A wildfire needs three ingredients to spread: fuel, an ignition source and favourable weather. For much of Europe's history, those conditions rarely came together at the same time.
This summer, however, they have repeatedly aligned across the continent—from Norway in the north to France, Spain and Italy.
By July 26, more than 250,000 people had been evacuated across France and Spain as devastating wildfires spread. Spain also declared its first national wildfire emergency after blazes near Madrid and Ávila scorched vast stretches of land.
The key to understanding these fires lies in the atmosphere.
WHAT IS A HEAT DOME AND WHY IS IT PERSISTING?
High above the Earth flows the jet stream, a fast-moving band of winds that typically carries cool, moisture-laden Atlantic weather across Europe.
As the Arctic warms, the jet stream has become weaker and more erratic. At times, it splits into two branches—a phenomenon scientists call a "double jet." When this happens, a dome of high pressure can become trapped over Europe for days.
Within this high-pressure system, sinking air compresses and warms, much like air heating up inside a bicycle pump. The descending air suppresses cloud formation, allowing uninterrupted sunshine to heat the ground.
Research by Efi Rousi and Kai Kornhuber suggests these persistent double-jet patterns are closely linked to the increasing frequency of extreme heat across western Europe.
HOW DRY SOIL MAKES HEAT EVEN MORE INTENSE
Heat alone does not ignite forests, but it creates the conditions that make fires easier to start and spread.
Hot, dry air acts like a sponge, pulling moisture from vegetation and soil. Scientists describe this process using a measure known as vapour pressure deficit, which reflects how strongly the atmosphere draws moisture from the landscape. The greater this atmospheric "thirst," the faster plants and forests dry out.
A self-reinforcing cycle then develops.
When soil contains moisture, much of the Sun's energy is used to evaporate water. Once the ground becomes dry, that energy instead heats the surrounding air. The hotter air dries the soil even further, creating an escalating cycle of rising temperatures and increasing dryness.
As a result, forests become highly combustible, with vegetation drying to the point where it can ignite rapidly.
HOW LARGE WILDFIRES CREATE THEIR OWN WEATHER
The most intense wildfires eventually become powerful enough to influence local weather conditions.
Massive fires generate towering columns of hot air and smoke that rise high into the atmosphere. As the plume cools, moisture condenses around ash particles, forming towering thunderstorm clouds known as pyrocumulonimbus clouds.
These fire-generated storms can produce powerful, erratic wind gusts and even lightning. The strong winds carry burning embers far ahead of the main fire, igniting new blazes several kilometres away.
This explains how wildfires can suddenly jump highways or rapidly expand beyond containment lines, forcing authorities to enlarge evacuation zones within a short period.
IS CLIMATE CHANGE DRIVING EUROPE'S WILDFIRES?
Scientists increasingly use a field known as attribution science to determine how much climate change contributes to extreme weather. This approach compares today's climate with a hypothetical world that has not experienced human-driven greenhouse gas emissions.
Studies examining the June 2026 European heatwave concluded that such an event would have been virtually impossible without human-induced global warming and is now around 100 times more likely than it was two decades ago. Separate research published in 2026 also found that the extreme dryness fuelling these fires has become roughly nine times more likely.
Europe is warming at approximately twice the global average rate. As temperatures continue to rise, forests in regions such as Scandinavia—which were historically too cool and damp to sustain major wildfires—are becoming increasingly vulnerable.
Wildfires themselves are not new. What has changed is the atmosphere surrounding them—one that holds more heat, extracts more moisture from the land and steadily increases the likelihood of severe fires year after year.
