Volcanoes and Climate

Volcanic eruptions are among the most powerful natural events on Earth. While they are often studied for the immediate devastation they cause — lava flows, ash clouds, and tsunamis — their impact on global climate is equally significant, though far less visible.

When a large volcano erupts, it can inject millions of tonnes of sulphur dioxide and fine ash particles into the stratosphere, the layer of atmosphere between roughly 10 and 50 kilometres above the Earth's surface. These particles, known as aerosols, reflect incoming sunlight back into space, reducing the amount of solar energy that reaches the ground. The result is a temporary cooling of the Earth's surface.

The most dramatic example of this effect occurred in 1815, when Mount Tambora in Indonesia produced the largest volcanic eruption in recorded history. The following year, 1816, became known as the 'Year Without a Summer'. Temperatures across Europe and North America dropped sharply, crops failed, and widespread famine followed. Snow fell in June in parts of New England, and harvests were ruined across much of Western Europe.

A more recent example is the eruption of Mount Pinatubo in the Philippines in 1991. This eruption sent approximately 20 million tonnes of sulphur dioxide into the stratosphere. Over the following two years, average global temperatures fell by about 0.5 degrees Celsius. The cooling effect was measurable by satellite and confirmed by ground-based weather stations around the world.

However, the cooling effect of volcanic eruptions is temporary. Aerosols gradually settle out of the stratosphere over a period of two to three years, and temperatures return to their previous levels. This distinguishes volcanic cooling from long-term climate change driven by greenhouse gas emissions, which accumulates over decades.

Historically, periods of intense volcanic activity have coincided with crop failures, political upheaval, and even the collapse of civilisations. Some historians have linked the decline of the Roman Republic in part to a series of eruptions that disrupted agriculture across the Mediterranean.

Today, scientists use satellite monitoring and atmospheric sensors to track volcanic emissions in real time. Understanding the relationship between volcanic eruptions and climate helps researchers build more accurate climate models — and provides a natural analogue for proposals to artificially cool the planet by injecting aerosols into the atmosphere.