If your summer has felt unusually cool, you’re not imagining it, but the explanation depends heavily on where you live. While the planet as a whole continues to set heat records, specific regions can experience below-average temperatures during any given summer due to shifts in ocean cycles, changes in the jet stream, and persistent weather patterns that funnel cold air into places that normally bake. Here’s what’s behind that surprising chill.
The Globe Is Warming, but Your Region May Not Be
This is the central paradox. July 2024 was the warmest July in NOAA’s 175-year global record, running 1.21°C (2.18°F) above the 20th-century average. Asia, Europe, and Africa all posted their hottest Julys ever measured. North America came in second-warmest, with parts of Canada running more than 3°C (5.4°F) above normal.
Yet during that same month, the United Kingdom’s mean temperature was 0.5°C below its recent average. Iceland’s capital, Reykjavík, came in 0.7°C below normal. Parts of Argentina saw temperatures plunge more than 3°C below average for stretches of 10 days at a time. A record-warm planet and a locally cold summer are not contradictions. They’re the result of how heat gets distributed unevenly across the atmosphere.
How the Jet Stream Creates Cold Pockets
The jet stream, a fast-moving river of air high in the atmosphere, is the single biggest factor determining whether your summer feels hot or cool. When the jet stream flows in a relatively straight path from west to east, weather systems move through quickly. But when it develops deep waves or gets “stuck,” it can park a trough of cool air over one region for days or weeks while another region roasts under a ridge of high pressure.
These stuck patterns, called blocking events, happen when a dome of high pressure anchors itself over one area and forces the jet stream to detour around it. The result is that polar air spills unusually far south on one side of the block while heat builds on the other. If you’re on the cool side, your summer can feel more like early spring, with persistent clouds, rain, and temperatures 5 to 10 degrees below what you’d expect. The block can last long enough to define your entire perception of the season.
The El Niño to La Niña Shift
One of the biggest climate levers on the planet flipped recently. El Niño, the warm phase of the Pacific Ocean cycle that dominated through early 2024, ended in May 2024. By mid-summer, conditions had shifted to neutral, with La Niña (the cool phase) favored to develop, carrying a 70% chance of emergence by late summer or fall and a 79% chance of being in place by winter.
La Niña means cooler-than-average surface water across the eastern and central tropical Pacific. That cooler water reshapes weather patterns worldwide. Trade winds strengthen, rainfall patterns shift over Indonesia and the central Pacific, and the ripple effects alter the jet stream’s behavior over North America and Europe. During La Niña transitions, some mid-latitude regions experience cooler, wetter summers as storm tracks shift. The transition happened more slowly than forecasters initially expected, which meant its effects crept in gradually rather than arriving all at once.
The Arctic Oscillation and Polar Air
The Arctic Oscillation (AO) is a pressure pattern that governs how well cold air stays bottled up near the poles. When the AO is in its positive phase, a strong band of westerly winds keeps polar air locked in the Arctic. When it swings negative, high pressure builds over the Arctic and Greenland, weakening that barrier and allowing frigid air to spill southward into the mid-latitudes.
During negative AO episodes, even in summer, polar air masses can push surprisingly far south. The jet stream buckles, and regions that would normally sit under warm, settled conditions instead find themselves under a stream of cool, unstable air. You might notice this as a stretch of days where highs barely reach the low 70s (or even 60s) in places accustomed to 85°F or higher. These episodes don’t have to last all summer to color your experience of the season. A few well-timed cool spells during what should be peak heat can make the whole summer feel “off.”
The North Atlantic Cold Blob
A persistent patch of cooler-than-expected sea surface temperatures in the North Atlantic, sometimes called the “cold blob” or the North Atlantic Warming Hole, has been a recurring feature in recent years. This area, roughly south of Greenland and Iceland, bucks the global warming trend and stays anomalously cool.
Research from multi-model climate assessments shows this cold patch has real consequences for nearby weather. It shifts surface wind patterns in winter and increases cloud cover in summer. That extra cloud cover blocks incoming sunlight, producing an estimated shortwave cooling effect of about 3.6 watts per square meter over the region during summer months. That’s a meaningful amount of blocked solar energy. For the UK, Iceland, Ireland, and parts of northwestern Europe, this ocean feature can reinforce cooler, cloudier summers and partially explain why those areas sometimes buck the global heat trend.
Why Perception Matters Too
Human perception of temperature is relative. If last summer was a scorcher (and globally, the summers of 2023 and 2024 broke records in many places), a return to merely average temperatures can feel genuinely cold by comparison. Your body and your expectations both calibrate to recent experience. A summer that would have felt perfectly normal a decade ago can feel chilly after a string of unusually hot years.
Timing also plays a role. A cold snap during the Fourth of July weekend or during your vacation will stick in memory far more than a warm spell you slept through. If the coldest days of summer happened to land on the days you were outside the most, your mental summary of the season skews cool even if the monthly averages were close to normal.
Real-World Consequences of a Cold Summer
A cooler summer isn’t just a matter of comfort. Agriculture is highly sensitive to temperature timing. In 2024, widespread frost events in Australia’s Riverina region caused yield losses of up to 90% in canola, wheat, and barley, compounding existing drought stress and forcing farmers to cut damaged crops for animal feed instead of harvesting grain. Cool-season growing regions face a difficult bind: summers that are too hot damage crops, but unexpected cold snaps and frost can be equally devastating, leaving farmers with fewer options to adapt.
Energy use patterns also shift. A cool summer means lower air conditioning demand but potentially higher heating costs in shoulder months. Outdoor businesses, from tourism to construction, can see delays and reduced revenue. For gardeners, a cold summer means slower growth, delayed harvests, and sometimes outright crop failure for heat-loving plants like tomatoes and peppers.
What Ties It All Together
There’s rarely a single reason your summer feels cold. It’s typically a combination: a jet stream pattern that parked cool air over your region, an ocean cycle transition nudging storm tracks in your direction, and possibly a regional feature like the North Atlantic cold blob reinforcing the chill. These factors layer on top of each other. When two or three line up at once, you get a summer that feels markedly different from what the global averages suggest. The planet is warming, but weather is local, and the atmosphere is perfectly capable of delivering a cold, rainy July to your backyard while the rest of the world sweats.