The planet keeps setting temperature records because the atmosphere now holds more heat-trapping gases than at any point in human history, and the effects compound over time. The ten warmest years on record have all occurred since 2015. Even in a year without a major El Niño event pushing temperatures higher, the baseline has shifted so much that “normal” now feels persistently hot.
More CO2 Means More Trapped Heat
Carbon dioxide in the atmosphere acts like a thickening blanket around the planet. As of early 2026, concentrations at the Mauna Loa observatory in Hawaii reached 430 parts per million, up from 427 ppm just one year earlier. For context, before the Industrial Revolution, that number hovered around 280 ppm. Every additional molecule of CO2 absorbs outgoing heat radiation and redirects some of it back toward Earth’s surface.
This isn’t a subtle effect. NOAA ranked 2025 as the third-warmest year in records going back to 1850, with global surface temperatures running 1.17°C above the 20th-century average. That came after 2024 set the all-time record, and 2023 claimed second place. The pattern is relentless: the atmosphere traps more energy each year, and average temperatures ratchet upward.
The Ocean Stores Heat for Decades
One reason it stays hot even when emissions discussions dominate the news is thermal inertia. The ocean absorbs roughly 90% of the excess energy trapped by greenhouse gases, and it releases that heat slowly over decades. Think of it like heating a massive pot of water on a stove: even after you turn down the burner, the water stays hot for a long time.
This creates what climate scientists call a “pipeline” of future warming. NASA research confirms that if all fossil fuel burning stopped today, the Earth would still warm further before reaching a new equilibrium. The heat already stored in the ocean guarantees additional warming over the coming decades. That lag between cause and effect is part of why temperatures remain stubbornly high even as the conversation around emissions intensifies.
The Arctic Is Warming Four Times Faster
Not every part of the planet warms at the same rate. The Arctic has heated nearly four times faster than the global average since 1979, warming at about 0.73°C per decade compared to the global rate of 0.19°C per decade. Earlier estimates often cited two or three times faster, but a study in Communications Earth & Environment showed those figures underestimated the trend.
The main driver is disappearing sea ice. Ice reflects sunlight back into space, but as it melts, the dark ocean beneath absorbs that energy instead, which melts more ice, which exposes more ocean. This feedback loop accelerates warming at the poles. It also destabilizes the jet stream, the river of fast-moving air that normally keeps cold Arctic air separated from warmer air to the south. When the jet stream weakens or wobbles, it can lock heat domes in place over populated areas for days or weeks at a time.
Heat Domes and Blocking Patterns
If you’ve noticed a stretch of relentless heat that just won’t break, you may be under a heat dome. This happens when a persistent high-pressure system parks itself over a region and acts like a lid on a pot. Air sinks within the high-pressure zone, compressing and warming as it descends. The dome blocks cooler air and storm systems from moving in, so temperatures build day after day.
Heat domes can stretch across several states and last anywhere from a few days to more than two weeks. They can also drift, baking one region before sliding over to punish a neighboring area. These events have always occurred, but a warmer atmosphere raises their ceiling. The same blocking pattern that might have produced a few 95°F days in 1990 can now deliver 105°F days because the baseline temperature is higher to begin with.
Natural Cycles Still Matter
Earth’s climate rides on top of natural oscillations that temporarily push temperatures up or down. The biggest is the El Niño-Southern Oscillation, or ENSO. During El Niño years, warm water spreads across the tropical Pacific and adds extra heat to the atmosphere. During La Niña, cooler-than-normal Pacific waters pull global temperatures down slightly. As of early 2026, the planet is in a La Niña phase, with Pacific sea surface temperatures running about 0.9°C below average in the key monitoring region.
That context makes recent temperatures even more striking. La Niña typically acts as a cooling influence, yet 2025 still ranked as the third-warmest year ever recorded. The greenhouse gas signal is now so strong that even a cooling natural cycle can’t bring temperatures back to what used to be normal.
Solar activity plays a smaller role. The sun goes through roughly 11-year cycles of higher and lower output. Solar Cycle 25 is expected to peak around mid-2025, which adds a small amount of energy to the climate system. But the sun’s contribution to year-to-year temperature swings is only a fraction of a degree, far less than the warming driven by CO2 and other greenhouse gases.
Cities Feel It More
If you live in a city, the heat you’re experiencing is amplified by the urban heat island effect. Concrete, asphalt, and steel absorb solar energy during the day and radiate it back at night, keeping urban areas warmer than surrounding countryside. In most cities, this effect is strongest after dark, which is why summer nights in urban areas can feel oppressively warm even after the sun sets.
The size of this effect varies. Research examining 54 U.S. cities found that nighttime urban heat islands are larger than daytime ones in about two-thirds of cases. During extreme heat events, the picture gets more complex. In roughly a third of cities studied, the urban-rural temperature gap actually shrank during the most intense heat waves, sometimes even flipping so that the city was slightly cooler than surrounding rural land on the hottest nights. But for everyday warm weather, cities consistently run hotter, and that extra warmth stacks on top of the broader climate trend.
Why It Won’t Cool Down Soon
The short answer is that the factors driving persistent heat operate on long timescales. CO2 lingers in the atmosphere for centuries. The ocean will continue releasing stored heat for decades. Arctic ice loss feeds on itself. Even with aggressive emissions reductions, the thermal inertia built into the system means temperatures will keep climbing for a while before they stabilize.
Methane and soot are shorter-lived warming agents, which means reducing them could slow the pace of warming more quickly than cutting CO2 alone. But the CO2 already in the atmosphere, now at 430 ppm and climbing about 3 ppm per year, ensures that the baseline stays elevated. Each year’s weather plays out on top of a warmer foundation than the year before, which is why heat that once would have been record-breaking now feels like just another summer.