Toba and its bipolar order

Toba is a volcano located in Indonesia on the island Sumatra. This massive volcano erupted some 74,000 years ago and left a crater that is about 50 kilometers wide. Expelled during the eruption was 2,500 cubic kilometers of lava. To put this into some perspective: this was 5,000 times larger than the Mount St. Helens eruption in 1980 in the United States. Toba's eruption was the largest on Earth in the last 2 million years.

We know that a somewhat 'smaller' (excusez le mot) eruption from Tamboro resulted in a measurable cooling of the climate for several years and 1816 is known as the 'Year without Summer'. So, what effect would Toba have had on the global climate and early humans?

The volcanic eruption threw huge clouds of ash and sulphuric acid into the atmosphere and up into the stratosphere, from where it spread across the entire globe in both the northern and southern hemispheres and fell down as acid rain. The ash has now been found in the ice of both the Arctic as well as the Antarctic[1].

“We have found the same series of acid layers from Toba in the Greenland ice sheet and in the ice cap in Antarctica. We have counted the annual layers between acid peaks in ice cores from the two ice caps and it fits together," explains glaciologist Anders Svensson, Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen. "This means that we can compare the ice cores from Greenland and Antarctica with a annual accuracy and thus combine our knowledge of climate change in the northern and southern hemispheres," emphasizes Svensson.

There has been much speculation about how such a huge eruption affected the climate. The giant clouds of sulphur particles that are thrown up into the stratosphere form a blanket that shields the Earth from the sun's radiation and this causes the climate to cool. But how much and for how long? Modelling has shown that such an enormous eruption could cause a cooling of up to 10 degrees in the global temperature for decades.

"In the temperature curves from the ice cores we can see that there is no general global cooling as a result of the eruption. There is certainly a cooling and large fluctuations in temperature in the northern hemisphere, but it becomes warmer in the southern hemisphere, so the global cooling has been short," explains Svensson.

But the eruption may still have had major consequences for nature, the environment and humans in large areas of Asia, where a clear layer of ash from the eruption has been found.

[1] Svensson et al: Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 kyr BP) in Climate of the Past Discussions - 2012