What name is given to the unusually cold climate of 1816 caused partly by the Mount Tambora eruption?

The unusually cold climate of 1816 was called the Year Without a Summer.

The main trigger was the massive April 1815 eruption of Mount Tambora in present-day Indonesia. The eruption injected sulfur dioxide and other material into the stratosphere, where sunlight-reflecting aerosols spread around the planet. This reduced incoming solar energy and disrupted weather patterns during the following year.

In parts of Europe and North America, summer frosts, persistent rain, crop failures, and food-price increases were reported. Snow fell in some areas during months that normally bring warmer conditions. The effects were especially severe around the North Atlantic region.

The phrase does not mean that every place had no summer at all. Regional weather varied, and natural climate variability also contributed. The event is often remembered as one of the clearest examples of a volcanic eruption producing short-term global cooling.