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Ch. 10 Global Climate Projections. Li Jian Erik Swenson Youkyoung Jang. Uncertainty in Global Climate Change Projections. Equilibrium Climate Sensitivity Response after equilibrium is reached Indication of model feedbacks Transient Climate Response (TCR) 1% yr -1 increase for 100 yrs

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Ch 10 global climate projections

Ch. 10 Global Climate Projections

Li Jian

Erik Swenson

Youkyoung Jang

Globally averaged t sfc air after co 2 doubling

Equilibrium Climate Sensitivity

Response after equilibrium is reached

Indication of model feedbacks

Transient Climate Response (TCR)

1% yr-1 increase for 100 yrs

Result at time of doubling

TCR < Equilibrium

Ocean heat uptake causes lag in warming

Globally averaged Tsfc (air) after CO2 doubling

Fig. 10.25a

Pdfs from constraints
PDFs from Constraints

  • likely range: TAR 1.50C to 4.50C

    AR4 2.00C to 4.50C

  • PDfs more


Box 10.2

Uncertainty from internal variability
Uncertainty from Internal Variability

  • Initial value problem

  • Chaos due to nonlinearity of dynamical system

  • Considered by taking ensembles within each model

Uncertainty with emissions
Uncertainty with Emissions

  • Dependent on important socioeconomic drivers, technological development, and political decisions

  • Not addressed in AR4

  • 6 SRES scenarios span different emission futures

    • Assume no mitigation, but wide variation

    • considered equally probable

  • Further uncertainty quantified after assuming a particular scenario will occur

Uncertainty with physical processes
Uncertainty with Physical Processes

  • Parameterization schemes

    • Ocean heat uptake / vertical mixing

    • Aerosol forcing

    • Clouds / precipitation

    • Multi-model ensembles attempt to sample all options

    • Individual studies play around with parameters

  • Water vapor feedback

    • Influences CH4 projections

  • Carbon cycle feedback (tune EMIC to AOGCM)




Fig. 10.26




Fig. 10.26

Time dependence

Projections have more agreement first few decades (models & scenarios)

Over a longer time scale feedbacks become more important  more uncertainty

Time Dependence

Fig. 10.28

Emissions commitment

Atmospheric concentration depends on sources and sinks scenarios)

CO2 removal processes have multiple time scales (undefined lifetime)

Emissions Commitment


120 yrs


12 yrs

FAQ 10.3, Fig. 1

Projected Changes scenarios)

  • Multi-model data set

  • 1% increase

  • equilibrium 2 x

  • 2 x , 4 x atmospheric in the 1%

  • - change of emission in models --> radiative forcing change

  • --> climate response (temperature, precipitation, atmospheric

  • circulation)

Radiative forcing Change during 2000 ~ 2100 scenarios)

Long wave forcing

Short wave forcing

Instantaneous radiative forcing and flux change scenarios)

in vertical

Doubling in atmosphere --> specific humidity increase


Projected Change: Physical Climate System scenarios)

A2(high), A1B(medium), B1(low) : prescribed concentrations and

resulting forcing relative to the SRES range

Projected Change: Physical Climate System scenarios)



Patterns of Change in 21st century: scenarios)

zonal mean (2080~2099 relative to 1980~1999)

Patterns of Change scenarios):

mean change for 2080~2099 from 1980~1999

Patterns of Change scenarios)

: cloud fraction (important link to humidity and precipitation)



Relative to


Patterns of Change: Precipitation and surface water scenarios)

Annual mean, A1B: 2080~2099 relative to 1980~1999

Changes in Meridional Overturning circulation scenarios)

In high latitude: temperature and precipitation increase

--> less dense water

--> stable ocean

--> inhibit convective process

Changes in Atlantic meridional overturning circulation scenarios)

1850~1999: 20th century climate in Coupled Model(20C3M)

1999~2100: SRES A1B emission scenario

~2200: forcing held constant at the values of year 2100

3 6 weather and climate extremes
3.6 weather and climate extremes scenarios)

  • Precipitation extreme

    • Increased risk of drought (drought areas increase from 1% to 30% in A2)

    • Increased chance of intense precipitation and flooding

  • Temperature extreme

    • Raise probability of extreme warm seasons

    • Decline the frequency of cold air outbreaks in NH winter

  • Hurricanes and storms

    • Coarse resolution models :: more intense precipitation

    • High resolution models :: increase in peak wind speed and precipitation intensity, might globally decrease frequency

    • Polarward shift of storm track

Figure 10 18
Figure 10.18 scenarios)

4 1 carbon cycle and vegetation feedback
4.1 carbon cycle and vegetation feedback scenarios)

  • Coupled climate-carbon cycle model intercomparison project (C4MIP, 11 models)

    • Results: Climate change will reduce the efficiency of land and ocean to absorb CO2

  • Positive feedback

    • CO2>Warm>Decrease absorption>CO2>warm…..

  • Two extreme models

    • CO2 concentration +20ppm +220ppm

    • Radiative forcing +0.1 W/m-2 +1.3W/m-2

    • Temperature +0.1 oC +1.5 oC

Figure 10 20

1020 ppm scenarios)


emission scenario

Figure 10.20

836 ppm

730 ppm

C4MIP :: 2.4~5.6 oC

AR4 :: 2.6~ 4.1 oC

Goal scenarios)

Simulation w/o coupled climate carbon cycle

Simulation w/ coupled climate carbon cycle

Reduce more CO2 emission

4 2 ocean acidification
4.2 Ocean acidification scenarios)

  • Increasing CO2 lower ocean pH

  • By 2100, ocean pH is projected to decrease 0.3~0.4 unit. Affect ecosystem. (muti-model)

  • Deep ocean chemistry structure

Figure 10.23. scenarios)Multi-model median for projected levels of saturation (%) with respect to aragonite, a meta-stable form of calcium carbonate, over the 21st century from the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP-2) models (adapted from Orr et al., 2005). Calcium carbonate dissolves at levels below 100%. Surface maps (left) and combined Pacific/Atlantic zonal mean sections (right) are given for scenario IS92a as averages over three time periods: 2011 to 2030 (top), 2045 to 2065 (middle) and 2080 to 2099 (bottom). Atmospheric CO2 concentrations for these three periods average 440, 570 and 730 ppm, respectively. Latitude-depth sections start in the North Pacific (at the left border), extend to the Southern Ocean Pacific section and return through the Southern Ocean Atlantic section to the North Atlantic (right border). At 100%, waters are saturated (solid black line - the aragonite saturation horizon); values larger than 100% indicate super-saturation; values lower than 100% indicate undersaturation. The observation-based (Global Ocean Data Analysis Project; GLODAP) 1994 saturation horizon (solid white line) is also shown to illustrate the projected changes in the saturation horizon compared to the present.

Figure 10.24. scenarios)Changes in global average surface pH and saturation state with respect to aragonite in the Southern Ocean under various SRES scenarios. Time series of (a) atmospheric CO2 for the six illustrative SRES scenarios, (b) projected global average surface pH and (c) projected average saturation state in the Southern Ocean from the BERN2.5D EMIC (Plattner et al., 2001). The results for the SRES scenarios A1T and A2 are similar to those for the non-SRES scenarios S650 and IS92a, respectively. Modified from Orr et al. (2005).

4 3 future evolution of ozone
4.3 Future evolution of ozone scenarios)

  • Coupled chemistry-climate models

  • Trend in upper-stratospheric ozone changes sign between 2000 and 2005

    • Anthropogenic activity,

    • Climate conditions,

    • Stratosphere-troposphere exchange

  • Troposphere ozone increase throughout 21st century

    • +20~25% from 2015~2050 (Grewe et al. 2001)

    • +40~60% at 2100 (Stevenson et al. 2001)

  • Ozone increases are largest in the tropics and subtropics

4 4 aerosol species
4.4 Aerosol species scenarios)

  • Of 23 models for IPCC AR4

    • 13 include aerosol species

      • 7 have non-sulphate species interact with other physics

        • 2 models treat Nitrates

  • Black and organic carbon :: highly simplified bulk parametrizations

  • Interaction of soil dust is under active investigation

  • Uncertainty also come from unpredictable natural forcing such as volcanic eruptions and solar variability

6 1 sea level rise due to thermal expansion
6.1 sea level rise due to thermal expansion scenarios)

  • Calculated from ocean temp.

  • 17 models results available

Figure 10.31. scenarios)Projected global average sea level rise (m) due to thermal expansion during the 21st century relative to 1980 to 1999 under SRES scenarios A1B, A2 and B1. See Table 8.1 for model descriptions.

6 2 local change due to density and dynamics
6.2 local change due to density and dynamics scenarios)

  • Dynamic topography <-- local T & S & circulation

  • 16 models (A1B)

  • Spatial patterns are different among models

Figure 10.32. scenarios)Local sea level change (m) due to ocean density and circulation change relative to the global average (i.e., positive values indicate greater local sea level change than global) during the 21st century, calculated as the difference between averages for 2080 to 2099 and 1980 to 1999, as an ensemble mean over 16 AOGCMs forced with the SRES A1B scenario. Stippling denotes regions where the magnitude of the multi-model ensemble mean divided by the multi-model standard deviation exceeds 1.0.

6 3 glaciers and ice caps
6.3 Glaciers and ice caps scenarios)

  • Mass balance sensitivity to T and P

    • Under A1B A2 and B1 -> 0.61mm/yr or 0.49mm/yr

    • Required increase P 20~50%/oC 29~41%/oC

  • Dynamic response and feedback

    • Volume lost-- area decline -- ablation decrease

  • Glacier and IC on Greenland and Antarctic

    • 10~20% sea level rise contribution of G&IC in future decades

6 4 ice sheet
6.4 Ice sheet scenarios)

  • Surface mass balance (SMB)

    • Increase in accumulation

    • Antarctic SMB changes will contribute negatively to sea level

    • Greenland SMB represents a net positive contribution to sea level

Long term commitment

EMICs scenarios)

A1B before 2100

Constant composition 2100-3000

Tsfc stabilizes relatively quickly

Sea level continues to rise

MOC shutdown?!

Long Term Commitment

Fig. 10.34

Long term commitment1

Path to CO scenarios)2 stabilization at 750 ppm before 2100

Zero emissions 2100-3000

Model dependence

Notice carbon redistribution

Long Term Commitment

Fig. 10.35

Greenland ice sheet
Greenland Ice Sheet scenarios)

  • Threshold for surface mass balance (SMB) of Greenland ice is 3.20 C - 6.20 C warming

    • Global average of 1.90 C - 4.60 C

    • Likely to be reached with A1B to 2100

  • Under constant 4*CO2, half of ice gone in ~1000 yrs

  • With less ice, Greenland’s climate is warmer (albedo feedback)  IRREVERSIBLE?

Fig. 10.38

Antarctic ice sheet scenarios)

Antarctic Ice Sheet

  • Growing as a whole

  • Concern is West Antarctic ice

    shelves breaking off

    • Base melt rate  water T near base

    • Entire sheet  5m sea level rise!

  • “We are not able to relate this quantitatively to global warming with any confidence …”

  • May explain some part of sea level rise for last interglacial (4-6m)