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And this was half-bad, half-good news for early humans living in Africa.<\/p>\n
\u201cSulfate aerosols in the stratosphere are more effectively transported to the hemisphere that is experiencing winter,\u201d Park says. For our ancestors, this meant the Toba\u2019s sulfate veil drifted northwards and thinned over their heads slightly sooner than it would if the eruption happened in the northern summer. On the other hand, the Northern Hemisphere has far more land, which cools down faster and further than the ocean, so a northern-winter eruption must have cooled the globe a bit more than the same eruption in July. But overall, compared against the broader climate change trajectory, the Toba eruption was a rather mild disaster.<\/p>\n
\u201cThe eruption did cool and dry the region, just not to such an extent as to significantly threaten the survival of humans,\u201d Park argues. Across the 450-year window his team analyzed, eastern equatorial Africa was already sliding from a warmer, wetter regime into a cooler, drier one, tracking a natural cooling trend recorded in Greenland ice. Against that background, Toba\u2019s impact looks tiny. \u201cOur study shows that the magnitude of cooling and drying after Toba was much smaller, and within the natural range of variation in the last glacial\u2013interglacial cycles,\u201d Park says. \u201cHumans had already experienced and survived that.\u201d<\/p>\n
The limitation in Park\u2019s study is that Chala is just one lake. \u201cIt records the regional climate signals in eastern Africa, but it doesn\u2019t show the impact on the whole globe,\u201d Park explains. \u201cThere should be more studies using a similar approach, at more sites where the Toba ash is found.\u201d<\/p>\n
The team also hopes similar approaches will be used to learn more about other huge volcanic eruptions like Los Chocoyos in Guatemala and the Oruanui eruption in New Zealand 26,000 years ago. \u201cThey were not as big as Toba, but they were still super-eruptions. It would be interesting and exciting to see what happened,\u201d Park says.<\/p>\n
Science Advances, 2o26. DOI: 10.1126\/sciadv.adv6851<\/p>\n