Towards IPCC AR6: Open questions in chemistry-climate coupling What are the environment / sustainability questions that the highest levels of governments will ask ? Which of these requires input from ACC community ? Ozone depletion (recovering or not?) Air quality (local control? out of our control?) Climate change (is this just CO2?) Geoengineering the stratosphere (complexity?) Who will be asking these questions ? How ? When ? UNFCCC COP Related multi-lateral climate talks UNEP O3, LRTAP, … Thru IPCC AR6 or Special Reports, probably 2019+ (e.g., on AQ & Climate) Will the ACC community be able to answer ? N.B. Warning label, this is just Prather’s editorial viewpoint. 4 Jan 2010 0754h Towards IPCC AR6: Open questions in chemistry-climate coupling Michael Prather, UC Irvine CCMI 2014 May Lancaster UK

Carefully specify the question. Plan for what it takes to answer it. CCMI => AR6: M. Prather 20 May 2014 Lancaster What can CCMI do ? Carefully specify the question. Plan for what it takes to answer it. Design innovative experiments. Establish standard diagnostics to compare with observations (specific to Q) to diagnose model differences (sensitivities)

  How to build a robust understanding of future AQ ? CCMI => AR6: Innovative Experiments M. Prather 20 May 2014 Lancaster How to build a robust understanding of future AQ ? Global emissions alter atmospheric composition and thence baseline levels (lowest percentiles) of near-surface O3 and particulate matter (PM) Global changes in climate (e.g., temperature, water vapor, convection, lightning) also alter these baselines Climate-driven changes in the meteorological regimes over polluted regions can alter extreme air quality (AQX) episodes Climate-change alters the efficacy of local, controlled emissions to generate pollution within a governance region (e.g., AQMD, EU country) via T, q, biogenic VOCs, radiation. With all factors combined (as typical in most pubs) verification is effectively impossible, also is understanding model differences. An assessment approach needs to evaluate each of these pieces separately using observations/ensembles (HTAP 2010; IPCC, 2013).  

 How to build a robust understanding of future AQ ? CCMI => AR6: Innovative Experiments M. Prather 20 May 2014 Lancaster How to build a robust understanding of future AQ ? Global emissions alter atmospheric composition and thence baseline levels (lowest percentiles) of near-surface O3 and particulate matter (PM) (Young et a; 2013 ACP).  (surface) / ppb

CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster ACCMIP hourly surface O3 diagnostics: Model tests with full EU/US surface sites from J. Schnell et al 2014 ACPD++ , UC Irvine surface AQ O3 sites gridded for comparison with ACCMIPs Test 2000s decade of ACCMIP for: seasonal cycles diurnal cycles AQX (97th %ile) eastern US western

Bad years have: (1) most AQX, (2) largest episodes, CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster Mega-pollution episodes caused by continental-scale stagnation episodes: change with climate? Recent work on mapping out local climatologies of surface O3 show extensive, multi-day (mega) pollution episodes from surface sites, & possibly satellite. Air Quality Extreme (AQX) events [red 1x1 cells], when identified as 97%ile form mega-episodes, => matched by global model hindcast. Bad years have: (1) most AQX, (2) largest episodes, and (3) highest mean O3. ? Bad climates do also? US Climatology of O3 Air Quality & extreme episodes (AQX) 2000-2009.   2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 R2 AQX events (#) 13.5 11.5 16.5 15.0 4.6 11.2 13.3 8.1 1.7 1 AQX size (hkm2 d) 618 373 1239 581 82 435 515 186 70 32 0.78 O3 JJA (ppb) 49.3 49.4 51.4 50.1 45.5 48.8 50.7 47.5 46.2 43.7 0.96 Schnell ++, 2014 ACPD (current)

Serious Climate Change is just about the CO2. CCMI => AR6: Why chemistry matters M. Prather 20 May 2014 Lancaster Serious Climate Change is just about the CO2. With a “likely to avoid 2°C” cap of 1,000 GtC, and 500 GtC already spent, we have headroom of 500 GtC With CH4, O3, N2O, HFCs, the cap is only 790 GtC and then the headroom drops 42% to 290 GtC!

What is really going on in the stratosphere? N2O lifetime change CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster What is really going on in the stratosphere? N2O lifetime change from E. Fleming, GSFC Uncertainty in the future N2O lifetime is a major part of the IPCC AR5 range in future N2O abundances for a given scenario, impacting both climate and ozone.

Diagnosing lower strat vs. upper trop with a state variable like e90 CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster Diagnosing lower strat vs. upper trop with a state variable like e90 Use of artificial tracer e90 can diagnose tropopause (white line) and identify / separate many features such as folds, tubes, and even an undiscovered N-S systematic difference in O3: Prather, et al.,2011 JGR 116, D04306 O3 (ppb, annual) wrt tropopause height 50S-40S << 40N-50N +4 km 731 993 +1 km 147 234 tpp 118 203

CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster Where is the equator? a diagnostic definition based on atmospheric mixing from C. Holmes & M. Prather, UC Irvine Seasonal cycles of trop-hemisphere mass and trop-chemistry loss of CH4 CH4 column loss & mixing equator (30 days) Atmospheric-mixing equator defined as where NH and SH e90 tracers are equal (actually baroclinic). This equator moves with seasons & the monsoons On average 53% of the troposphere is in SH CH4 loss freq. is 25% faster in geographic NH CH4 loss freq. only 5% faster in atmos-mix NH MCF obs. only constrain this latter ! N.B. the Waugh-Orbe tracers (Orbe et al, 2013 JGR) are similar to the e90 tracers (Prather et al, 2011 JGR).

CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster Trop. chemistry has scales and variability not simply diagnosed as mean and std dev. How should model validation go after this? UCI CTM (T319L60) 16 Jan 2005 Loss O3 (ppb/day) Go after the key rates! Observe / diagnose those species needed to derive P/L – O3, L – CH4, …. Generate prob. distrib. and other statistics. Prod O3 (ppb/day) H2O2 (ppb on 720 hPa) Loss freq CH4 (/year) Loss freq CH4 (/year)

CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster What is the STE flux of O3 from strat to trop ? Where and when does it occur ? Can we even agree on how to calculate it in a model ? How to detect change ? It is exceedingly difficult to calculate the STE flux of O3 – even within in models, much less to “observe” it. All “measurements” are proxies. O3-tracer correlations is best integrative method. Tracer-tracer slope gives relative fluxes (Plumb & Ko,1992) When STE is diagnosed with high spatial and temporal resolution, we can identify (at least in the models) new processes that are linked to STE: e.g., continental convection in NH summer (Tang, 2011, GRL). Fig. Latitude‐longitude plot of mean deep convective fluxes (colored pixels at model resolution, hPa/s) and STE O3 fluxes (red contour lines, g/m2/yr) for JJA of 2005.

CCMI => AR6: New Diagnostics M. Prather 20 May 2014 Lancaster What is the STE flux of O3 from strat to trop ? Where and when does it occur ? Can we even agree on how to calculate it in a model ? How to detect change ? Three commonly used STE O3 flux diagnostics are compared within a single CTM running ECMWF IFS meteorology from very different versions: Cycle 29/31 & Cycle 36 (stagnant). Tropopause is diagnosed with e90 synthetic tracer. TC measures advective change in trop O3 column every step across an iso-surface. LS calculates monthly budgets for lowermost strat: 100 hPa to a lower iso-surface. WxO3 calculates flux across 100 hPa every step or using monthly zonal mean circ. the residual circ. monthly zonal means is [w*] x [O3] STE fluxes with TC and LS are similar, but [w*] does not even give interannual variability

CCMI => AR6: Innovative Experiments. M CCMI => AR6: Innovative Experiments M. Prather 20 May 2014 Lancaster How important is STE O3 flux? What is the lifetime of trop O3 from different sources (surface pollution, lightning NOx, STE)? Young et al 2013, ACP ΔτO3 We know that the perturbation lifetime for trop O3, depends on the source: Δτ = ΔB / Source Otherwise, why care about STE flux? (ΔτSTE > ΔτP ~ >> >>

is this schmutz ours or can we blame it on….? CCMI => AR6: M. Prather 20 May 2014 Lancaster forecast for LA clear skies, but is this schmutz ours or can we blame it on….? LA and HOLLYWOOD sign from UCIrvine 7 Mar 2010 1147h