Theory 27/Earth, Climate & Energy /Volcanology
Volcanic Winter Is an Altitude
Impact is ranked by erupted mass. The number that matters may be the height.
The climate impact of an eruption is set by whether its sulfate reaches the stratosphere rather than by the mass erupted, so a moderate eruption that penetrates the tropopause can cool more than a larger one that does not.
01The evidence
Historical eruptions with similar masses produced very different climate effects, and the differences track injection height.
02The tension
Impact estimates use erupted mass and sulfur content, which predict cooling from the amount and treat altitude as a modifier.
03The mechanism
Sulfate aerosols cool only while they reside in the stratosphere, where they are not rained out. An injection below the tropopause has a residence time of days; above it, of years.
That makes altitude the determinant, and predicts a threshold in injection height rather than a smooth scaling with mass.
04What this is not
Those models scale with erupted mass. This scales with residence, which explains the mismatch.
05Predictions
- P1Cooling should depend on stratospheric injection.
- P2Moderate penetrating eruptions should outperform larger shallow ones.
- P3A threshold should appear at the tropopause.
06Refutation
Cooling scaling with mass at controlled altitude would restore the mass model.
07What it changes
It would change eruption impact assessment.