200th Anniversary of the ‘Year Without a Summer’

Two hundred years ago, the warm weather we typically associate with summer never materialized for large areas of the globe, including the eastern United States and Europe. As a result, 1816 has become known as the year without a summer.

This historic cold spell was caused by the eruption of Indonesia’s Mount Tambora in April 1815 – the most powerful volcanic eruption ever recorded. While it devastated the immediate area and unleashed a deadly tsunami, it was the the massive amounts of sulfur dioxide spewed out by the volcano that had far-reaching impacts on the global climate.

After an eruption, ash and debris can cool a region for a few days by blocking out the sun. However, extremely powerful eruptions – like Tambora – can send gas clouds into the stratosphere – an altitude above where our daily weather takes place. The stability of this layer of the atmosphere means the sulfur dioxide can linger there for several months. Moving around the globe easily at this level, the sulfur dioxide spreads out, reacts with water vapor, and forms sulfate aerosols. These reflect incoming solar radiation and increase the reflectivity of clouds, cooling surface temperatures.

The average global temperature in 1816, according to the UCAR, dropped 3°C. That may sound like a small number, but it had dramatic impacts, especially during the summer months. In the US, heavy snow blanketed parts of New England in June. Frost was reported as far south as Virginia through July. Then in August, after a brief reprieve, severe frost returned to many parts of the northeast. These unseasonable conditions caused widespread crop failures, livestock losses, famine, and disease. Ultimately, it forced many people to migrate west.

Europe suffered similar conditions, but also had excessive rainfall. Crop failures and price inflation for basic goods from Ireland to Germany lead to food riots in many cities. The gloomy weather also famously inspired many British and European writers. Mary Shelly, for example wrote Frankenstein while on vacation at Lake Geneva in Switzerland that summer.

Luckily, this dramatic – albeit natural – climate change was temporary. The aerosols eventually settled out of the atmosphere and sunlight returned. While the process that produced this moment in weather history was essentially the opposite of the runaway green house effect happening today, it is a great example of how sensitive the climate is to changes in atmospheric composition. It also shows how seemingly small changes in global temperature can have huge impacts on our lives.