Impactof regionally increasedCO2concentrations incoupled

climate simulations

TidoSemmler,FelixPithan,ThomasJung

Motivation

Everybody knows: Arctic sea ice has beenstrongly declining over the last 3 to 4 decadesMany studies have investigated the impact ofsuch Arctic sea ice decline on the Northern mid-latitudesBut which influence is stronger: from the Arctic to the Northern mid-latitudes orthe other direction?Novel approach: regionally prescribe 4*CO2 concentrations(recently applied by Stuecker et al., 2018)

• ECHAM 6.3 (from Max Planck Institute) coupled to FESOM 1.4 (AWI ocean model)

• Flexible mesh layout – examples:

Thetool:AWI-CM1.1(CMIP6version)

LR MR

Rackowetal.(2018)

HR

Experiments

control

4*CO2north of 70N4*CO2north ofJanuary ice edge

4*CO2north of 60N

4*CO2south of 60N

4*CO2globally

March

Responseinthe temperature profile4*CO2 north of 60 N for the first 30 years

Winter Spring

Summer Autumn

Warming restricted to near-surface,except for summer

Winter2mtemperature response (K)

4*CO2 north of 70 N for the first 30 years 4*CO2 north ice edge for the first 30 years

4*CO2 north of 60 N for the first 30 yearsNorth America and East Asiacooling without stratosphericwarming

Meridionalatm.energy transport (PW)

Difference to control simulation, first 30 years

Synoptic activity 500hPa(m)4*CO2 north of 60 N, DJF

First30years

Last120years

Less exchange Arctic– extra Arctic

Synoptic activity 500hPa(m)

4*CO2 south of 60 N, DJF

First30years

Redistribution ofincrease/decrease areas

Arctic sea ice volume inMarch

Strong extra-Arctic impact: Even withoutany Arcticforcing (browncurve) half ofthe sea ice ismelted in around 15 years throughatmosphericheat transport. Another sixthdue to oceanicheat transport.

Energy fluxes 70°NMeridional ocean transportsmall andmeridional atmospheretransport large. Howeveranomaliescomparable.

Ocean playsimportant role in redistribution ofenergy whenswitching on extra-Arcticforcing

First30years Surface Meridionalatmosphere

Meridionalocean

control -11.7 102.9 13.8

60N -10.5 98.6 14.6

60Ns -10.6 106.8 17.8

glob -9.7 101.1 18.8

Last30years Surface Meridionalatmosphere

Meridionalocean

control -13.0 101.6 15.2

60N -12.7 96.3 16.2

60Ns -14.8 103.9 20.0

glob -13.2 98.5 19.1

Responseinthe temperature profile4*CO2 south of 60 N for the first 30 years

Winter Spring

Summer Autumn

Arctic amplification without Arctic forcingexcept for summer!

Arctic Amplification Index(AAI)(60°NArctic temperature increase /globaltemperature increase)

Note: AAI = 1: no ArcticAmplification

High AAI forArctic forcingexperiments

60% of ArcticAmplificationdue tonorthwardenergytransport

Sinuosity index (Cattiaux etal.,2016,GRL)

SI = length of isohypse / length of 50°N latitude circleThe chosen isohypse is the area average of Z500 over 30 to 70°N

Sinuosity index NHfirst 30years

Smallersinuosity indexthroughout theyear as a resultof extra-Arcticforcing

Tendency toslightly larger sinuosity indexin winter andspring as a result of Arcticforcing but signal not robust

Sinuosity index NHlast30years

Smallersinuosity indexthroughout theyear as a resultof extra-Arcticforcing

Tendency toslightly larger sinuosity indexin winter andspring as a result of Arcticforcing but signal not robust

Conclusions

Method of regional decomposition of CO2 forcing works (see also Stuecker et al., 2018). Maybe an experiment design to be consideredfor PAMIP?Above 300 hPa cooling rather than warming (expected!) Generally despite strong CO2 forcing in the Arctic relatively littlehappens in the mid-latitudes, especially with increasing simulationlengthThe extra energy in the Arctic forcing experiments largely stays in theArcticIf forcing only outside the Arctic, the energy transport into the Arcticis strongly increased with an increasing role of the ocean over thesimulation timeTherefore, even without any Arctic forcing two thirds of the sea icemelt and Arctic Amplification exists: 60% of Arctic Amplification canbe explained by extra-Arctic forcing!

Winter500hPageopot response (m)

4*CO2 north of 70 N for the first 30 years 4*CO2 north ice edge for the first 30 years

4*CO2 north of 60 N for the first 30 years PNA pattern visible, but small anomalies!

WinterU300response (m/s)

4*CO2 north of 70 N for the first 30 years 4*CO2 north ice edge for the first 30 years

4*CO2 north of 60 N for the first 30 years Positive anomalies stretching fromGulf of Mexico / Florida to Southern Europe – surrounded by negative anomalies. But small anomalies!

Sinuosity index ATfirst 30years

Sinuosity index ATlast30years

Sinuosity index ASfirst 30years

Sinuosity index ASlast30years

Sinuosity index PAfirst 30years

Sinuosity index PAlast30years

Sinuosity index AMfirst 30years

Sinuosity index AMlast30years

Arctic sea ice concentration response (%)

4*CO2north of 60N,last30years,MAM

Arctic sea ice concentration response (%)

4*CO2north of 60N,last30years,SON

Yearly 2mtemperature response

4*CO2 north of 60 N for the last 30 years

Mean sea level pressure (hPa)4*CO2 north of 60 N, DJF

First30years

Last30years

500hPageopotentialheight (m)4*CO2 north of 60 N, DJF

First30years

Last30years

Synoptic activity 500hPa(m)4*CO2 glob, DJF

First30years

Last30years

Ocean mixed layer depth anomaly4*CO2 north of 60 N

First 30 years Last 30 years

1951-1980

Sea surface height (m)

4*CO2 north of 60 N, DJF

First30years

Last30years

Ocean temperature response (K)15m4*CO2 north of 60 N

First30years

Middle 30years

Last30years

Salinity response (psu)15m4*CO2 north of 60 N

First30years

Middle 30years

Last30years