The Volcanic Signal in Surface Temperature Observations

Climate records of the past 140 years are examined for the impact of major volcanic eruptions on surface temperature. After the low-frequency variations and El Niño/Southern Oscillation signal are removed, it is shown that for 2 years following great volcanic eruptions, the surface cools significantly by 0.1°–0.2°C in the global mean, in each hemisphere, and in the summer in the latitude bands 0°–30°S and 0°–30°N and by 0.3°C in the summer in the latitude band 30°–30°60°N. By contrast, in the first winter after major tropical eruptions and in the second winter after major high-latitude eruptions, North America and Eurasia warm by several degrees, while northern Africa and southwestern Asia cool by more than 0.5°C. Because several large eruptions occurred at the same time as ENSO events, the warming produced by the ENSO masked the volcanic cooling during the first year after the eruption. The timescale of the ENSO response is only 1 year while the volcanic response timescale is 2 years, so the cooling in the second year is evident whether the ENSO signal is removed or not. These results, both the global cooling and Northern Hemisphere continental winter warming, agree with general circulation model calculations.