Mystery. An observation that we cannot (yet) explain.

Enigma. An observation that, according to our understanding, should not have happened. (Related term: out-of-sample behaviour)

Proposal: To really improve understanding we should be targeting climate mysteries and enigmas (more than is happening now).

Monday, 24 March 14

Mystery. An observation that we cannot (yet) explain.

Enigma. An observation that, according to our understanding, should not have happened. (Related term: out-of-sample behaviour)

Proposal: To really improve understanding we should be targeting climate mysteries and enigmas (more than is happening now).

—> Search for Climate Response Enigmas and Mysteries (SCREaM)

Monday, 24 March 14

2 Feb – 15 Feb 2010

Li#le  gain  with  1.33  km  simula4on

Over-­‐predic4on  of  rainfall  over  mountain  slopes

But  TRMM  seems  to  be  underpredic4ng  over  steep  terrain  (Fig.  5a  of  Ma#hews  et  al.,  2013,  JGR:  The  effect  of  the  Madden-­‐Julian  Oscilla4on  on  sta4on  rainfall  and  river  level  in  the  Fly  River  system,  Papua  New  Guinea)

M. Hassim, Todd Lane

Traditional model test: the Case Study

Monday, 24 March 14

Williams et al., JGR, 2004

A mystery

Monday, 24 March 14

Transition to continental characteristics is captured by WRF

Does not involve: - CAPE - PBL thickness - aerosols

Mesoscale heterogeneity and frontal dynamics are key.

Coloured lines show WRF CRM simulations w/different

initial soundings.

+ TRMM at an island

◼︎ continental/ocean means

Mor

rison

sch

eme

Thom

pson

sch

eme

Robinson et al. 2011

Systematic trend in behaviour

Monday, 24 March 14

Max. elevation 3-18 m 18-112 m112-684 m684-4200 m

Larger island -->

<--

str

onge

r co

nvec

tion

Higher orography reduces convective strength

Monday, 24 March 14

Climate sensitivity, LGM vs. futuresomewhat enigmatic...

Crucifix 2006IPCC 2013 (Masson-Delmotte et al.)

Monday, 24 March 14

• Rohling et al. 2013: Paleo gives 2.2-4.8 °C (68%)• LGM suggests 2-2.5 °C most likely value but with low resolving power

(IPCC 2013)• Recent warming seems to imply ECS<3 °C (e.g. Otto et al. 2013, Stott et

al. 2013)• “Emergent constraints” on models (Sherwood et al. 2014, Fasullo and

Trenberth 2012) imply ECS>3 °C.

Climate sensitivity estimates beginning to diverge

IPCC 2013 Sherwood et al. 2014

Monday, 24 March 14

Enigma candidate 1: Equable Climates

Lunt et al. 2013 (Phil. Trans)

Land surface zonal/annual means

Monday, 24 March 14

Enigma candidate 1: Equable Climates

Fedorov et al. 2013: - early Pliocene SST gradients flat in both meridional and zonal directions!- cannot reproduce with CCSM3, but fudging with subtropical cloud albedo helps.

Monday, 24 March 14

Enigma candidate 2: Hydrologic cycle

Durack et al. (2012, Science)

See also: Wentz et al. 2007

Wet-get-wetter response over oceans 1950-2000 is captured by models, but at ~1/3 to 1/2 the amplitude.

Obs CMIP3 20thC

Monday, 24 March 14

Enigma candidate 3: Continental Drying

Sherwood and Fu (2014, Science)

A

B

Change by 2100, RCP8.5

Monday, 24 March 14

Enigma candidate 4: Tropical Expansion

Johanson and Fu 2009 (J. Clim)

See also Allen et al. (2012)

Obs

Monday, 24 March 14

Enigma candidate 5: Decadal Variability

Ault et al. (2013, J. Climate)

England et al. (2014, Nat. Clim. Change)

20-yr trend in Pacific trade windsis ~5-sigma

Monday, 24 March 14

SCREaM teams

• Choose worthy enigma(s) if any and form focus teams?• Teams could:

• cross usual disciplinary lines with focused objective• speed the development and rejection of hypotheses• propose new model experiments to explore possible

explanations for enigmatic behaviour• Benefits: possible acceleration of progress; improve credibility

of science by confronting weaknesses head on; interesting!• Weaknesses: unsure if enigmas are real and represent errors

in processes (as opposed to, e.g., missing carbon cycle feedbacks, misinterpreted data). Potentially a high-risk strategy.

Monday, 24 March 14