Climatic Data - Climate Change: Identification and Projections - page 27

as a positive anomaly. In the absence of past or future data, the anomaly is
extrapolated by zero. In Figure 2.13 it is possible to discern the last three
high impact eruptions: Agung (1963), El Chinchon, (1982) and Pinatubo
(1991).
Figure 2.13. Indicator of volcanic activity