What caused the disaster to the human racer after the Toba eruption?

Scientist estimate that the eruption may have ejected up 6,000 km³ of

The magma and the pulverized rock
and sufficient belerang gases to form 5,000 megatons of stratospheric sulfuric acid aerosols. The suspension of so much material in the earth’s atmosphere resulted in a volcanic winter the lasted all year long, every year for several years. 
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