Flood Basalt Volcanic Climate Disruptions: Dynamical and Radiative
Feedbacks on SO2 Emissions
Abstract
Volcanic flood basalt eruptions have covered 1000s of
km2 with basalt deposits up to kilometers thick. The
massive size and extended duration result in enormous releases of
climactically-relevant gases such as SO2 and
CO2. However, it is still unknown precisely how flood
basalt eruptions influence climate via eruption rates and cadence,
height of the volcanic plumes, and relative degassing abundance of
species like SO2. Once eruptions occur, the complex
interplay of photochemistry, greenhouse gas warming, changes to the
atmospheric circulation, and aerosol-cloud interactions can only be
properly simulated with a comprehensive global climate model (GCM). We
created an eruption scenario for the Goddard Chemistry Climate Model
(GEOSCCM) that emits SO2 in the near-surface atmosphere
constantly and four times per year an explosive eruption that emits much
more SO2 in the upper troposphere/lower stratosphere.
The eruption lasts for 4 years and emits 30 Gt of SO2
total. This corresponds to ~1/10th of
what may have been emitted during the Wapshilla Ridge eruption phase of
the Columbia River flood basalt eruption 15-17 Ma. We use a
pre-industrial atmosphere and otherwise modern initial and boundary
conditions. The massive flux of SO2 into the atmosphere
is quickly converted to H2SO4 aerosols.
Global area-weighted mean visible band sulfate aerosol optical depth
reaches 220 near the end of the eruption, comparable to cumulonimbus
clouds. This reduces the surface shortwave radiative flux by 85% and
top-of-atmosphere outgoing longwave flux by 70%. Contrary to our
expectations, we find that the climate warms during and immediately
following the eruption after a very brief initial cooling. Global mean
surface temperature peaks 3-4 years after the eruption ends with a +6 K
anomaly relative to a baseline simulation without the eruption.
Post-eruption regional temperatures, particularly near-equatorial
continental areas, see drastic rises of summertime temperatures with
monthly mean temperatures equaling or exceeding 40°C. These temperature
responses are radiative- and circulation-driven. The eruption warms and
raises the tropical tropopause, allowing a massive flux of water vapor
into the stratosphere. Stratospheric water vapor, usually
~3 parts per million reaches 1-2 parts per thousand.