Why 2025 Ranks as One of the Hottest Years in Human History Revealed – All You Must Know

In a year defined by relentless environmental challenges, 2025 is on course to go down in climate history as either the second or third warmest year ever recorded. This stark projection highlights a decade-long surge in global temperatures driven by both human-induced factors and natural variability.

As world leaders convene for the United Nations Climate Change Conference (COP30) in Belém, Brazil, the latest data underscores the urgency of reducing emissions and strengthening climate resilience.

Drawing from the World Meteorological Organization’s (WMO) State of the Global Climate Update 2025, released on 6 November 2025, this report examines the key drivers behind 2025’s exceptional heat, spanning atmospheric, oceanic, and cryospheric systems that are intensifying the planet’s warming.

Rising Greenhouse Gases: The Core Driver of 2025’s Record Heat

At the core of 2025’s record temperatures lies the relentless rise in greenhouse gas concentrations, the unseen forces fuelling global warming. Carbon dioxide (CO₂), methane, and nitrous oxide, the main contributors, reached record highs in 2024, with preliminary 2025 data showing even sharper increases.

CO₂ levels, for instance, have soared from around 278 parts per million (ppm) in the pre-industrial era to 423.9 ppm last year, marking a 53% rise. The annual increase between 2023 and 2024 alone was 3.5 ppm, the largest in decades.

These gases act like a thickening blanket, trapping heat in the atmosphere. Without substantial reductions in fossil fuel use, deforestation, and industrial emissions, the warming trend will intensify, making 2025 not an exception but a warning.

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Earth’s Expanding Heat Reservoir

The oceans, which absorb over 90% of excess heat from global warming, have also reached unprecedented levels of energy retention. Data for 2025 show a sharp rise in oceanic heat content, surpassing even the records set in 2024. This accumulation fuels more intense tropical storms, damages coral reefs, and weakens the oceans’ capacity to store carbon.

Despite transitioning from the El Niño-driven heat of 2023 and 2024 to neutral and La Niña conditions, global temperatures remained extremely high. Between January and August, the global mean surface temperature stood at 1.42°C above pre-industrial averages, slightly below 2024’s 1.55°C, yet part of a persistent warming streak. From June 2023 to August 2025, nearly every month broke heat records, with only February offering temporary relief.

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Melting Ice and the Feedback Loop of Warming

The cryosphere, Earth’s frozen zones, paints an equally troubling picture. Arctic sea ice reached its winter maximum in March at just 13.8 million square kilometres, the smallest extent since satellite records began in 1979. By September, summer ice had shrunk to 4.6 million square kilometres, well below the long-term average.

In the Antarctic, sea ice extents were the third-lowest on record, with February and September marking extreme lows and highs respectively. These losses expose darker ocean surfaces that absorb more sunlight, intensifying warming in a dangerous feedback loop.

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Meanwhile, glaciers worldwide suffered their third consecutive year of mass loss during 2023 and 2024, with the World Glacier Monitoring Service reporting a net balance of -1.3 metres water equivalent, equal to 450 gigatons of ice melted, enough to raise global sea levels by 1.2 millimetres. The rate of sea-level rise has doubled from 2.1 mm per year in the 1990s to 4.1 mm per year by 2025.

Extreme Weather: When Heat Turns Deadly

Extreme weather events provided visible proof of the planet’s distress. From floods in Africa and Asia to wildfires in Europe and North America, and heatwaves scorching cities worldwide, these disasters brought immense human and economic losses. Droughts disrupted food systems, while tropical cyclones destroyed infrastructure and livelihoods.

According to the WMO, such events were directly amplified by the same warming forces driving record temperatures.

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“This unprecedented streak of high temperatures makes it clear that it will be virtually impossible to limit global warming to 1.5°C in the next few years without temporarily overshooting this target,” warned WMO Secretary-General Celeste Saulo. She, however, maintained optimism: “It is still entirely possible and essential to bring temperatures back down to 1.5°C by the end of the century.”

Global Leaders Respond: The Call from Belém

At the Belém Climate Summit, UN Secretary-General António Guterres echoed this urgency, warning that “each year above 1.5 degrees will hammer economies, deepen inequalities, and inflict irreversible damage.”

The past eleven (11) years, from 2015 to 2025, now rank as the eleven hottest years since records began 176 years ago, with the last three being the hottest trio. The decline in aerosols, tiny particles that previously masked some warming, and the end of the multi-year La Niña phase (2020 to 2023) have further exposed the true extent of warming.

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Glimmers of Progress Amid the Crisis

Despite the alarming data, there are signs of progress. The deployment of multi-hazard early warning systems has doubled since 2015, reaching 119 countries by 2024, though about 40% remain underserved.

National meteorological services are increasingly providing climate intelligence to key sectors such as agriculture and energy, with nearly two-thirds now offering advanced tools, up from just 35% five years earlier.

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In the renewable energy sector, climate data is proving vital for managing variability in solar and wind generation, especially as 2024’s heat drove global energy demand 4% above baseline levels, with some African nations recording 30% surges.

Looking Ahead

As 2025 draws to a close, its status as one of the hottest years on record calls for reflection and decisive action. The WMO’s findings, compiled from six international datasets and the work of global experts, anchor COP30’s discussions in hard science.

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While the full 2025 report is due in March 2026, these early findings sound a clear warning: the window for a liveable planet is rapidly closing. Yet, by cutting emissions, protecting ecosystems, and strengthening adaptation measures, humanity still holds the power to reverse course.