The planet is in the middle of its hottest stretch in recorded history. 2024 was the warmest year since records began in 1850, followed closely by 2023 in second place and 2025 in third. All ten of the warmest years on record have occurred since 2015. The heat you’re feeling isn’t just a local fluke or a bad summer. It’s the result of several forces, some long-term and some short-term, stacking on top of each other at the same time.
The Baseline Keeps Rising
The single biggest reason it’s hotter now than in previous decades is the steady accumulation of heat-trapping gases in the atmosphere. Carbon dioxide and methane act like a thickening blanket around the planet, letting sunlight in but slowing the escape of heat back into space. Methane concentrations reached about 1,947 parts per billion in late 2025, climbing nearly 7 parts per billion in 2024 alone. Each year adds more insulation, and the warming compounds over time.
This long-term trend means that every weather pattern, every heat wave, and every warm season now starts from a higher baseline temperature than it would have a few decades ago. In 2025, the global surface temperature was 1.34°C above the pre-industrial average. That might sound small, but it represents an enormous amount of extra energy stored across the entire planet’s surface, oceans, and atmosphere.
Record-Breaking Ocean Temperatures
Oceans absorb the vast majority of the extra heat trapped by greenhouse gases, and they’ve been running a fever. North Atlantic sea surface temperatures in 2023 and 2024 shattered the previous record by 0.42°C, a margin that was actually larger than the global record-breaking margin during the same period. Warmer oceans don’t just affect marine life. They pump more heat and moisture into the atmosphere, fueling hotter conditions on land and making heat waves more intense and longer-lasting.
Ocean temperatures also influence large-scale climate cycles. The Pacific’s El Niño-Southern Oscillation (ENSO) pattern swung through an El Niño phase in 2023 and into early 2024, which redistributes warm water across the tropical Pacific and temporarily boosts global temperatures. That was followed by a brief La Niña in late 2024 (which typically has a cooling effect), but by spring 2025 the tropical Pacific had returned to neutral. Forecasters expect neutral conditions to persist through summer 2025, with La Niña roughly twice as likely as El Niño later in the year. Even without El Niño’s extra push, global temperatures have remained remarkably high.
Cleaner Shipping Fuel, Less Cooling Pollution
One factor that has surprised even climate scientists is the role of cleaner air. In 2020, international maritime regulations sharply reduced the sulfur content in shipping fuel. Sulfur particles from ship exhaust had been reflecting a small amount of sunlight back into space, creating a slight cooling effect over the oceans, particularly along busy shipping lanes. Removing that pollution was good for air quality and human health, but it also removed a thin shield against solar heating.
The effect is measurable: the regulation added roughly 0.05°C to global average temperatures in the 2020s, equivalent to about two to three years’ worth of additional warming arriving all at once. That’s a small number globally, but it helps explain why the temperature jump in 2023 and 2024 was so sharp and why ocean warming in the North Atlantic was so dramatic.
Heat Domes and Stuck Weather Patterns
If you’re asking “why is it so hot right now” rather than “why is it hotter than it used to be,” the answer often involves heat domes. A heat dome forms when a persistent high-pressure system parks itself over a region, trapping hot air underneath. The high pressure forces air downward, compressing and heating it further. Clouds can’t form easily under these conditions, so the sun bakes the ground day after day with little relief.
Heat domes are linked to the behavior of the jet stream, the river of fast-moving air high in the atmosphere that steers weather systems across the mid-latitudes. Normally, the jet stream keeps weather moving along. But research from Columbia University’s Lamont-Doherty Earth Observatory has found that climate change is making the jet stream “lazier,” with bigger, slower-moving waves. When these waves grow and stall, they create blocked weather patterns where high-pressure ridges sit in place for days or even weeks. The result is longer, more intense heat waves.
Declining spring snow cover in North America is one factor driving this change. Less snow means the ground absorbs more solar energy earlier in the season, altering temperature contrasts that influence the jet stream’s path. Air descending down mountain slopes can intensify the effect further, warming as it drops in elevation.
The Sun Isn’t the Main Driver
Solar activity follows an approximately 11-year cycle, and Solar Cycle 25 reached its peak recently. It’s reasonable to wonder whether a more active sun explains the heat. The short answer: it contributes very little. During even strong solar cycles, the sun’s brightness varies by a small enough amount that it shifts global temperatures by 0.1°C or less. Over the entire industrial period, the sun’s changing output has contributed an estimated 0.01°C of warming, a tiny fraction of the roughly 1.3°C increase observed so far.
In fact, solar activity in recent cycles has been among the lowest in a century. The increases and decreases in solar output over the past hundred years have largely canceled each other out. The heat you’re experiencing is overwhelmingly driven by greenhouse gases and the amplifying factors described above, not by a hotter sun.
Why the Heat Feels Worse Than the Numbers Suggest
Temperature readings alone don’t capture how dangerous heat can be. Your body cools itself by sweating, and sweat only works when the surrounding air is dry enough for it to evaporate. Scientists measure this using wet-bulb temperature, which accounts for both heat and humidity. A wet-bulb temperature of 35°C (95°F) was long considered the theoretical upper limit of human survivability, the point where even a healthy person sitting in the shade could develop fatal overheating.
But lab experiments at Penn State found the real danger threshold is significantly lower. Young, healthy adults in controlled conditions hit their cooling limit at wet-bulb temperatures between 25°C and 31°C, depending on humidity levels. In hot, dry conditions, the critical threshold was as much as 10°C below the theoretical 35°C limit. This means that parts of the world are already regularly experiencing conditions where the human body struggles to cool itself, and the risk zone is much wider than scientists initially believed.
Higher baseline temperatures, combined with rising humidity from warmer oceans, are pushing more regions into this danger zone more frequently. A heat wave that would have been uncomfortable 30 years ago can now cross the line into genuinely hazardous, especially for older adults, outdoor workers, and people without air conditioning.
Multiple Causes, One Direction
The recent heat isn’t the result of any single factor. It’s a pileup. Decades of greenhouse gas accumulation have raised the planet’s baseline temperature. Record ocean warmth is feeding extra energy into the atmosphere. Cleaner shipping fuel inadvertently removed a small cooling effect. El Niño gave temperatures an additional short-term boost in 2023 and 2024. And a wavier, more sluggish jet stream is locking heat waves in place for longer stretches.
Each of these factors alone would make things warmer. Together, they explain why the last few years have felt not just hot, but record-shatteringly, relentlessly hot. NOAA estimated a 7% chance that 2025 would break 2024’s all-time record. Even falling short, 2025 ranked as the third-warmest year ever measured. The trend line points in one direction, and the primary lever is the concentration of heat-trapping gases, which continues to climb year after year.