The 1783 Laki eruption in Iceland would have had a dramatic effect on clouds
The 1783–1784 AD Laki flood lava eruption in June 1783 lasted for 8 months and released 122 Tg of sulphur dioxide gas into the upper troposphere and lower stratosphere above Iceland. We have used GLOMAP to study the impact of the eruption on cloud condensation nuclei (CCN) – that aerosol particles that can form cloud drops.
We calculate that total particle concentrations in the free troposphere increase by a factor similar to 16 over large parts of the Northern Hemisphere in the 3 months following the onset of the eruption. Particle concentrations in the boundary layer increase by a factor 2 to 5 in regions as far away as North America, the Middle East and Asia due to long-range transport of nucleated particles.
CCN concentrations (at 0.22% supersaturation) increase by a factor 65 in the upper troposphere and up to a factor 26 in the boundary layer near the surface. Averaged over the Northern Hemisphere, the eruption caused a factor 4 increase in CCN concentrations at low-level cloud altitude.
The simulations show that the Laki eruption would have completely dominated as a source of CCN in the pre-industrial atmosphere. The model also suggests an impact of the eruption in the Southern Hemisphere, where CCN concentrations are increased by up to a factor 1.4 at 20 degrees S.
The simulations show that the microphysical processes leading to the growth of particles to CCN sizes are fundamentally different after an eruption when compared to the unperturbed atmosphere, underlining the importance of using a fully coupled microphysics model when studying long-lasting, high-latitude eruptions.
What does all this mean for the climate at the time? These calculated changes in CCN are enormous: larger than caused by modern day air pollution. So Laki would have had a temporary but very large effect on climate, through changes in clouds. Our follow-up work will quantify changes in cloud drop concentrations.
We are interested in eruptions like Laki also because they are small examples of much larger flood lava eruptions that have been implicated in extinctions.
You can read Anja Schmidt’s paper at http://www.atmos-chem-phys.net/10/6025/2010/acp-10–6025-2010.html
See also Anja’s page at http://homepages.see.leeds.ac.uk/~ear5as/research.html