A new paper in Nature Geoscience by Santer and colleagues revisits the volcanic scenarios used in modern climate model simulations. The authors consider the effects of including a ‘more realistic’ model for the influence of small volcanic eruptions on the climate system over the past two decades. Of course, more realistic means more difficult.. and one of the long-standing and unresolved problems with small volcanic eruptions is that not only are they small, but their consequences are unpredictable. These complications arise, in part, from the fact that the part of the volcanic system that is responsible for the climate impact are the emitted gases (notably, sulphur dioxide or SO2), and not the volcanic ash. In real volcanoes, these two parameters don’t seem to be very well correlated – and it has been well known for some time that small but explosive eruptions of sulphur-rich magmas might well have a disproportionate effect on the climate system (see, for example, Rampino and Self, 1984; Miles et al., 2004). For this reason, models of volcano-climate impact that only use information on eruption size (as measured by the Volcanic Explosivity Index) will usually only be a poor approximation to reality. A better representation might instead be a volcanic sulphur dioxide climatology, building on the extensive work of the volcanic emissions satellite-remote sensing community since the first volcanic plume satellite measurements in 1979. The currently most up to date compilations of volcanic SO2 emissions since 1996 can be found in Carn et al., (2003) and McCormick et al., (2013).
Reading between the lines, it looks as though Santer and colleagues have come to a similar conclusion – finding that their model simulations get a little closer to observations of tropospheric temperature trends when they introduce a ‘realistic’ volcanic scenario to simulate the past 25 years of eruptions. What a pity that the volcanic dataset they relied on to line up particular eruptions with aerosol optical depth perturbations was patched together from secondary sources. Clearly, as they suggest, more work is needed – but why not start by bringing the climate modeling community and volcanologists together to find out what we each think that we know ?
Carn SA et al. 2003 Volcanic eruption detection by the Total Ozone Mapping Spectrometer (TOMS) instruments: a 22-year record of sulphur dioxide and ash emissions, In: Oppenheimer et al. (eds), Volcanic Degassing, Geological Society, London, Special Publications 213, 177-202.
McCormick BT et al. 2013 Volcano monitoring applications of the Ozone Monitoring Instrument, In: Pyle DM et al. (eds), Remote Sensing of Volcanoes and Volcanic Processes, Geological Society, London, Special Publications 280, 1259-291.
Miles GM, Grainger RG and Highwood EJ 2004 The significance of volcanic eruption strength and frequency for climate Q. J. R. Met. Soc. 130 2361–76
Rampino MR and Self S 1984 Sulphur-rich volcanic eruptions and stratospheric aerosols, Nature 310, 677 – 679
For more information on William Hamilton and Vesuvius, try this delightful blog post by Karen Meyer-Roux.