Projections with CoupledClimate GCMs

Peter LemkeAlfred Wegener Institute

Helmholtz Center for Polar and Marine ResearchBremerhaven

Institute for Environmental PhysicsUniversity of Bremen

The Climate SystemHum

an I

mpa

ct

Interaction between climate components: exchange of heat, momentum, matter

ATMOSPHERE AND OCEAN MODELS

u⋅−∇=DtDρ

ρ1

1. Mass balance for water/air:

2. Mass balance for salt, water vapour

3. Energy balance

4. Momentum balance: Fguu++∇−×Ω−= p

DtD

ρ12

Basic variables:Temperature TSalinity, Humidity S, qPressure pVelocity u, v, w

Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere

Land surfaceLand surfaceLand surfaceLand surfaceLand surface

Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice

Sulphateaerosol

Sulphateaerosol

Sulphateaerosol

Non-sulphateaerosol

Non-sulphateaerosol

Carbon cycle Carbon cycle

Atmosphericchemistry

Ocean & sea-icemodel

Sulphurcycle model

Non-sulphateaerosols

Carboncycle model

Land carboncycle model

Ocean carboncycle model

Atmosphericchemistry

Atmosphericchemistry

Off-linemodeldevelopment

1975 1985 1992 1997

HADLEY CENTRE EARTH SYSTEM MODEL

The

Met

.Off

ice

Had

ley

Cen

tre

2001 200?

Figure 1.2

2007

19951990

2001

1990

1995

2001

2007

Sea ice model structure

Shth

+⋅−∇=∂∂ )(umass balance:

momentum balance: σττuku⋅∇+∇+×−= −+ Hmgmf

DtDm wa

Attribution Process

• other GHGs• aerosols• volcanic• solar• natural internal

Model

Fig SPM-3

SPM-1

Attribution

greenhouse gas emissions

no greenhouse gas emissions

Observed warming extremely unlikelynatural variability alone

GHG’s very likelycaused most of the observed warming since mid-century

Scenarios and projections

CO2 Emissions (Giga-Tonnes Carbon)

0

5

10

15

20

25

30

A2 A1B B1

200020202040206020802100

2

2.5

3

Projected CO2 Concentrations

ppmv

Scenarios of economic and technological development

Box TS.6 for further details

RCP8.5

RCP6.0

RCP4.5

RCP2.6

Representative Concentration Pathways (RCP)

RCP: CO2 ConcentrationsScenarios of economic and technological development

Global surface temperature change for the end of the 21st century is likely to exceed 1.5°C

relative to 1850 for all scenarios

(IPC

C 2

013,

Fig

. SPM

.7a)

Climate Projections

Global Surface Temperature

Arctic SeaIce Extentin Summer

Scenarios of future sea ice development

ACIA Report Walsh & Jakobsson, 2004

IPCC, B2

winter summer

Grand Challenge: Polar processes in

summer

Projections

Fig. SPM.7

Climate Projections

Projected patterns of precipitation changes

winter summer

wet winter dry summer

Figure SPM.8dMaps of CMIP5 multi-model mean results

All Figures © IPCC 2013

Global mean sea level will continue to rise during the 21st century

(IPC

C 2

013,

Fig

. SPM

.9)

Uncertainties in projections

Future climate change is a sum of:

• An externally forced response, due to changes in radiative forcingarising from human activity, variations in the sun and major volcaniceruptions

• Internal variability, e.g. the El Niño-Southern Oscillation (ENSO) and other patterns, and year-to-year and decade-to-decade fluctuations in winds, precipitation, temperature, …

Internal variability – an important source of climatevariability

The Climate SystemHum

an I

mpa

ct

Interaction between climate components: exchange of heat, momentum, matter

Global Mean Temperatures are rising

GISS Data

ΔT = 0,95°C

140 years ΔT = 1,0°C

Internal variability – an important source of climatevariability

Fig. 1.4

RCP8.5

Hatching: changes are “small” compared with internal variability

Stippling: changes are “large” compared with internal variability, and at least 90% of models agree on sign of change

How large is the projected change compared tointernal variability?

AR4 and AR5 projections are very similar whenaccounting for scenario differences

Fig. 12.41

Long term climate change andcumulative carbon

Warming will persist for centuries

• Zero CO2 emissions lead to near constant surface temperature.

• A large fraction of climatechange persists for manycenturies.

• Depending on the scenario, about 15-40% of the emitted carbon remains in the atmosphere for 1000 yrs.

Cumulative carbon determines warming

• Peak warming is approximately proportional to cumulative (total) emissions.

• Transient climate response to cumulative carbon emissions TCRE = Warming per 1000 PgC

Cumulative carbon determines warming

• Warming is largely independent ofthe emission profile. Only the totalmatters.

• More emissions early imply stronger reductions later.

• Any temperature target implies a maximum in cumulative CO2emissions. This is purely a physical and carbon cycle problem.

• Allocation over time is a economicand policy question.

• Overshooting the budget will overshoot the target.

Fig. 12.46

RCP2.6

Cumulative carbon determines warming

• Evidence from observations, and from simple to complex models for many scenarios.

• Near linear in all models, but the slope is uncertain.

• Any temperature target implies a maximum amount of carbon that can be emitted.

• Due to non CO2, RCP warming islarger than from CO2 only.

1%/yr CO2

RCP8.5

Fig. 12.45

Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions

(IPC

C 2

013,

Fig

. SPM

.10)

Cumulative carbon determines warmingRemaining Budget

(from Jan 2020)

1.5°C Warming:340 (500) Gt CO2

2.0°C Warming:1090 (1420) Gt CO2

Current annualemissions~ 37 Gt CO21.5°C: 9 (14) years2.0°C: 29 (38) years

IPCC SR15 (Fig. 2.3; Table 2.2; 2018)

Summary

• “Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions ofgreenhouse gas emissions.”

• Changes are projected throughout all climate components, in most cases exceeding natural variations by far. Changes in AR5 are similarto those in AR4 for similar scenarios.

• Every ton of CO2 causes about the same amount of warming, nomatter when and where it is emitted.

• To limit warming to likely less than 2oC as in RCP2.6 requires total emissions since preindustrial to be limited to less than about 790PgC. 515 PgC were emitted by 2011.

Foss

il fu

el C

O2

emis

sion

s [Pg

C/y]

Scenarios: IPCC Representative Concentration Pathways

Observation uncertainty band (± 1 standard deviation)

Data: CDIAC (preliminary for 2009, 2010)Figure: Raupach et al (in prep, Dec 2011)

Citation for data: Peters, G.P., Marland, G., Le Quéré, C., Boden, T., Canadell, J.C. and Michael R. Raupach (2011). Rapid growth in CO2 emissions after the 2008-2009 Global Financial Crisis. Nature Climate Change 1 (doi:10.1038/nclimate1332)

2100:ΔT ~ 4°C

CO2 Emissions (Billion Tonnes of Carbon/year)

... are near the worst scenario of the IPCC

Global emissions from fossil fuel and industry: 35.9 ± 1.8 GtCO2 in 2014, 60% over 1990 Projection for 2015: 35.7 ± 1.8 GtCO2, 59% over 1990

Estimates for 2012, 2013, 2014, and 2015 are preliminarySource: CDIAC; Le Quéré et al 2015; Global Carbon Budget 2015

Uncertainty is ±5% for one standard deviation

(IPCC “likely” range)

Emissions from fossil fuel use and industry

Global emissions from fossil fuel and industry: 36.2 ± 2 GtCO2 in 2016, 62% over 1990 Projection for 2017: 36.8 ± 2 GtCO2, 2.0% higher than 2016

Estimates for 2015 and 2016 are preliminary. Growth rate is adjusted for the leap year in 2016.Source: CDIAC; Le Quéré et al 2017; Global Carbon Budget 2017

Emissions from fossil fuel use and industry

Uncertainty is ±5% for one standard deviation

(IPCC “likely” range)

Global fossil CO2 emissions: 36.2 ± 2 GtCO2 in 2017, 63% over 1990 Projection for 2018: 37.1 ± 2 GtCO2, 2.7% higher than 2017 (range 1.8% to 3.7%)

Estimates for 2015, 2016 and 2017 are preliminary; 2018 is a projection based on partial data.Source: CDIAC; Le Quéré et al 2018; Global Carbon Budget 2018

Global Fossil CO2 Emissions

Uncertainty is ±5% for one standard deviation

(IPCC “likely” range)

Emissions from fossil fuel use and industry

Global fossil CO2 emissions: 36.4 ± 2 GtCO2 in 2019, 61% over 1990Projection for 2020: 34.1 ± 2 GtCO2, about 7% lower than 2019

Uncertainty is ±5% for one standard deviation

(IPCC “likely” range)

The 2020 projection is based on preliminary data and modelling, and is the median of the four studies.Source: CDIAC; Friedlingstein et al 2020; Global Carbon Budget 2020

Top emitters: Fossil CO2 Emissions

Emissions by country from 2000 to 2019, with the growth rates indicated for the more recent period of 2014 to 2019

Source: CDIAC; Jackson et al 2019; Friedlingstein et al 2020; Global Carbon Budget 2020

Emissions from coal, oil, gas, cement

Share of global fossil CO2 emissions in 2019: coal (39%), oil (33%), gas (21%), cement (4%), flaring (1%, not shown)Projection by fuel type is based on monthly data (GCP analysis)

Source: CDIAC; Friedlingstein et al 2020; Global Carbon Budget 2020

Total global emissions

Land-use change estimates from three bookkeeping models, using fire-based variability from 1997Source: CDIAC; Houghton and Nassikas 2017; Hansis et al 2015; Gasser et al 2020; van der Werf et al. 2017;

Friedlingstein et al 2020; Global Carbon Budget 2020

Total global emissions: 43.0 ± 3.3 GtCO2 in 2019, 56% over 1990Percentage land-use change: 39% in 1960, 14% averaged 2010–2019