Volcanic Winter and Climate: When Eruptions Cool the World
The largest volcanic eruptions can do more than devastate their surroundings; they can cool the entire planet for years. By injecting gas high into the atmosphere, great eruptions create a veil that dims the sun, lowering global temperatures and disrupting weather and harvests across the world. From the year without a summer that followed Tambora to the super-eruptions of the distant past, volcanoes have repeatedly shaped the Earth's climate.
How eruptions cool the planet
The key to volcanic cooling is not ash but gas, especially sulphur dioxide. When a powerful eruption injects sulphur dioxide high into the stratosphere, it reacts to form a haze of tiny sulphate particles. This haze spreads around the globe and reflects sunlight back into space, reducing the amount of heat reaching the surface and cooling the planet, sometimes for years.
The year without a summer
The most famous example is the 1815 eruption of Tambora in Indonesia, the largest in recorded history. Its gas spread worldwide, and the following year, 1816, became known as the year without a summer. Across the Northern Hemisphere, summer frosts, failed harvests, and famine struck. The cold, grey weather even influenced the art and literature of the time, a vivid reminder of volcanism's reach.
Pinatubo and modern measurement
The 1991 eruption of Pinatubo in the Philippines was the first great climate-altering eruption to be measured with modern instruments. Its sulphur dioxide cloud lowered average global temperatures measurably for a year or two. Because scientists could track the effect in detail, Pinatubo became a key natural experiment in understanding how volcanic gas influences climate.
Super-eruptions and deep cooling
The greatest eruptions of all, the caldera-forming super-eruptions of volcanoes like Toba and Yellowstone, could cool the planet far more severely. The eruption of Toba in Indonesia, tens of thousands of years ago, is thought by some scientists to have caused a prolonged volcanic winter, though its exact effect on early humans remains debated. Such events are rare but potentially profound.
Volcanoes and mass extinctions
On the longest timescales, the most colossal volcanism of all, the flood basalt eruptions that built provinces like the Siberian Traps, released so much gas over such long periods that they are linked to mass extinctions. These events altered the atmosphere and climate on a scale that reshaped the history of life, showing volcanism as a force capable of changing the world.
Cooling and warming
While the short-term effect of large eruptions is cooling, volcanism also plays a role in the long-term carbon cycle. Over geological time, volcanoes release carbon dioxide, a greenhouse gas, helping to warm the planet and keep it habitable. The balance between this slow warming and the sudden cooling of individual eruptions is part of the complex relationship between volcanoes and climate.
A factor in Earth's future
Understanding how eruptions affect climate is important not only for interpreting the past but for the future. A large eruption today would temporarily cool the planet and disrupt agriculture and weather, with global consequences. Studying past events like Tambora and Pinatubo helps scientists anticipate the climatic effects of the next great eruption.
Explore on the map
From Tambora and Pinatubo to the supervolcanoes of Toba and Yellowstone, the eruptions that have shaped Earth's climate are scattered across the world's volcanic regions. Explore them on the interactive map — filter by region to see the volcanoes whose eruptions have reached beyond their slopes to cool the entire planet.