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Can Cirrus Cloud Thinning Cool Climate Without Severe Climate Side Effects? CEC14 Berlin Lawrence Jackson, Julia Crook & Piers Forster.

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Presentation on theme: "Can Cirrus Cloud Thinning Cool Climate Without Severe Climate Side Effects? CEC14 Berlin Lawrence Jackson, Julia Crook & Piers Forster."— Presentation transcript:

1 Can Cirrus Cloud Thinning Cool Climate Without Severe Climate Side Effects? CEC14 Berlin Lawrence Jackson, Julia Crook & Piers Forster

2 Jones et al. (2011) Stratospheric SO 2 Marine cloud brightening To return global mean temperature to some earlier state, precipitation is reduced by too much Regional variations Side effects e.g. Stratospheric O 3 depletion, whiter skies Partial solution e.g. ocean acidification Only temporary Geoengineering challenges

3 Mean high cloud cover from CloudSat/CALIPSO 2B-GEOPROF R04 & 2B-GEOPROF-LIDAR P1.R04 data sets for 2006–2011 (Mace et al., 2009) Cirrus clouds

4 Bismuth(III) Iodide (BiI 3 ) What do we know about cirrus cloud thinning? Homogeneous nucleation Requires high super-saturation levels Dominates ice crystal production T < -40 o C Heterogeneous nucleation Out competes homogeneous nucleation for water vapour Microphysics Geoengineering Introduce efficient heterogeneous ice nuclei Temperatures < T -40 o C Larger ice crystals with greater fall speed “Negative Twomey effect” (K ӓ rchar & Lohmann, 2003) (Mitchell & Finnegan, 2009) Climate model simulations Has potential to offset anthropogenic warming Requires optimum particle concentrations (Storelvmo et al., 2013)

5 This study focuses on climate impacts We adopt a simplified implementation in a GCM by modifying ice fall speed Does cirrus cloud thinning: Cool climate? Change precipitation over land? Cause regional variations in precipitation? Could it complement stratospheric SO 2 and MCB?

6 HadGEM2 CC run on HECToR & ARCHER Martin et al. (2011) The HadGEM2 family of Met Office Unified Model climate Configurations, Geosci. Model Dev, 4, AtmosphereOcean Vertical levels6040 Horizontal resolution (longitude x latitude) o by 1.25 o 1 o by ⅓ o - 1 o Global grid cells192 x x 216

7 Simulation design HadGEM2 forced with: Historical data RCP Geoengineering Control simulation is RCP4.5 Climate baseline is Assess impacts of geoengineering on climate means

8 Some results … Climate engineering by cirrus cloud seeding

9 Outgoing longwave radiation (Wm -2 )Outgoing shortwave radiation (Wm -2 ) Results – Changes in TOA radiation fluxes & cloud cover (2x fall speed) Cloud cover (%) Vertical profile of cloud cover (%)

10 Results - Cirrus cloud thinning TOA radiative forcing

11 Results – temperature & precipitation

12 Results – change in temperature CIRRUS x2 (-0.6 K) CIRRUS x4 (-1 K) MCB (-1 K)(1.5 K)

13 Results – change in precipitation rate (kg m -2 day -1 ) CIRRUS x2 (land 1.8%) MCB (land -0.2%) CIRRUS x4 (land 1.4%) (land 3.2%)

14 Results – effects of climate geoengineering TemperaturePrecipitation CIRRUS x4 MCB

15 A cooler climate without side effects? Conclusions But … Regional variations in impact – especially precipitation Is it scalable? In practice how would we know if it works? F ( Wm -2 ) delta T (K)delta P Land (%) CIRRUS x CIRRUS x MCB-2-0.2

16 Thank you

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