If another catastrophic, caldera-forming Yellowstone eruption were to occur, it would probably alter global weather patterns and have enormous impacts on human activity (especially agricultural production) for many years. At this time, however, scientists do not have the ability to predict specific consequences or durations of possible global impacts from such large eruptions.
The 1991 eruption of Mt. Pinatubo in the Philippines was about 1,000 times smaller than Yellowstone’s largest known eruption; it caused temporary, yet measurable, changes in global temperatures. The sulfur dioxide emitted from the volcano interacted with the atmosphere, which cooled the Earth’s surface for three years following the eruption. At the height of the impact, global temperatures dropped by 1.3 degrees Fahrenheit (0.7 degrees Celsius).