Executive Summary
The WMO’s State of the Global Climate 2025 shows that 2025 was slightly cooler than 2024 at the surface, but it was not a cooler climate year. Global temperature remained 1.43°C above the 1850–1900 baseline, ranking second or third on record. Meanwhile, greenhouse gases continued to rise, ocean heat content set another record, sea level stayed near record highs, and Earth’s energy imbalance reached its highest observed level. The climate system continued to accumulate heat even as short-term variability muted surface signals.
Earth’s Energy Imbalance Emerges as the Defining Signal
The report’s most significant update is Earth’s energy imbalance, which measures the difference between incoming and outgoing energy. In 2025, it reached its highest point in the observational record, confirming that the planet continues to gain heat overall. This is important because about 91% of the excess heat is stored in the ocean, not the atmosphere, so surface air temperature alone only tells part of the warming story.
2025 Remained One of the Hottest Years on Record
Using standard temperature measures, 2025 remained remarkable. WMO’s nine-dataset synthesis shows it at 1.43°C above the pre-industrial baseline, with only 2024 being clearly warmer. The years 2015–2025 rank as the 11 warmest on record, and 2023–2025 ranks as the warmest three-year period across all datasets. The transition from El Niño to neutral and weak La Niña conditions explains some of the moderation in 2024, but it does not reverse the overall long-term trend.
Greenhouse Gas Concentrations Continued to Drive the Trend
The driving force behind the warming also continued to grow stronger. Atmospheric CO2 reached 423.9 ppm in 2024, while methane and nitrous oxide remained at very high levels. About half of human CO2 emissions still stay in the atmosphere, and the recent sharp increase reflects not only ongoing fossil fuel burning but also fires and weaker natural carbon sinks. In other words, the fundamental greenhouse baseline did not pause.
Oceans, Ice, and Sea Level Show Persistent System Change
The ocean and cryosphere show clear signs of ongoing, system-wide change. Ocean heat content in the top 2,000 meters reached another record in 2025, and around 90% of the ocean surface experienced at least one marine heatwave. Global average sea level remained near record highs, about 11 cm above its 1993 level, with the rate of increase accelerating. Ocean acidification persisted, glaciers remained near historic mass-loss extremes, and Arctic and Antarctic sea ice stayed significantly below the 1991–2020 average.
Climate Impacts Are Intensifying Faster Than Preparedness
These physical changes are already increasing the risk. The report highlights increasingly uneven rainfall, destructive floods, wildfires, cyclone damage, an expanding dengue risk, and rising workplace heat stress. It also notes that preparedness still lags, with only about half of countries providing heat early warning services tailored to health needs. WMO is careful to point out that a single year above 1.5°C does not officially violate the Paris threshold, which is assessed over decades, but the overall conclusion remains the same: 2025 was not a year of relief, only a slightly less extreme year within an ongoing warming trend.
Frequently Asked Questions (FAQs)
- Why does a slightly cooler year not mean climate change is slowing down? Because 2025 was only slightly cooler than 2024 at the surface, while the broader climate system continued to accumulate heat. Ocean heat content, sea level, and Earth’s energy imbalance all remained extremely high, showing that the long-term warming trend is still intact.
- What is Earth’s energy imbalance, and why does it matter? Earth’s energy imbalance measures the difference between the energy the planet receives from the sun and the energy it sends back into space. As that imbalance grows, the planet as a whole heats up, making it one of the clearest indicators that global warming is continuing.
- Why is the ocean so important in understanding global warming? The ocean absorbs about 91% of the excess heat trapped by greenhouse gases. That means air temperature alone does not capture the full picture, because much of the warming is being stored in the ocean and contributing to marine heatwaves, sea level rise, and long-term system change.
- Did 2025 exceed the Paris Agreement’s 1.5°C limit? A single year above 1.5°C does not officially mean the Paris threshold has been breached. The Paris benchmark is assessed over longer, multi-decade periods rather than a single year.
- What were the clearest warning signs in 2025 besides air temperature? The strongest warning signs included record ocean heat content, widespread marine heatwaves, accelerating sea level rise, continued ocean acidification, major glacier mass loss, and persistently low Arctic and Antarctic sea ice. Together, these show that climate risk is deepening across the whole Earth system.
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