1. Arctic ozone loss 2011 John Pyle Scientific Assessment Panel National Centre for Atmospheric Science, UK & Centre for Atmospheric Science Department of Chemistry University of Cambridge With thanks to Paul Newman, Martyn Chipperfield, Gloria Manney Michelle Santee and Markus Rex Side event to 23 rd MOP / 9 th COP, Bali 23 November 2011

2. Overview Polar ozone loss depends on temperature and inorganic halogen concentrations in lower stratosphere (depends on MP) Assessments in 1990s recognised that could have severe Arctic ozone depletion in very cold Arctic winters Very large ozone depletions previously reported in, e.g., 95/96, 96/97, 99/00, 04/05, 07/08 Low temperatures into spring are key ingredient for large ozone loss

3. Arctic 2011 Overview Stratospheric minimum temperatures in 2010/2011 were unusually low/long lasting Severe ozone loss (>80%), over a significant depth of atmosphere occurred. Some records established – but consistent with our chemical understanding But what is driving the low temperatures (natural variability vs GHG, say)?

4. Record Arctic Ozone Loss – 2010/11 Vortex Average Loss at 20km TOMCAT/SLIMCAT CTM Courtesy Martyn Chipperfield www.see.leeds.ac.uk/slimcat Over -85% loss in vortex Cold

5. Arctic Ozone Loss: SLIMCAT Results Arctic ozone loss is initially limited by the availability of sunlight in early winter and curtailed by the breakdown on the vortex in mid winter. Year-to-year variations of polar Arctic O 3 loss due to different meteorological conditions. Record Arctic polar ozone loss for 2010/11 (local maximum ozone loss is ~95% at 465K by 29 March 2011). Partial column ozone loss is ~175 DU. Courtesy Chipperfield,www.see.leeds.ac.uk/slimcat Updated from Feng et al. (GRL, 2007)

6. High levels of Activated Chlorine observed in Arctic in March 2011 Adapted from Figure 2 of Manney et al. (2011) - Aura MLS 2005-2010 ClO. Arctic ClO in 2011 was outside the range of the 2005-2010 winter observations, and comparable to Antarctic ClO.

7. As a result of the high Cl levels, there were large ozone losses Adapted from Figure 2 of Manney et al. (2011) Aura MLS 2005-2010 Ozone. Arctic Ozone in 2011 was outside the range of the 2005-2010 winter observations, and almost as low as Antarctic ozone.

8. Overview Stratospheric minimum temperatures in 2010/2011 were unusually low/long lasting Severe ozone loss (>80%), over a significant depth of atmosphere occurred. Some records established – but consistent with our chemical understanding But what is driving the low temperatures (natural variability vs GHG, say)?