1. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Observational evidence for volcanic impact on sea level and the global water cycle 1. Arctic Centre, University of Lapland, Finland 2. Thule Institute, University of Oulu, Finland 3. PSMSL, Proudman Oceanographic Laboratory, Liverpool, UK Aslak Grinsted 1, J. C. Moore 1,2, S. Jevrejeva 3

2. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Outline Motivation Objectives Data Approach Results Conclusion

3. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Volcanoes and Climate Major volcanic eruptions can inject scattering aerosol into the stratosphere and thus impose a significant radiative cooling of the atmosphere. Motivation

4. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Volcanoes and Climate Source: Robock (2000) Volcanic eruptions and climate. Rev. Geophys.

5. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Volcanoes and changes in ocean heat content Gleckler et al. Nature 2005 Lasting effect From Hansen et al., 2002, JGR Short term effect

6. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Models of volcanic impact on sea level Major volcanic eruption ▼ Cooling of the world oceans ▼ Densification ▼ Sea level drop Nature, 2005

7. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Observational verification? Nature 2005 ? Can we quantify the impact of volcanic eruptions using observations?

8. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Major contributors to sea level rise

9. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Objective Estimate the effect of volcanic eruptions on observational sea level.

10. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Jevrejeva et al., Nonlinear trends and multi-year cycle in sea level records. Journal of Geophysical Research, 111, 2005JC003229, 2006. Data: www.pol.ac.uk/psmsl/author_archive/jevrejeva_et_al._jgr.html www.pol.ac.uk/psmsl/author_archive/jevrejeva_et_al._jgr.html Location of 1023 tide gauges included in this study. Data RLR sea level data from PSMSL (1023 stations) GIA corrections from Peltier (2001) SLP corrections 12 regions Global sea level (GSL) reconstruction (1807-2003)

11. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Virtual station spatial stacking Individual tide gauge records Regional average Binomial tree to illustrate the ‘virtual station’ stacking method. Top-node represents the regional average, bottom nodes the tide gauge records, and rest of nodes are virtual stations.

12. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Jevrejeva et al., Nonlinear trends and multi-year cycle in sea level records. Journal of Geophysical Research, 111, 2005JC003229, 2006. Data: www.pol.ac.uk/psmsl/author_archive/jevrejeva_et_al._jgr.html www.pol.ac.uk/psmsl/author_archive/jevrejeva_et_al._jgr.html Global sea level (GSL) reconstruction (1807-2003)

13. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Eruptions causing the largest radiative forcing since 1890 5 largest eruptions have been modelled to have an impact on sea level. We focus on these.

14. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Results Sea level surrounding 5 major volcanic eruptions and the average sea level in these 5 periods. The solid black curve shows detrended GSL (grey shows 95% confidence interval). Boxes show the median sea level (centre line of box) of the “Before”, “Rise” and “Drop” windows. Top and bottom edges show the 95% confidence interval of the median. Average impact of 5 major volcanoes on detrended GSL as observed in tide gauge records (solid black curve). Coloured lines show detrended GSL around the individual eruptions.

15. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 How robust is the result? Average impact of 4 major volcanoes (excluding the 1902 Santa Maria eruption) on sea level. Boxes show the median sea level (centre line of box) of the “Before”, “Rise” and “Drop” windows. Top and bottom edges show the 95% confidence interval of the median. Average impact of 9 major volcanoes on sea level weighted by global average stratospheric optical depth. Boxes show the mean sea level (centre line of box) of the “Before”, “Rise” and “Drop” windows with top and bottom edges showing the 95% confidence interval of the window mean. Thin green line shows detrended GSL, but weighted by Southern Hemisphere stratospheric aerosol optical depth.

16. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Difference between modeled and observed effect Church et al., 2005 Modeled sea levelObserved sea level Grinsted et al., 2007

17. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Summary We examine the average impact on observed GSL of the 5 volcanic eruptions with the largest stratospheric aerosol loading since 1890 We find that the initial response to a volcanic eruption is a significant rise in sea level of 9±3 mm in the first year after the eruption This is followed by a drop of 7±3 mm in the period 2-3 years after the eruption relative to pre-eruption sea level. We suggest that the mechanism is a transient disturbance of the water cycle with a delayed response of land river runoff relative to ocean evaporation and global precipitation that affects global sea level.

18. Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Grinsted et al., Volcanic impact on sea level and the water cycle, EGU 2008 Reference Grinsted, A., J.C. Moore, and S. Jevrejeva. 2007. Observational evidence for volcanic impact on sea level and the global water cycle, PNAS, Vol, 104, nr. 50, 19730-19734, www.pnas.org_cgi_doi_10.1073_pnas.0705825104