In June 2024, New Delhi hit 52.9 degrees Celsius (127.2°F), a temperature so extreme that roads buckled and hospitals ran out of beds for heatstroke patients. Months later, NASA and the European Union’s Copernicus Climate Change Service independently confirmed what the year’s disasters had already made obvious: 2024 was the hottest year in the modern instrumental record, and the first calendar year to exceed 1.5 degrees Celsius above pre-industrial levels. Now, as of June 2026, the World Meteorological Organization is warning that 2024’s record is unlikely to stand for long. Its latest decadal forecast puts the odds that at least one year between 2025 and 2029 will be even hotter at 91 percent, with a 75 percent chance the entire five-year average will top the 1.5°C mark that 196 nations pledged to avoid under the Paris Agreement.
The baseline that makes the forecast so stark
The WMO projection rests on a foundation of observed data that has been cross-checked by two of the world’s most rigorous monitoring systems. NASA‘s Goddard Institute for Space Studies builds its GISTEMP record from tens of thousands of weather stations, ship-based ocean readings, and Antarctic research outposts stretching back to 1880. Copernicus takes a different route, blending satellite observations, weather-balloon soundings, and surface measurements into a global reanalysis (ERA5) that uses atmospheric modeling to fill gaps over oceans and polar regions. When both systems independently land on the same conclusion, the finding carries unusual institutional weight.
Their shared conclusion for 2024 was blunt: the planet’s average surface temperature ran roughly 1.55°C above the 1850-1900 baseline. That figure nudged past the previous record, set just one year earlier in 2023, by a margin large enough to sit well outside the range of measurement uncertainty. Copernicus director Carlo Buontempo called the crossing of 1.5°C for a full calendar year “more than a statistical milestone” when the data were published.
A single year above 1.5°C does not constitute a permanent breach of the Paris target, which is defined as a multi-decade average. But it reveals how thin the buffer has become. The WMO outlook suggests that buffer is about to shrink further.
Why the oceans are the key variable
Sea-surface temperatures played an outsized role in pushing 2024 past previous records. The El Niño event that peaked in late 2023 and early 2024 redistributed vast stores of ocean heat into the atmosphere, temporarily inflating global averages. That much was expected. What surprised researchers was that ocean temperatures stayed elevated even after the tropical Pacific shifted toward neutral conditions in mid-2024.
Because the oceans absorb more than 90 percent of the excess energy trapped by rising greenhouse-gas concentrations, according to the Intergovernmental Panel on Climate Change’s Sixth Assessment Report, persistent marine heat anomalies can lock in higher global averages for years. Several climate scientists, including Gavin Schmidt, director of NASA’s Goddard Institute, have publicly noted that the scale of the 2023-2024 ocean warming exceeded what standard models predicted from El Niño and greenhouse forcing alone, raising questions about whether a poorly understood additional mechanism is at work.
That unresolved question feeds directly into the uncertainty around the WMO’s five-year outlook. If the extra ocean heat proves to be a temporary anomaly, the 91 percent probability of a new record could sit at the high end of reality. If it reflects a structural shift in how the oceans store and release energy, the forecast may actually be conservative.
What the forecast does and does not tell us
Probabilistic climate forecasts like the WMO’s are built by running dozens of model simulations with slightly varied starting conditions and counting how many cross a given threshold. A 91 percent probability does not guarantee a new annual record; it means that in the vast majority of plausible scenarios the models tested, at least one year through 2029 surpasses 2024. The 75 percent figure for the five-year average clearing 1.5°C carries similar weight: a strong signal, not a certainty.
Several factors could shift the outcome. A strong La Niña phase would temporarily cool global averages, potentially delaying the next record by a year or two. A major volcanic eruption, like the 1991 Mount Pinatubo event that cooled the planet by roughly 0.5°C for two years, could do the same. Conversely, continued acceleration of fossil-fuel emissions or an abrupt slowdown in the Atlantic Meridional Overturning Circulation could push temperatures higher than the central forecast.
The WMO has not published the full ensemble model outputs or the specific emissions scenarios behind its headline numbers in the materials reviewed for this article. That limits independent verification of the modeling assumptions, though the organization’s seasonal and annual forecasts have a strong track record: its 2020 projection that one of the following five years would temporarily exceed 1.5°C proved correct ahead of schedule.
Regional breakdowns are also absent from the current forecast. Arctic amplification, shifting monsoon patterns, and accelerating ice-sheet loss are well-documented phenomena in the broader climate literature, but the WMO outlook does not specify how the projected warming will distribute across continents or ocean basins. For city planners and water managers, the forecast is a directional alarm, not a localized blueprint.
What 2024 already cost
The urgency of the WMO warning is easier to grasp against the backdrop of what record heat already did. According to the WMO’s own State of the Global Climate 2024 report, the year brought the deadliest wildfire in modern U.S. history (Maui, August 2023, with impacts extending into 2024 recovery), catastrophic flooding across East Africa, and a record Atlantic hurricane season that included Hurricane Helene, which killed more than 200 people across the southeastern United States. Global crop-insurance losses from weather extremes reached new highs, and coral-reef bleaching spread across every tropical ocean basin for only the fourth time on record.
Health systems bore a particular burden. The Lancet Countdown on Health and Climate Change reported that heat-related mortality among people over 65 reached record levels in 2024, with South Asia, the Middle East, and sub-Saharan Africa hit hardest. Emergency departments in cities from Phoenix to Karachi saw surges in heatstroke, kidney injury, and cardiovascular events during prolonged heat waves that, in several cases, broke not just temperature records but duration records.
If the WMO’s probability distribution holds, similar or worse conditions are not a mid-century scenario. They are a near-term planning horizon.
Where the margin for action stands
The distinction between a single year above 1.5°C and a long-term breach of the Paris target still matters, because it defines the remaining window for intervention. Global greenhouse-gas emissions have not yet peaked, according to the Global Carbon Project’s 2024 budget, but the rate of increase has slowed as renewable-energy deployment accelerates. The International Energy Agency reported in late 2024 that solar power alone accounted for more new electricity-generation capacity worldwide than all other sources combined for the first time.
None of that changes the physics already baked into the system. Even if emissions dropped to zero tomorrow, the heat stored in the oceans and the long atmospheric lifetime of carbon dioxide would keep temperatures elevated for decades. The WMO forecast, in that sense, is partly a reflection of choices already made.
But “partly” is the operative word. The difference between a world that holds near 1.5°C over the long term and one that drifts toward 2°C or beyond translates into hundreds of millions of people exposed to deadly heat, meters of additional sea-level rise, and the survival or collapse of ecosystems from coral reefs to boreal forests. Investments in cooling infrastructure, resilient power grids, urban tree canopy, and water storage that once seemed like mid-century preparations now look like measures needed within the current decade. The WMO’s numbers do not tell any single city what summer 2027 will feel like. They do make clear that planning for a return to “normal” is no longer a defensible strategy.
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*This article was researched with the help of AI, with human editors creating the final content.
