1518. Annual Update of Key Climate Indicators: Accelerating Warming and Surging Marine Heatwaves Signal a New Phase

An international team of researchers has released the annual report “Indicators of Global Climate Change 2025,” which provides a comprehensive assessment of the state of the climate system and the extent of human influence. This report systematically updates key indicators of climate change—from greenhouse gas emissions to the Earth’s energy balance and climate extremes—based on methodologies consistent with the IPCC Sixth Assessment Report (AR6).

One of the most significant findings of this analysis is the rapid expansion of the Earth’s Energy Imbalance (EEI), an integrative indicator of global warming. EEI represents the difference between the energy Earth receives from the Sun and the energy it radiates back into space. In recent years, this imbalance has more than doubled compared to the 1976–1995 period, indicating a substantial increase in the amount of heat accumulating within the climate system and suggesting an acceleration of global warming.

Another notable development is the introduction of a new indicator: the number of marine heatwave days. The analysis shows a marked increase in these events, with the number of days experiencing abnormally high sea surface temperatures more than tripling between 1991 and 2025. This trend highlights rapid changes in the ocean environment. Marine heatwaves not only affect marine ecosystems but also influence atmospheric circulation and extreme weather patterns, making them a critical signal of growing climate risks.

In terms of temperature, the decade average for 2016–2025 shows a global mean surface warming of 1.26°C relative to pre-industrial levels (1850–1900), with nearly all of this warming (approximately 1.24°C) attributed to human activities. In 2025 alone, human-induced warming reached 1.37°C, bringing global temperatures closer to the 1.5°C target established under the Paris Agreement.

The rate of warming also remains elevated. Human-induced warming has increased at a rate of approximately 0.27°C per decade over the past ten years, representing the highest rate observed in the instrumental record.

Global greenhouse gas emissions continue to rise, reaching a record high of 56.8 GtCO₂e in 2024. Fossil fuel-related CO₂ emissions account for the majority of this total, while methane and nitrous oxide emissions are also increasing. However, there are emerging signs that the growth rate of emissions is slowing, suggesting that energy transitions and climate policies may be beginning to have an impact.

As a result of sustained emissions, atmospheric concentrations of greenhouse gases continue to increase, contributing to a rise in anthropogenic effective radiative forcing, which reached 3.10 W/m² in 2025 relative to pre-industrial levels. This increase in forcing, combined with a weakening of aerosol cooling, has driven further increases in the Earth’s energy imbalance. Consequently, heat uptake by the oceans has intensified, with warming penetrating into deeper ocean layers.

Sea-level rise is also accelerating. Global mean sea level has risen by approximately 23 cm between 1901 and 2025, with recent rates reaching about 3.8 mm per year. At the same time, extreme land temperatures and precipitation variability continue to intensify, indicating that multiple dimensions of climate extremes are evolving simultaneously.

Meanwhile, the remaining carbon budget for limiting warming to 1.5°C is shrinking rapidly. As of 2026, the remaining budget is estimated at approximately 130 GtCO₂ for a 50% likelihood of staying within the target. At current emission levels, this budget would be exhausted within only a few years, suggesting that global warming could reach 1.5°C around 2030.

The report also raises serious concerns about the vulnerability of the global climate observation system itself. Reductions in satellite missions, ocean monitoring programs, and atmospheric observations, along with declining funding for international coordination bodies, pose risks to our ability to continuously monitor the climate system. Maintaining these observation networks is critical for both scientific understanding and evidence-based policymaking.

Overall, this annual update demonstrates that climate change is no longer characterized solely by gradual temperature increases. Instead, multiple components of the climate system—including energy balance, oceans, and extreme events—are changing simultaneously, with increasing intensity. In particular, the rapid rise in marine heatwaves and the expansion of the Earth’s energy imbalance suggest that the climate system may be entering a new phase. The trajectory of future emissions reductions will therefore play a decisive role in shaping climate outcomes in the coming decades.

Reference:

Forster, P. M. et al. (2026). Indicators of Global Climate Change 2025: annual update of key indicators of the state of the climate system and human influence. Earth System Science Data.

https://essd.copernicus.org/articles/18/3889/2026/

Contributor: Miyuki IIYAMA, Strategic Coordination Office