Climate forcing volcanic eruptions: future extreme event occurrence likelihoods

Transcription

1 Climate Change and Extreme Events: Managing Tail Risks Workshop 2 3 February 2010 Washington DC Climate forcing volcanic eruptions: future extreme event occurrence likelihoods Willy Aspinall with apologies for absence (Willy.Aspinall@Bristol.ac.uk) and acknowledgments to Alan Robock for some material

2 Santorini, 1628 BC Etna, 44 BC Laki, Tambora, 1815 Toba, 71,000 BP Famous Volcanic Eruptions Krakatau, 1883 Pinatubo, 1991 El Chichón, 1982 St. Helens, 1980 Agung, 1963

3 Tambora in 1815, together with an eruption from an unknown volcano in 1809, produced the Year Without a Summer (1816)

4 Anomaly ( C) Tambora in 1815, together with an eruption from an unknown volcano in 1809, produced the Year Without a Summer (1816) Global Surface Temperature Reconstruction Year Mann et al. (2000)

5 Important Research Questions How do quiescent emissions change over time? What is their current source strength? Explosive eruptions are not the only volcanic source to the atmosphere. While quiescent emissions have regional rather than global impacts, they are important in the context of anthropogenic tropospheric aerosols [Graf et al., 1997]. If the source strength changes significantly over time, this can produce large regional climate changes. More monitoring of the chemistry and magnitude of continuing quiescent emissions will be essential if we are to understand issues such as the impact of anthropogenic aerosols. From Blowin in the wind (Robock, 2002)

6 Important Research Questions How do high-latitude eruptions affect climate? Most research on the impacts of volcanic eruptions on climate has focused on tropical explosive eruptions, such as the recent 1963 Agung, 1982 El Chichón and 1991 Pinatubo eruptions. But there have been larger highlatitude eruptions in the historic past that have also had profound influences, the most notable recent one being the 1783 Laki fissure eruption in Iceland. The eruption affected air quality and climate for most of the Northern Hemisphere. If it occurred today, it could halt air traffic for 6 months [Thordarson and Self, 2002]. Questions that still need answers include whether high-latitude eruptions can affect the climate in the other hemisphere, and what the effects would be of eruptions from high latitude Southern Hemisphere volcanoes. From Blowin in the wind (Robock, 2002)

7 Important Research Questions How can we better quantify the record of climatically significant volcanism? To measure the natural climatic forcing from volcanic eruptions for the past, so that we may place anthropogenic climate change in context, we need a better record of the frequency and magnitude of past eruptions. Unlike many other attempts to reconstruct past climate and its forcing, the evidence from past volcanic eruptions is preserved in ice cores, waiting for us to analyze it. A major advance to allow better interpretation of the location of eruptions that produce ice core signatures would be better atmospheric models of transport and deposition that could trace sulfate aerosols from the vent to the ice. From Blowin in the wind (Robock, 2002)

8 POT extreme value fitting to different eruption magnitude datasets (from Deligne et al., 2010) Note short historical records (Table 4) significantly under-predict largest known geological eruption (Fish Canyon Tuff - magnitude 9.1 / 9.2)

9 Predicted return periods for selected eruption magnitudes, using different POT thresholds (from Deligne et al., 2010)

10 Estimated probability of occurrence of another Tambora (1815) year without summer eruption magnitude 6.9 or greater in next 40 and 90 years (pace IPCC, and Keith et al Nature Opinion; following Deligne et al. (2010) mean eqns 8, 9 parametertables 5, 6 assumes Poissonian arrivals) Time Magn = yrs 90yrs Prob Prob Est. return period = 288 years (POT model threshold u = 4) Est. return period = 438 years (POT model threshold u = 5.5)

11 An alarming inference from the POT model The u = 4 Holocene data model predicted 0.01 prob (1%) event in 90 years has eruption magnitude ~7.7 i.e. larger than any in the Holocene record (last 10,000 years). This would be similar in size to the Toba eruption (74,000 years ago) which produced ~2,800 cubic kilometres of ash, more than 2000 times the amount generated by the 1980 eruption of Mt. St. Helens! This magnitude would put it in the super-eruption class, and is possibly the right order of size for a future Yellowstone eruption. Note: the related uncertainty on this magnitude prediction is very large, and the central value equivalent ret. period (9,500 years) is at considerable odds with previous, less statistically-informed return period guestimates which suggest Toba-size eruptions have a return period of 100,000 years!