The year 2025 is projected to conclude as the second hottest year on record, following only 2024. This trend continues a concerning pattern of increasing global temperatures, with the last three years marking the hottest ever recorded. According to the Copernicus Climate Change Service, each of these years has experienced temperatures more than 1.5 degrees Celsius above preindustrial levels, temporarily breaching international climate goals.
The surge in temperatures, which surpasses climate model predictions, has left scientists puzzled. Various factors have been proposed to explain this exceptional warming, ranging from a significant volcanic eruption to changes in pollution levels that typically block sunlight.
Potential Drivers of Recent Warming
In a detailed analysis for Carbon Brief, climate scientist Zeke Hausfather examined four primary contributors to the recent temperature rise. The first factor is the 2022 eruption of the Hunga Tonga–Hunga Ha‘apai volcano, located in the South Pacific. This event sent a substantial plume of heat-trapping water vapor into the upper atmosphere, contributing to warming.
The second factor is a recent increase in solar output. While the correlation with rising temperatures is notable, Hausfather asserts that these two factors alone account for less than half of the observed temperature increase.
A third aspect involves the emergence of a strong El Niño in late 2023, characterized by warm waters gathering in the eastern Pacific. Although this phenomenon may explain the exceptional warmth in 2024, Hausfather indicates it cannot account for the early temperature spikes in 2023.
The final consideration is the significant reduction in sulfur dioxide emissions, primarily from coal-fired power plants. Sulfur dioxide acts as a pollutant that cools the planet by blocking sunlight. Over the past 18 years, emissions of this pollutant have decreased by 40 percent, notably due to pollution control measures in countries like China. Additionally, a 2020 international regulation aimed at reducing sulfur dioxide from cargo ships has led to substantial declines in shipping-related pollution.
Implications of the Findings
While research generally suggests that reductions in shipping pollution have only modestly impacted temperatures, a study by James Hansen, former chief climate scientist at NASA, posits that this decline could account for nearly all of the recent temperature surge. Hausfather concludes that while the four factors together may elucidate the recent warming trends, significant questions remain.
Is this surge merely a temporary fluctuation, or does it indicate a more accelerated rate of global warming? As the world grapples with the implications of these findings, the urgency for effective climate action intensifies. The ongoing dialogue among scientists and policymakers will be crucial in addressing these pressing climate challenges.
