Ancient 'Volcanic Winter' Idea Loses Steam
Biologist Michael Rampino and volcanologist Stephen Self proposed in the early 1990s, that the eruption of Mount Toba in northern Sumatra set off a global "volcanic winter" and provoked a thousand years of lethally cold climate. Other researchers identified a corresponding human "genetic bottleneck" that suggests that our numbers may have been reduced to just a few thousand mating pairs.
This story has intrigued researchers for the better part of 20 years now. At some level, it reminds us of the human condition we share, how we are essentially dependent on the planet — perhaps how we are all children of the survivors of this great geologic catastrophe.
What I like about it especially, is the way it brings together the talents and technologies of so many different scientists — geologists and volcanologists, archeologists and anthropologists, geneticists and biologists, atmospheric scientists and climate modelers — all zeroing in on this singular, mysterious episode near the dawn of modern human development.
Alas, the same science that can envision such a story, when put to the test also has a way of rudely dashing ideas with cold water. The enormity of the eruption is not in doubt so much as the story of its impacts on the climate, humans, and their habitat.
In the late 1990s, ice cores drilled in Greenland, revealed that the thousand-year cold snap really began several thousand years after the Toba eruption.
Now the "volcanic winter" idea is also losing steam. Climate modelers led by Claudia Timmreck of the Max-Planck Institute in Germany, reported this week at the annual meeting of the American Geophysical Union that the eruption caused only a modest impact on the well-being of the human population 74,000 years ago. They found shorter and weaker temperature affects on the atmosphere and a smaller climate response in general.
The existence of a genetic bottleneck is still a matter of debate.
While estimates of the Toba eruption vary, no one has yet challenged that the eruption was bigger than anything else in the last 2 million years — bigger than Krakatoa and Tambora and Pinatubo and Mount St. Helens put together. And the idea that it made life miserable for humans and other creatures at least for a few years is entirely plausible.
PHOTO: Landsat image of Lake Toba, what's left of the volcano today.