As 2025 draws to a close, it is confirmed as the second hottest year on record, surpassed only by 2024. This trend of extreme warming highlights a troubling pattern, as the last three years have consistently registered temperatures more than 1.5 degrees Celsius above preindustrial levels. These figures indicate a temporary breach of an international target aimed at limiting global warming, according to the Copernicus Climate Change Service.
The surge in temperatures has exceeded expectations set by climate models, leaving scientists grappling for answers. Various factors have been explored in an attempt to understand this unprecedented warming, including a significant volcanic eruption in the South Pacific and changes in pollution levels that typically block sunlight.
Potential Factors Behind the Warming Surge
In a recent analysis published by climate scientist Zeke Hausfather in Carbon Brief, four main contributors to the recent temperature increase were examined. The first of these was the 2022 eruption of Hunga Tonga–Hunga Ha‘apai, an underwater volcano responsible for releasing a massive plume of heat-trapping water vapor into the upper atmosphere.
The second factor identified was a recent uptick in solar output. While the timing of this increase correlates with the observed spike in temperatures, Hausfather notes that these two elements alone can only account for less than half of the rise.
The third contributor is the formation of a powerful El Niño phenomenon in late 2023, which involves warm waters accumulating in the eastern Pacific and subsequently driving global temperatures higher. Although El Niño can explain the exceptional warmth observed in 2024, it does not account for the significant temperature increases noted in early 2023.
Lastly, a notable decline in emissions of sulfur dioxide has emerged as a critical factor. This pollutant, primarily released from coal-fired power plants, acts to cool the planet by blocking sunlight. The reduction in sulfur dioxide emissions has been substantial, with a decrease of 40 percent over the past 18 years, largely due to pollution control measures in various countries, particularly China. In addition, a new international regulation introduced in 2020 has reduced sulfur dioxide emissions from cargo ships, leading to a significant drop in shipping pollution.
Shipping Pollution and Temperature Insights
While research generally suggests that reductions in shipping pollution have had only a modest impact on global temperatures, a study by James Hansen, the former chief climate scientist at NASA, posits that the decrease in shipping emissions may explain nearly all of the recent and exceptional warming. Hausfather acknowledges that collectively, these four factors could account for the surge in temperatures. Yet, he raises important questions about the implications of these findings.
Is this warming trend temporary, or does it signal an acceleration in global warming? The answer remains uncertain, underscoring the need for continued research and monitoring of climate dynamics. As the world grapples with these significant changes, the implications for ecosystems, weather patterns, and global policies are profound and warrant urgent attention.
