CCSM PaleoClimate Working Group Transient Mid-Holocene Simulation Caspar Ammann Bette Otto-Bliesner Esther Brady Carrie Morrill Fortunat Joos Raimond Mueschler Sam Levis Bob Tomas Noah Diffenbaugh Zhengyu Liu Matthew Huber Bruce Briegleb Goal Simulating mid-Holocene natural climate variability and potential abrupt climate change Model CCSM3, fully coupled T31x3 with dynamic vegetation Forcing Variable orbital, solar irradiance, ghg and explosive volcanoes Initialization Fixed forcing 6000 BP spinup with dynamic vegetation (300 yr)

Years (~ 5920 BP) Compared to Pre-Industrial Wm -2 North Pole -1.0 Wm -2 Equator Years (~ 4410 BP) Compared to Pre-Industrial +3.6 Wm -2 North Pole -0.8 Wm -2 Equator

Transient Mid-Holocene Temperature Trends Global Mean Surface Temperature Ocean Mean Temperature 6000 BP4350 BP

Years (~5920 BP) Years (~4410 BP) JJA Ts Difference with PI JJA Precipitation Difference with PI

North African Grasses and Boreal Forests have small downward trends in percent concentrations North African Monsoon, 10 to 30 latitudeBoreal, 50 to 90 latitude 6000 BP4200 BP 6000 BP4200 BP

JAS years (~5000 BP) minus (~5800 BP) Precip (color, 0.2 mm/day) SLP (contours, 0.2 mb) 1000 mb Wind (vectors, 1 m/sec reference) mm / day

Years 5900 BP4400 BP

Pre-Industrial Dynamic Vegetation Transient Mid-Holocene 6000 BPPresent

Transient Mid-Holocene Simulation Preliminary Results after 1650 years Global cooling C Stabilization of ocean temperature Southward shift in African-Asian monsoons Some southward shift in boreal forests and North African grasses Current Plan Run forward to present day At ~10 yrs / day, might finish late summer 2007 Encourage Analysis Some interesting features noticed already Will any abrupt changes occur? Stay tuned Selected data analysis available online at: Data available on NCAR Mass Store /CCSM/paleo/b30.108

Transient Holocene Simulation Players Carrie Morrill, Caspar Ammann, Bette Otto-Bliesner, Fortunat Joos, Raimond Mueschler, Sam Levis, Bob Tomas, Noah Diffenbaugh, Zhengyu Liu, Matthew Huber, Bruce Briegleb Vision Many paleoclimate proxy records show abrupt shifts in the mid-Holocene. The Transient Holocene simulation allows us to address: (1) Are there any abrupt changes simulated by CCSM3 (either regional, hemispheric or global)? (2) If yes, how are these transitions similar/different from those observed in paleoclimate records (i.e. location, speed, direction of climate change)? (3) If no, what are the limitations of the model and its forcings? What else might need to be changed for abrupt changes to occur? Model CCSM3, T31 x 3 Includes dynamic vegetation Initialized from 6 kyr ago spinup with dynamic vegetation, 300 years long

Transient Holocene Simulation (cont) Forcings Orbital: Parameters updated every four years. Solar: Solar constant from fit to solar modulation estimated from 14 C/ 10 Be ice core data, using satellite observations at end of record. Peak to peak range 0.12% of mean; minimal trends. GHG: CO 2, CH 4 and N 2 O using smooth fits to ice core data. Volcanic: Statistical occurance from 4050 BC to 850 AD, historical after 850 AD. Maximum monthly tropical volcanic mass equals Tambora 1815; maximum extratropical equals Laki History Files Monthly means: cam, pop, clm, csim. Daily means: 850, 300 hPa, sea level pressure; surface temperature and precipitation.

Transient Holocene Simulation (cont) Current Status Out 800+ years (i.e. from 4050 BC to 3250 BC) Progressing approximately 10 years / day Preliminary Results Noticeable short term impact of volcanoes. Slight global cooling trend (-0.1 to -0.2 C) Southward shift in subtropical Monsoon and vegetation associated with regional cooling, presumably due to changes in orbital forcing. Noticeable modulation of C3 grasses in African Monsoon, presumably due to drought cycles. Southward shift in boreal forests, also presumably due to changes in orbital forcing.

Years Years Orbital forcing has small changes over several hundred years

Greenhouse gases have small and very smooth changes

Summary of Forcings Orbital ~ 0.5 W m -2 / century mid to high latitudes; long term secular trend Solar ~ 0.29 W m -2 peak-to-peak over ~2 centuries; no secular trend GHG ~ W m -2 / century CO 2, 4050 BC to ~1000 AD ~ W m -2 / century CH 4, 4050 BC to ~ 1500 AD ~ W m -2 / century N 2 O, 4050 BC to ~ 1000 BC Volcanic 0 down to -10 W m -2, but short lived (a few years). Estimated long term (i.e. several hundred years) mean forcing ~ -0.3 W m -2

Top of model fluxes show volcanic forcings Global surface temperature shows small cooling trend High northern latitude snow depth shows slight upward trend

Years Years JJA Solar Insolation JJA Ts

Years Years JJA Ts JJA Precipitation

African Grasses and Boreal Forests have small downward trends in concentrations African Monsoon, 10 to 30 latitudeBoreal, 50 to 90 latitude

Transient Holocene Simulation Preliminary Results Noticeable short term impact of volcanoes. Slight global cooling trend (-0.1 to -0.2 C) Southward shift in subtropical Monsoon and vegetation associated with regional cooling, presumably due to changes in orbital forcing. Noticeable modulation of C3 grasses in African Monsoon, presumably due to drought cycles. Southward shift in boreal forests, also presumably due to changes in orbital forcing.

Transient Holocene Simulation Current Plan Run out 2400 years, or from 4050 BC to 1650 BC At approximately 10 years / day, should finish August 2006 Encourage Analysis Some interesting features noticed already Will any abrupt changes occur? Stay tuned Selected data analysis available online at: and updated every few days Data available on NCAR Mass Store /CCSM/paleo/b Monthly and selected daily data available Future? Forcing files continuous up to 2000 AD