1. ACCMIP simulations of Climate Change impacts on CO-tracer transport Ruth Doherty, Ian Mackenzie U. Edinburgh Paul Young, Oliver Wild U. Lancaster Mieyun Lin GFDL, Michael Prather UCI, ACCMIP modellers … ACITES York, Dec 2 nd 2013

2. Uses of a CO-Tracer What can a passive CO-tracer with a 50-day lifetime tell us about transport in a CCM? What are its strengths and weaknesses? Can we use this CO-tracer to create a metric of vertical overturning in the troposphere? Focus on climate change effects on transport …

3. First …CO tracer results from HTAP (TP1x)

4. CO tracer results from HTAP for Present and Future Climates Implemented a CO tracer for a species with a 50 day lifetime emitted as for CO over the NA, EU, EA and SA source region Two chemistry-climate models STOC- HADAM3 and UM-CAM both driven by the same SSTs from the HadAM3 GCM Results for 5-year (10-year) 2000s and 2100s climates

5. CO-Tracer results from NA 5 year (10-year) annual-average surface NA CO tracer concentrations for 2000 climate Difference in 5-year annual-average surface CO-tracer concentrations between the 2095 and 2000 climates In the future climate, less CO tracer from NA remaining at the surface especially over the Great Plains region but more over the E. and W. United States and outflow regions

6. And for other regions… Similar results for the other three HTAP regions Distinct patterns of adjacent areas of lower and higher surface CO tracer concentrations Shift in circulation within all the regions that extends across the regional boundaries between present day and future But only one representation of climate change…. Full vertical picture

7. Atmospheric Chemistry & Climate Model Intercomparison Project (ACCMIP) Another model intercomparison with a focus on climate change Only “CO-direct”- a tracer with a 50-day lifetime emitted form all CO emission sources across the globe Direct= emissions from fossil and bio fuel combustion, biomass burning, plant and soil release Present-day = ACChist= “2000s” ~10 years (SST climatology) Future = RCP 8.5 “2100s” ~10 years (SST climatology

8. Surface annual-mean CO tracer concentrations for 2000s Like CO sources 

9. Surface annual-mean CO_T: 2100s-2000s (2000s-1990s) Shifts in surface patterns over major source regions Some model to model similarities (eastern USA, S EU) and some differences → some evidence of reproducibility of shifts Signal larger than decadal variability (as in CMAM) Causes?

10. Surface annual-mean CO_T: 2100s-2000s (2000s-1990s)

11. Zonal-mean CO-tracer decadal mean 2000s (top) Diff CO-tracer decadal mean 2100s-2000s (bottom) Reasonable agreement  Surface –general decreases strongest at Equator (up to 5-10 ppb), increases 10°N & 30°N (up to 2-5 ppb) UT- tropics reductions of 1-2ppb (up to 5 ppbv) – weaker Hadley circulation signal? UT- extra-tropics esp NH- enhanced STE /higher tropopause (Fang et al. 2011 JGR)

12. Co-tracer decadal mean 2000s 1000-900hPa average (top) and 400-200 hPa average (bottom) Fairly similar patterns across models

13. Gradient co-tracer (1000-900)-(400-200) hPa 2000s (ppb) Positive values over emission source regions and nearby outflow Negative values for outflow especially S. Hemisphere Similarish picture in 2100s (not shown)

14. Difference 2100s-2000s co-tracer (1000-900) hPa (top) and 400-200 hPa (bottom) At 1000-900 hpa: mixed signal N and S of equator (global mean decreases but with N. Africa and Asia increases) At 400-200 hPa: tropical signal more uniform across hemispheres (large decreases) and large increases at N. poles (STE, higher tropopause)

15. Difference 2100s-2000s co-tracer gradient (1000-900)-(400-200) hPa gradient increases over tropical land but decreases elsewhere especially northern polar latitudes Tropics: co-tracer gradient strengthens over emission regions (Fang et al. suggest reduced convective mass flux)

16. Vertical overturning? Model nameUM-CAMGISS NCAR- CAM3.5 CMAMSTOC-HadAM3 Global-mean gradient co- tracer 2000s/2100s 7.84 7.01 8.10 7.74 7.01 6.22 7.69 7.46 6.28 6.12 % change fut-pres -10.5% -3.4% -11.3% -3.0% -2.5% 30°S-0° gradient 2000s/2100s Change 2100s-2000s (land) 2.1 1.6 -0.5 (-0.4) 4.2 4.9 -0.7 (3.5) 1.4 0.23 -1.2 (-1.9) 1.5 2.2 -0.7 (2.8) 1.0 0.75 -0.25 (-0.32) 15°S to 15°N 2000s/2100s Change 2100s-2000s 12.0 11.5 -0.5 (-1.8) 14.6 16.1 1.5 (5.2) 13.9 13.1 -0.8 (-0.6) 13.1 13.9 0.8 (4.2) 12.9 0.0 (-0.2) 0°-30°N gradient 2000s/2100s Change 2100s-2000s 16.9 16.7 -0.2 (0.4) 17.6 18.5 0.9 (3.5) 16.1 16.2 0.1 (2.0) 18.2 19.4 1.2 (5.0) 15.4 16.3 0.9 (1.9) 30°N-60°N gradient 2000s/2100s Change 2100s-2000s 19.1 17.2 -1.9 (-2.1) 16.9 14.9 -2.0 (-1.8) 18.9 17.6 -1.3 (-1.7) 19.8 18.0 -1.8 (-1.5) 14.3 14.5 0.2 (0.5) 60°N-90°N gradient 2000s/2100s Change 2100s-2000s 9.3 6.0 -3.3 (-3.4) 8.1 4.5 -3.6 (-3.6) 11.9 10.0 -1.9 (-1.9) 13.4 10.2 -3.2 (-3.4) 8.5 5.9 -2.6 (-2.7)

17. Conclusions Shifts in circulation patterns of surface CO-tracer around major emission source regions Largest CO-tracer decreases in tropics -weaker Hadley circulation but confined areas of increased CO-tracer at the Equator also (convection scheme?) Large uniform increases in northern mid-latitudes upper troposphere and reduced LT-UT gradient Mixed gradient changes over tropics- increases over N. tropical land Contributions from changes in tropopause height/STE and from changes in upwelling

18. Seasonal (MAM and JJA CO-T changes: 2100s-2000s (2000s-1990s) UM-CAM, GISS similar between seasons, more increases in tropics in JJA CAM 3.5 very different in tropics

19. Fang et al. (2011) JGR 20 year average zonal mean distribution of CO tracer (unit: ppbv) during 1981–2000 (black solid contour) and the changes of that tracer from 1981–2000 to 2081–2100 (color shaded) Blue dashed and dotted lines show the tropopause location during 1981–2000 and 2081–2100, respectively Only changes significant at the 95% confidence level are shown

20. Vertical overturning Model nameUM-CAMGISS NCAR- CAM3.5 CMAM STOC- HadAM3 Michael’s suggestion 1. emiss_co 4 *area: total over all grid boxes (kg s-1) 18819.8 19622. 4 19344.519307.019327.1 2. emiss_aco / Mass air (normalised to a 125m cell height) ratio Mair/MCO: mean (ppb day-1) 2000s/2100s 23.54 24.05 24.44 24.75 23.48 23.76 23.94 24.36 24.27 24.72 3. diff (925-325 hpa) 2 co-tracer: mean of all grid cells (ppb) 2000s/2100s 3.68 3.64 4.60 4.41 3.23 2.83 4.47 4.85 4.02 4.07 4. mean grad co- tracer (ppb) /mean(emiss co in ppb day- 1)**(days) 0.157 0.151 0.188 0.178 0.137 0.119 0.187 0.199 0.165 0.173 5. diff fut-pres of 11.(day) and (%) -0.005 (-3.2%) -0.010 (- 5.4%) -0.018 (- 13.2%) +0.012 (+12.4 %) +0.007 (+4.3%) 6. Fang et al. relative change in the COt gradient change but between 925hPa and 325hPa and (2 nd left term)*** -2.7%-4.3%-12.5%+8.9%+2.4% Results from ACCMIP monthly data: italics = rcp 8.5, nonitalics = acchist 2000 – 10 years Notes: 1 cmam and stoc-hadam3 are very slightly different. 2 nearest model layer to 925 and 325 hpa (not much divergence between models)- need to interpolate **~3ppb/~24 ppb/day=0.14-0.19 days- 3.x hours seems not sensible. Not sure that this division tells us truly about transport between the two levels- would lifetime (50days) not come in? (checked emission field in ppb looks sensible) *** Fang et al. use lifetime and a 2 box model for the LT and FT. I’ve calculated the same relative change in the COt gradient change but between 925 - 325 hPa. (They calculate FT-LT ) Message: Both methods give a similar idea about global mean changes LT-UT of (range -13% to +10/2%) but these are the combined result of different responses in tropics and high latitudes (be nice to separate tropics especially land tropics but not sure of validity) Fang Y., A. M. Fiore, L. W. Horowitz, A. Gnanadesikan, I. Held, G. Chen, G. Vechhi, H. Levy (2011) Impacts of changing transport and precipitation on pollutant distribution in a future climate, J. Geophys. Res.>, doi:10.1029/2011JD016105.