By Lina Irawan 
This stark discrepancy between expected cooling trends and the observed scorching reality raises critical questions for scientists and policymakers alike: What underlying mechanisms fueled this unexpected warmth? And what do these revelations portend for the climate outlook of 2026 and beyond?
As an Earth and environmental scientist, I dedicate my research to deciphering the myriad influences that shape global temperatures year to year. These factors range from well-understood natural phenomena like the El Niño-Southern Oscillation (ENSO) and the solar cycle, to human-induced impacts such as vast wildfires and, crucially, the complex dynamics of atmospheric aerosols. Some of these influences naturally push Earth’s temperature higher, while others exert a cooling effect. What has become increasingly clear, however, is that one particularly detrimental influence, sulfate aerosol pollution, had been quietly masking a substantial amount of human-caused global warming – a protective veil that has now thinned considerably, revealing the true, accelerated pace of planetary heating.
The data for the past three years paints a stark picture of unprecedented warmth. The chart compiled by the European Union’s Copernicus Climate Change Service vividly illustrates this trajectory, comparing current temperatures to those of the preindustrial era in the latter half of the 1800s. The upward trend is undeniable, underscoring the urgency of understanding the complex interplay of factors driving this warming.
Factors That Should Have Cooled 2025 (But Didn’t Enough)
The Earth’s climate system is a delicate balance of numerous interacting components, many of which fluctuate annually. In 2025, several factors were anticipated to exert a cooling influence, suggesting that the year should have been notably cooler than its immediate predecessor, 2024. The fact that it wasn’t highlights the overriding power of other warming forces.
La Niña’s Arrival: A Brief Respite that Wasn’t Enough
Central to Earth’s interannual climate variability is the El Niño-Southern Oscillation (ENSO), a natural climate pattern characterized by fluctuating sea surface temperatures in the equatorial Pacific Ocean. ENSO cycles through three phases: El Niño (warm), La Niña (cool), and neutral. During an El Niño event, the central and eastern equatorial Pacific warms significantly, releasing vast amounts of heat into the atmosphere. This warming disrupts atmospheric circulation patterns globally, leading to more intense storms, prolonged droughts, and widespread heat waves in various regions. Conversely, La Niña is characterized by cooler-than-average sea surface temperatures in the same region, acting much like a massive "ice pack" on the atmosphere. This cooling effect typically dampens global temperatures.
Both 2023 and 2024 were profoundly influenced by a powerful El Niño, contributing significantly to their record-breaking warmth. Expectations for 2025 were that conditions would shift, moving from El Niño to neutral, and then transitioning into a La Niña phase starting in September. This expected shift was a primary reason scientists anticipated a cooler 2025. While La Niña did indeed emerge, its cooling impact was evidently insufficient to significantly counteract the underlying warming trends.
The Solar Cycle: A Diminishing but Minor Influence
Another natural modulator of Earth’s climate is the Sun’s approximately 11-year solar cycle, which sees variations in its energy output. The Sun reached its solar maximum—the peak of its energy emission—near the end of 2024. Consequently, in 2025, the Sun’s output began its slow decline towards a solar minimum. While the Sun’s energy output in 2025 was still stronger than its average over the full cycle, it was measurably less than the peak observed in 2024. This reduction in solar irradiance, though small, should theoretically have contributed to a slight global cooling effect. However, compared to the overwhelming anthropogenic influences, its impact on the overall temperature anomaly for 2025 was minimal.
Fewer Wildfires: A Localized Improvement, Global Challenge
Wildfires, particularly large-scale events, are significant contributors to atmospheric carbon dioxide – a potent planet-warming greenhouse gas – and also release aerosols that can have short-term regional cooling or warming effects. While 2025 still witnessed destructive blazes in various parts of the world, global data indicated a reduction in the overall extent and intensity of wildfires compared to the exceptionally severe fire season of 2024. For instance, the Canadian wildfires of 2023, which continued into 2024, released unprecedented amounts of carbon into the atmosphere. A less active global wildfire season in 2025 should have theoretically meant less carbon dioxide emissions from this source, contributing to a slightly cooler atmospheric burden. However, much like the other cooling factors, the reduced wildfire emissions were not enough to offset the persistent and growing warming drivers.
Despite the combined potential cooling influences from the nascent La Niña, the declining solar cycle, and fewer wildfires, 2025 stubbornly registered as the third-hottest year in over 175 years of meticulous record-keeping. Furthermore, analyses suggest it was likely one of the warmest years in at least several thousand years, placing it in an extraordinary historical context. According to the European Union’s Copernicus Climate Change Service, 2025 was nearly as warm as the record-breaking 2023, averaging a staggering 2.6 degrees Fahrenheit (1.47 Celsius) above the 1850-1900 preindustrial average. The land surface experienced even more pronounced warming, with the second-highest average land temperature recorded, up 3.6 F (2 C) compared to preindustrial levels. Disturbingly, over 10% of the Earth’s land area experienced record-high temperatures, a clear indicator of widespread and intense heat.
Factors That Made 2025 Warmer Than Expected
The persistent warmth of 2025, defying several expected cooling influences, points to powerful and escalating warming factors, many of which are projected to intensify into 2026.
Unabated Greenhouse Gas Emissions: The Overriding Driver
The single most significant and enduring driver of global warming remains the relentless accumulation of excess greenhouse gas emissions, predominantly from the combustion of fossil fuels (coal, oil, and natural gas). These gases – primarily carbon dioxide, methane, and nitrous oxide – act like an insulating blanket, trapping heat near Earth’s surface that would otherwise radiate back into space, thereby raising global temperatures. A critical characteristic of these gases is their long atmospheric residence time; emissions released today will continue to warm the planet for years, decades, or even centuries to come. In 2025, monitoring stations worldwide, such as those operated by NOAA, confirmed continued increases in the atmospheric concentrations of carbon dioxide, methane, and nitrous oxide, reaching unprecedented levels.
The global energy landscape in 2025 saw rising energy demand fueling an increase in fossil fuel consumption. Approximately 80% of this escalating demand for electric power originated from emerging economies, driven in large part by the increasing need for air conditioning as global temperatures rise. In more developed nations, the rapid expansion of energy-intensive sectors, such as data centers supporting artificial intelligence (AI) and cryptocurrency mining, contributed significantly. For instance, in the U.S., these sectors helped boost carbon dioxide emissions by an estimated 2.4%. This highlights a critical challenge: while renewable energy deployment is accelerating, it is not yet keeping pace with the overall increase in global energy demand, leading to a continued reliance on carbon-intensive sources.
Earth’s Energy Imbalance: A Planet Out of Sync
Beyond direct greenhouse gas emissions, other factors can disrupt Earth’s delicate energy balance – the equilibrium between incoming solar radiation and outgoing thermal radiation. A recent study shed light on how this balance can dramatically shift, noting a significant surge in Earth’s energy uptake and rapid temperature increases when the rare three-year La Niña event from 2020-2022 transitioned into the powerful El Niño of 2023-2024. This rapid shift released previously stored ocean heat into the atmosphere, contributing to the exceptional warmth observed.
Declining Polar Ice and the Albedo Effect:
Another crucial element in Earth’s energy balance is the extent of polar ice. Ice and snow are highly reflective, possessing a high albedo, meaning they efficiently reflect sunlight back into space, thus helping to cool the planet. As sea ice melts, it exposes darker ocean water beneath, which absorbs most of the sunlight that reaches it. This creates a dangerous positive feedback loop: warmer water melts more sea ice, which in turn allows the ocean to absorb even more sunlight, accelerating warming. In 2025, this feedback loop was painfully evident: the Arctic experienced its lowest winter peak of sea ice on record, while the Antarctic saw its third-lowest minimum extent of ice. These record lows mean less reflective surface and more heat absorption, contributing directly to the observed global temperature rise.
The "Dirty Surprise": The Unmasking Effect of Reduced Air Pollution
Perhaps one of the most significant, yet often overlooked, factors contributing to 2025’s unexpected warmth is the reduction in sulfate aerosol pollution. For decades, sulfate aerosols, primarily emitted from the combustion of coal and heavy fuel oil in industrial processes and shipping, have exerted a significant cooling effect on the planet. These tiny airborne particles reflect incoming sunlight back into space, effectively masking a portion of the warming caused by human-induced greenhouse gases. However, while offering a temporary "cooling" reprieve, sulfate aerosols are also a severe public health hazard, directly linked to approximately 8 million human deaths annually from respiratory and cardiovascular diseases.
Recent global efforts to improve air quality have led to substantial reductions in sulfate pollution. Globally, sulfate aerosols are now about 40% less abundant than they were 20 years ago. Much of this reduction stems from China’s concerted efforts to combat its notoriously severe air pollution in recent years, as well as stringent international shipping regulations implemented since 2020, which have reduced sulfur emissions from large vessels by an impressive 85%. While these pollution reductions are a resounding success for public health and local air quality, they have an unintended consequence for global temperatures. Scientists estimate that this reduction in the reflective aerosol shield has contributed to an approximate 0.2 F (0.13 C) increase in global temperatures, effectively unmasking a portion of the greenhouse gas warming that had previously been hidden. This reveals that the true warming effect of greenhouse gases is even more pronounced than what we have directly observed for decades.
An Accelerated Pace of Warming and Its Consequences
When all these factors are considered in concert, the inescapable conclusion is that humanity is now warming the planet at an unprecedented rate – approximately 0.5 F (0.27 C) per decade. This accelerated influx of heat into the Earth’s climate system has profound and immediate consequences, directly fueling the increase in extreme weather events witnessed globally. Flash floods become more intense as a warmer atmosphere holds more moisture. Heat waves become more frequent, longer-lasting, and more severe. Extended droughts deepen, exacerbating water scarcity and agricultural failures. Wildfires rage with greater intensity and over larger areas, and coastal flooding becomes more commonplace and damaging as sea levels rise and storm surges intensify. These events inflict immense human suffering, disrupt ecosystems, and incur staggering economic costs.
Predictions for 2026: A Future Shaped by Current Actions
Looking ahead, most climate models predict that 2026 will be approximately as hot as 2025, a sobering forecast given the previous year’s exceptional warmth. The precise trajectory for 2026 will heavily depend on the evolution of the Pacific ENSO cycle, with forecasters currently giving about a 60% chance of an El Niño developing. Should another El Niño emerge, its warming influence could counteract any lingering cooling from the current La Niña. The year is already off to a warm start; while January brought severe cold to parts of the U.S., globally, Earth experienced its fifth-warmest January on record. Moreover, much of the western U.S. recorded one of its warmest winters on record, underscoring the regional variability but persistent global trend of rising temperatures.
While the Sun’s output will continue its slow, minor decrease in 2026, its cooling effect will be negligible compared to anthropogenic forces. The International Monetary Fund projects robust global economic growth of about 3.3% for 2026. This economic expansion, while desirable in many respects, directly translates to increased energy demand. The International Energy Agency anticipates that global electricity demand will continue to surge by an average of 3.6% per year through at least 2030.
Crucially, even with significant and accelerating investments in renewable energy, its growth is currently not fast enough to meet this burgeoning demand. This unfortunate reality means that fossil fuels will continue to play a substantial role in the global energy mix in the coming years. More fossil fuels burned translate directly to more greenhouse gas emissions and, consequently, more global warming. Compounding this challenge is the diminishing capacity of natural carbon sinks – the oceans and land ecosystems – to absorb atmospheric carbon dioxide, meaning a greater proportion of emissions remains in the atmosphere, accelerating warming.
As the atmosphere and oceans continue to heat up, the risks of crossing critical climate tipping points increase dramatically. These are thresholds beyond which significant and irreversible changes to Earth’s climate system become inevitable. Examples include the irreversible disappearance of major glaciers, the potential shutdown of the Atlantic Ocean circulation system (AMOC), widespread thawing of permafrost releasing vast stores of methane, and the catastrophic die-off of coral reefs.
In conclusion, the exceptional warmth of 2025, despite factors that should have led to a cooler year, serves as a stark warning. It underscores the profound impact of unabated greenhouse gas emissions and highlights the complex, and sometimes counterintuitive, ways in which human activities are reshaping our planet. If current rates of greenhouse gas emissions continue, humanity may very well look back at 2025 as one of the coolest years globally in the remainder of our lives, facing a future defined by ever-increasing temperatures and more frequent, severe climate extremes.
Michael Wysession, Professor of Earth, Environmental, and Planetary Sciences, Washington University in St. Louis
This article is republished from The Conversation under a Creative Commons license. Read the original article.