the 11 warmest on record, according to Copernicus data. In 2025, the average global temperature was about 2.65 degrees Fahrenheit higher than from 1850 to 1900—the period scientists use as a reference point, since it precedes the industrial era in which massive amounts of carbon pollution have been pumped into the atmosphere. Air temperature over global land areas was the second warmest last year, while the Antarctic saw its warmest annual temperature on record and the Arctic its second warmest. The last three years, 2023-2025, were exceptionally warm for two main reasons, Copernicus explained. The first is the build-up of greenhouse gases in the atmosphere from continued emissions and reduced uptake of carbon dioxide by natural sinks. Secondly, sea-surface temperatures reached exceptionally high levels across the ocean, associated with an El Niño event and other ocean variability factors, amplified by climate change. Additional factors include changes in the amounts of aerosols and clouds, and variations in atmospheric circulation. As in 2023 and 2024, a significant fraction of the globe was much warmer than average in 2025. Air and sea surface temperatures in the tropics were lower than in 2023 and 2024, yet still much above average in many areas outside of the tropics. The lower tropical temperatures compared to 2023-2024 were partly due to the persistence of near-average or weak La Niña conditions in the equatorial Pacific throughout 2025. Temperatures over the tropical Atlantic and Indian Ocean were also less extreme in 2025 than in 2024. "The fact that the last eleven years were the warmest on record provides further evidence of the unmistakable trend towards a hotter climate,” said Carlo Buontempo, Copernicus Climate Change Service director. “The world is rapidly approaching the long-term temperature limit set by the Paris agreement. We are bound to pass it; the choice we now have is how to best manage the inevitable overshoot and its consequences on societies and natural systems.” In 2025, half of the global land area experienced more days than average with at least strong heat stress—defined as feels-like temperature of 32°C or above. Heat stress is recognized by the World Health Organization as the leading cause of global weather-related deaths. In areas with dry and often windy conditions, high temperatures also contributed to the spread and intensification of exceptional wildfires, which produce carbon, toxic air pollutants like particulate matter, and ozone, which also impacts human health. These emissions significantly degraded air quality and had potentially harmful impacts on human health at both the local and larger scales in both North America and Europe.

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ACS Is Innovating for Health & Environment

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