In June 2025, the World Meteorological Organization released its annual Global Decadal Climate Update with a stark projection: the five-year stretch from 2025 through 2029 will almost certainly produce a year hotter than 2024, which already stands as the warmest in recorded history. The WMO puts the odds at 91 percent that at least one of those years will break the record, and at 75 percent that the entire five-year average will exceed 1.5 degrees Celsius above pre-industrial levels.
That 1.5-degree line is not arbitrary. It is the more ambitious target governments set in the 2015 Paris Agreement, a threshold scientists have linked to accelerating coral reef die-offs, irreversible ice sheet loss in Greenland and West Antarctica, and a sharp increase in deadly heat exposure across South Asia, the Sahel, and the Gulf states. Crossing it for a single year, as happened in 2024, does not permanently breach the Paris goal, which refers to long-term averages. But the WMO’s new numbers suggest the world is on the verge of crossing it as a sustained condition, not just a spike.
The record that set the baseline
The Copernicus Climate Change Service, operated by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission, confirmed in January 2025 that 2024 was the first full calendar year to exceed 1.5 degrees Celsius above the pre-industrial baseline. NASA’s Goddard Institute for Space Studies, NOAA’s National Centers for Environmental Information, the UK Met Office, and Berkeley Earth all independently reached the same conclusion. That level of multi-dataset agreement is unusual and leaves essentially no room for dispute about the starting point.
Copernicus’s annual climate highlights for 2024 detail the methodology: the service combines weather station readings, ocean buoy measurements, satellite observations, and atmospheric reanalysis to produce a global temperature estimate. When the WMO builds its ensemble forecasts, it calibrates against exactly this kind of verified observational record.
What the WMO forecast actually says
The WMO’s probabilistic outlook, reported by the Associated Press, reflects the combined effect of two forces that are already locked in. The first is the concentration of greenhouse gases in the atmosphere, which reached record levels in 2024 and continues to climb. The second is the enormous quantity of heat stored in the world’s oceans, which acts as a slow-release thermal battery, pushing surface temperatures higher even if emissions were to plateau tomorrow.
The 91 percent figure means that in roughly nine out of ten modeled scenarios, at least one year before 2030 will be hotter than 2024. The remaining one-in-ten scenarios where the record holds typically involve a major volcanic eruption injecting sulfur into the stratosphere or an unusually persistent La Niña phase cooling the tropical Pacific. Both are plausible but unpredictable.
The 75 percent probability that the five-year mean itself exceeds 1.5 degrees Celsius is arguably the more consequential number. A single record-breaking year can be attributed partly to natural variability, particularly El Niño. A five-year average above 1.5 degrees signals that the underlying forced warming trend has reached that level, with natural fluctuations adding to it rather than explaining it.
What the forecast does not resolve
Several important questions remain open. The WMO has not publicly released the specific ensemble model runs, baseline emissions scenarios, or confidence intervals behind its headline probabilities. That limits independent verification of the modeling assumptions for now, though the organization’s track record on multi-year forecasts has been strong: its 2020 projection that one of the following five years would temporarily hit 1.5 degrees Celsius proved correct ahead of schedule.
One factor that could make the forecast conservative is the reduction in sulfur aerosol pollution. The International Maritime Organization’s 2020 sulfur cap on shipping fuel, combined with coal plant retirements in parts of Asia and Europe, has cut emissions of sulfur dioxide, a pollutant that paradoxically exerts a short-term cooling effect by reflecting sunlight. Some researchers, including a team at NASA Goddard led by atmospheric scientist Tianle Yuan, have explored whether removing that cooling mask is accelerating surface warming faster than standard models predict. If the WMO’s projections rely on older aerosol inventories, the real probability of beating 2024 could be higher than 91 percent. Without access to the underlying model documentation, that hypothesis cannot be confirmed from the evidence at hand.
The forecast also lacks regional granularity. Global average temperature is a useful summary, but it obscures enormous variation. The Arctic is warming roughly two to four times faster than the global mean, according to research published in Communications Earth & Environment. Parts of the Southern Ocean, meanwhile, absorb heat in ways that delay local atmospheric warming. A city planner in Phoenix, a rice farmer in the Mekong Delta, and a public health official in Lagos all need localized projections, not just a single global number.
And there is the question of what happens after 2029. A 75 percent chance that the period averages above 1.5 degrees does not tell us whether temperatures stabilize, keep climbing, or temporarily dip. That trajectory depends heavily on emissions decisions governments and industries make between now and the end of the decade, decisions that remain politically contested and, in some major emitting countries, actively stalled.
What 1.5 degrees looks like on the ground
For people outside the world of climate statistics, the practical meaning of these numbers is already visible. In 2024, heat waves killed more than 60,000 people across Europe for the second time in three years, according to estimates from the Barcelona Institute for Global Health. India recorded its longest-ever heat wave, stretching across parts of Rajasthan and Uttar Pradesh for weeks. Wildfires in Canada and the western United States burned through communities that had never previously faced fire risk at that scale.
A world where the five-year average hovers at or above 1.5 degrees means those conditions become less exceptional and more routine. Energy grids face mounting demand for air conditioning during longer, more intense summers, while aging infrastructure in many regions already buckles during peak heat. The U.S. Energy Information Administration reported that residential electricity expenditures hit record highs in 2024, driven largely by cooling demand.
Agriculture faces compounding stress. Crops bred for historical temperature and rainfall patterns are increasingly exposed to heat stress and drought, even as extreme rainfall events grow more intense and can destroy yields in a single storm. The U.N. Food and Agriculture Organization flagged cereal production shortfalls in East Africa and Central America in 2024 tied directly to climate-driven weather extremes.
Public health systems are on the front line. Higher baseline temperatures raise the risk of heat-related illness and death, particularly in cities where concrete and asphalt trap heat overnight, a phenomenon known as the urban heat island effect. Planning for cooling centers, early warning systems, and targeted outreach to elderly and outdoor-working populations is shifting from emergency response to a permanent function of local government.
What makes sense now
The remaining scientific uncertainties do not weaken the case for preparation; they shape what kind of preparation makes sense. Because the observational record is firm and the forecast probabilities are high, investments that reduce vulnerability to heat, drought, and extreme rainfall qualify as low-regret moves. They pay off under almost any climate scenario consistent with current trends.
At the same time, the absence of detailed regional projections in the WMO summary underscores the need for local and national institutions to work with more granular climate data. Downscaled climate models, historical weather records, and sector-specific impact studies can translate a 1.5-degree global average into concrete expectations for river flows, crop calendars, building codes, and emergency planning in specific places.
The picture that emerges from the verified data and the WMO forecast is not one of sudden catastrophe on a fixed date. It is a steadily tightening climate envelope. The world has already lived through a full year above the 1.5-degree benchmark that once defined an ambitious limit. There is now a strong chance that the coming five years will cement that level of warming as the new background state. How disruptive that becomes depends less on the precise decimal place of global temperature and more on how quickly societies adapt and how decisively they cut the emissions driving the trend.
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*This article was researched with the help of AI, with human editors creating the final content.
