Four straight years of broken temperature records. A planet that just logged its first full calendar year above 1.5 degrees Celsius of warming. And now, a forecast from the United Nations’ climate science arm that says the heat is almost certainly going to intensify: there is a 91 percent chance that at least one year between 2025 and 2029 will set a new all-time global temperature record, according to the World Meteorological Organization’s latest annual-to-decadal outlook, published in June 2026.
The same forecast puts the odds at 75 percent that the five-year average itself will exceed 1.5 degrees Celsius above pre-industrial levels, and at 86 percent that the period will produce a single year warmer than any previously recorded. Those are not distant projections. They describe the world between now and the end of the decade.
Where the numbers come from
The projections originate from the WMO Lead Centre for Annual-to-Decadal Climate Prediction, operated by the UK Met Office. The centre runs a multi-model ensemble, combining outputs from several global climate models initialized with current ocean temperatures, atmospheric composition, and sea-ice conditions, then generates probabilistic forecasts using a 1991-to-2020 reference baseline.
Those forecasts do not exist in a vacuum. They build on a 2024 temperature record that four independent monitoring bodies have confirmed. NASA reported that 2024 was the warmest year since modern record-keeping began in 1880. NOAA, Berkeley Earth, and the UK Met Office Hadley Centre reached the same conclusion using separate datasets and methods. The Copernicus Climate Change Service, Europe’s independent monitoring program, added a milestone: 2024 was the first calendar year to average more than 1.5 degrees Celsius above the pre-industrial baseline. When every major temperature record agrees, the starting point for a five-year forecast is about as solid as climate science gets.
Why 1.5 degrees matters beyond a number
The 1.5-degree threshold is not arbitrary. It is the more ambitious guardrail set by the 2015 Paris Agreement, chosen because scientific assessments, including the IPCC’s 2018 special report, found that the difference between 1.5 and 2 degrees of warming translates into measurably worse outcomes: more frequent and intense heatwaves, accelerated coral reef die-offs, greater crop yield losses in tropical regions, and faster sea-level rise threatening coastal communities. Crossing 1.5 degrees in a single year does not trigger those consequences overnight, but spending more time above that line increases the cumulative damage.
The Met Office has stressed that the Paris goal is assessed over roughly 20 years of sustained temperatures, not on the basis of any single year. A calendar year averaging above 1.5 degrees does not mean the long-term threshold has been permanently breached. But the gap between a temporary spike and a sustained overshoot is narrowing. If the five-year mean also crosses 1.5 degrees, which the WMO now rates at three-in-four odds, the world moves closer to the kind of prolonged warming the Paris Agreement was designed to prevent.
What is driving the heat
Two forces dominate. The first is the long-term rise in greenhouse gas concentrations. Atmospheric carbon dioxide surpassed 420 parts per million in recent years, the highest level in at least 800,000 years, driven primarily by fossil fuel combustion. Methane concentrations have also climbed sharply over the past decade. These gases trap outgoing heat and are the primary reason global temperatures have risen roughly 1.3 degrees Celsius above pre-industrial averages on a sustained basis.
The second force is accumulated ocean heat. The oceans absorb more than 90 percent of the excess energy trapped by greenhouse gases, and ocean heat content has reached record levels in recent years. That stored energy influences surface temperatures for years afterward, which is partly why the WMO’s near-term forecast is so confident: much of the warming projected for 2025 to 2029 is already baked into the system. The residual effects of the 2023-2024 El Niño, which temporarily boosted tropical Pacific sea surface temperatures, added a short-term pulse on top of the long-term trend, though the forecast accounts for the transition back toward neutral or La Niña conditions.
What the forecast cannot tell us
The WMO outlook provides global mean probabilities but does not release regional or national anomaly maps publicly. It cannot tell a farmer in South Asia how much hotter the next monsoon season will be, or a city planner in Phoenix how many additional days above 110°F to expect. Exact model ensemble members and hindcast verification scores for the 2025-to-2029 period are not included in the public release; researchers who need that granular data must request it from the Lead Centre directly.
The forecast also does not map neatly onto specific emission scenarios. The Shared Socioeconomic Pathways used in IPCC reports project different futures depending on policy choices, but decadal forecasts like the WMO’s are initialized from observed conditions and are largely driven by climate momentum already in the system. Over a five-year window, the difference between aggressive emissions cuts and business-as-usual is relatively small compared with the warming already locked in by past emissions and ocean heat. That changes significantly over longer horizons, but for the period through 2029, the forecast reflects where the climate system is headed regardless of near-term policy shifts.
The bulletin also does not quantify how non-temperature indicators will evolve. Changes in precipitation patterns, extreme weather frequency, and compound events like simultaneous heat and drought are not captured in the headline probabilities. That leaves policymakers with a clear picture of the global temperature trajectory but less guidance on how impacts will land locally, which is often the information most needed for adaptation planning.
What the convergence of evidence means
The strength of the WMO forecast lies not in any single number but in how many independent lines of evidence point the same way. Four agencies using different methodologies confirmed that 2024 shattered the record. The WMO’s own forecasting centre, drawing on a multi-model ensemble rather than a single simulation, then projected a 91 percent chance of another breach. Wire reporting from outlets like the Associated Press has synthesized these findings, but the underlying statistics trace directly to the Met Office and WMO. Hindcast tests, in which models are run on past decades to check how well they would have predicted known outcomes, show that these ensembles reliably capture the direction and approximate magnitude of near-term warming, even when they miss individual monthly anomalies.
None of this means the Paris Agreement has formally failed. That judgment will rest on longer-term averages and on how quickly emissions fall through the 2030s and beyond. But the WMO forecast makes one thing difficult to dispute: years above 1.5 degrees Celsius are no longer outliers. The odds now favor at least one such year before the decade is out, and there is a substantial chance the five-year average will cross the same line. The threshold that once felt like a distant warning is now a level the world is repeatedly, and with increasing frequency, expected to cross.
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*This article was researched with the help of AI, with human editors creating the final content.
