In Antarctic and Greenland ice cores, a major eruption or series of eruptions is revealed as a spike in sulfate concentration, showing that the release in form of particles was higher than any other eruption since. Also, analysis of the ice cores pinpointed the event to late 1452 or early 1453. The volume of expelled matter is more than six times larger than that of the 1991 Pinatubo eruption and would have caused severe cooling of the entire planet the following three years. The link between the sulphur spike and the Kuwae caldera is questioned in a 2007 study by Károly Németh, et al. proposing the Tofua caldera as an alternative source candidate.