EPS 231, Climate dynamics Eli Tziperman; Museum building 456, 24 Oxford St. 617-3848381; eli@eps.harvard.edu TF: Lauren Kuntz <lkuntz@fas.harvard.edu> Course web page, teaching notes, downloads: http://www.seas.harvard.edu/climate/eli/Courses/EPS231/2017spring/ Textbooks: Vallis: Atmospheric and oceanic fluid dynamics Dijkstra, nonlinear physical oceanography, Hartman, global physical climatology Strogatz, nonlinear dynamics and chaos, Needed background: basic Fluid dynamics/ GFD (MIT12.800, EPS 131/132/232, engineering fluid dynamics, etc) Odyssey account: apply now! For GCM analysis experience Requirements: HW every 9-10 days (50%); final project (50%)

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Outline Energy balance: multiple equilibria, small ice cap instability, relevance to recent Arctic sea ice melting & Snowball Earth El Nino: (4 yrs) delayed oscillator, stochastic & chaotic irregularity, teleconnections via stationary Rossby Waves THC: (50-200 yrs) Multiple equilibria, abrupt transitions, advective & convective feedbacks, variability & oscillations Dansgaard-Oeschger & Heinrich events: (103-104yrs) due to THC variability and ice sheet collapses. Glacial cycles: (105 yrs) mechanisms, Milankovitch, CO2, ice Warm climate: (3-5x106 yrs, Pliocene), permanent El Nino Equable climate: (50x106 yrs, Eocene) Hadley cell, hurricanes, polar stratospheric clouds, convective cloud feedback. Tools: observations, proxy observations, hierarchy of modeling tools from conceptual (toy) models to hands-on GCM analysis.

EPS 231, Climate dynamics, review!

Energy balance, small ice cap instability Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Energy balance, small ice cap instability Small ice cap instability: Polar ice cap can only be sustained if over a minimal size roughly corresponding to present-day arctic sea ice cover. Run away ice albedo, snowball events: Ocean frozen to a depth of ~1km, land ice-covered for Myrs Termination due to co2 emissions from volcanoes? Initiation trigger? Evolutionary consequences? Predicted by Budyko-Sellers (1969) energy-balance toy model

El Nino – Southern Oscillation (ENSO) Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate El Nino – Southern Oscillation (ENSO) Sea surface temperature, 1997: strongest El Nino in 100 years Mechanism: ocean waves, thermocline, SST; atmospheric heating, winds; & ocn - atm coupling

ENSO ENSO is irregular (nino3 SST), yet locked to seasonal cycle Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate ENSO ENSO is irregular (nino3 SST), yet locked to seasonal cycle teleconnections

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate ENSO Equatorial waves Ocean-atmosphere coupling: SST  wind  thermocline depth  SST Delayed oscillator, role of delayed Rossby waves Irregularity: Transient amplification/ stochastic optimals Chaos: quasi-periodicity route to chaos driven by seasonal cycle Teleconnections, atmospheric RW, ray tracing, WKB Final review

Thermohaline circulation (THC/MOC) Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Thermohaline circulation (THC/MOC) Transport: 20 x world rivers combined. Warms Europe…? Driven by temperature & salinity gradients + more Can become unstable, multiple equilibria, hysteresis, … affects climate on a hundred-year time scale A winter scene in Europe's Little Ice Age, 14th Century Pieter Breugel the Elder.

THC: Little ice age, medieval warm period Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate THC: Little ice age, medieval warm period Norse ruins from Brattahlid, Greenland. “Eirik the Red,” exiled from Iceland for his crimes, 980 A.D., set sail and spotted “Greenland”. 1,000 Scandinavians lasted until 1480 A.D., died by starvation due to nasty winters.

THC/ MOC Stommel box model, multiple equilibria, hysteresis Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate THC/ MOC Stommel box model, multiple equilibria, hysteresis Convective and advective thermohaline feedbacks Variability mechanisms: Convective oscillations, Welander’s flip-flop and friends Advective oscillations Self-sustained oscillations vs noise driven (transient growth, stochastic optimals) Relaxation oscillations of the THC/ MOC Final review

Dansgaard-Oeschger Events Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Dansgaard-Oeschger Events DO events in Greenland ice cores: Warmings occur every ~1500yr ~10 deg C warming Start & end within 20 yrs! Warmings last 500-1000 yrs Mechanism: THC + sea ice?

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Heinrich events Ice Rafted Debris (IRD) sediment layers due to massive glacier discharges from Laurentide & other ice sheets, every 7-10,000 yr. Occurred 20-60,000 ago Possibly synchronous collapses/ discharges of several ice sheets Cold/ warm periods seen in ice core record as part of a Heinrich cycle… Mechanism: Bing/purge + THC + sea ice? Typical sediments Ice rafted debris

Dansgaard-Oeschger & Heinrich events Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Dansgaard-Oeschger & Heinrich events Observations: ice cores and sediments MOC/ THC flushes Amplification of atmospheric response by sea ice changes Precise clock behind DO events? DO teleconnections Heinrich events: basal melting and binge-purge mechanism Final review

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Largest climate signal in past 3Myrs. Still not understood: Mechanism/ forcing? What caused CO2 to change? Role of Milankovitch forcing? Ice flow basics

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Glacial cycles, more Why the transition from 40kyr to 100 kyr about 800kyr ago? Ice ages during past 600,000 yrs Last 5.5 Myr: ice ages started 2.7 Myr ago; occurred every 40 kyr until 800,000 yr & every 100 kyr since

Glacial cycles Observations &major problems: Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Glacial cycles Observations &major problems: 100 kyr, 41 kyr, mid-Pleistocene transition, CO2 changes Ingredients & basics: Energy balance, ice dynamics and Glenn’s law, ice streams, calving, temperature-precipitation feedback, isostatic adjustment, geothermal heating, ocean heat transport, Milankovitch … Mechanisms: “more theories than theoreticians”, but still some robust lessons: Phase locking to Milankovitch as a robust feature; need for a self-sustained oscillations that’s able to phase lock From curve fitting to falsifiable mechanisms Integrated insolation and 41 kyr oscillations CO2: intro to ocean biogeochemistry explaining glacial-interglacial CO2 variations. Final review

“Permanent El Nino” during the Pliocene, 2-5Myr Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate “Permanent El Nino” during the Pliocene, 2-5Myr [Wara et al 2005] [Medina Elizalde et al 2008]  The east-west temperature gradient in the equatorial Pacific did not exist during the Pliocene (2-5 Myr ago)

Warm Climates: Pliocene, 2-5 Myr Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Warm Climates: Pliocene, 2-5 Myr Observations & major problems: Permanent El Nino(?) Major warming of mid-latitude coastal upwelling sites Proxies, proxies, proxies. Mechanisms considered: Thermocline collapse (deepening) due to FW flux Tectonics: opening of central American seaway Tectonics: island movement to block equator in west Pacific Hurricanes and ocean mixing Atmospheric superrotation due to meridional eddy momentum fluxes by Rossby Waves Final review

Pliocene climate ideas Open central American seaway [Steph et al 2010] collapse equatorial thermocline w/ N. Pacific fresh water flux [Fedorov et al 2004/2006] Move Papua/ New Guinea; [Cane&Molnar 2001; Hurricanes/ ocean mixing [Emanuel 2002… Fedorov et al 2010/2013] Change easterlies via R.W. induced Superrotation

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Observations: very warm climate ~146-34 Myr ago: deep ocean ~15C; above freezing winter temperatures at 60N, Greenland & middle of Canada (now -30C); equator to pole Temp gradient ~ 25 (now >40). The mystery(?): Warm continental winter climate cannot be reproduced by GCMs even at very high CO2 levels Modern Model SST - Eocene Model SST Eocene Proxy SST Eocene Model SSS Present-day like geometry [Huber and Sloan, 2001]

Equable climate ideas Hurricanes and ocean mixing/ THC Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Equable climate ideas Hurricanes and ocean mixing/ THC Hurricanes and ocean mixing/ THC Convective tropospheric cloud feedback Polar stratospheric clouds (15-25km)

And thanks for a great semester… Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate The End Thanks Lauren! And thanks for a great semester… Final review

Let the fun begin…

Energy balance | El Nino | THC | DO & Heinrich | Glacial cycles | warm climate | Equable climate Let’s get started…

Climate dynamics & physical oceanography Eli Tziperman Museum building 456b 617-384 8381 eli@eps.harvard.edu The oceanography we need today…

Monsoon variability (~2 years) CNN, Aug 2000: Millions of people in 3 eastern states homeless by rains; 24 cm rain in a few days; highest in 50yr.

Monsoons: An intersection of science and societal issues Indian monsoons: what causes year to year variability of monsoon precipitation? Complex relations to El Niño, Tibetan snow, atmospheric dynamics, ocean circulation... Affects Indian agriculture, flooding, erosion, disease… Predictability?