Physical Science Basis of Climate Change: IPCC 2007 Jagadish Shukla Center of Ocean-Land- Atmosphere...

Physical Science Basis of Climate Change: IPCC 2007

Jagadish ShuklaJagadish Shukla

Center of Ocean-Land-Atmosphere studies

Apr 29, 2008

CLIM 759: Topics in Climate Dynamics GEOG 670: Applied Climatology

Chapter 9: Understanding and Attributing

Climate Change

• CO2 emissions have grown by 80% between 1970 and 2004.CO2 emissions have grown by 80% between 1970 and 2004.(2005: 379 ppm; All GHG: 455 ppm (CO2 equivalent); Primary reason: fossil fuel use and land-use change)

• Rate of increase of CORate of increase of CO22, CH, CH44, N, N22O was the largest in 10,000 years.O was the largest in 10,000 years.

• Aerosols have partly offset the warming by COAerosols have partly offset the warming by CO22..

• Global mean surface temp. increase (linear trend) 0.76Global mean surface temp. increase (linear trend) 0.76ooC in 100 C in 100 years (1906-2005).years (1906-2005).

• Eleven of the past twelve years are the warmest on record.Eleven of the past twelve years are the warmest on record.

• In the past 500 years, the warmest 50 years were 1951-2000.In the past 500 years, the warmest 50 years were 1951-2000.

The Knowns (Observed)The Knowns (Observed)


• Sea level has risen 1.8 mm/yr since 1961; 3.1 mm/yr since 1993.Sea level has risen 1.8 mm/yr since 1961; 3.1 mm/yr since 1993.

• Arctic sea ice extent reduced by 2.7% per decade since 1978.Arctic sea ice extent reduced by 2.7% per decade since 1978.(The summer minimum on record; 2007)

• Enhanced run-off and earlier spring peak discharge in many Enhanced run-off and earlier spring peak discharge in many glaciers and snow-fed rivers.glaciers and snow-fed rivers.

• Extreme hot nights have increased ; frost days have decreased.Extreme hot nights have increased ; frost days have decreased.

• Earlier timing of spring events (blooms) on land.Earlier timing of spring events (blooms) on land.

• Poleward and upward shifts in plant and animal ranges.Poleward and upward shifts in plant and animal ranges.

• Changes in algal, plankton, and fish abundances (~Temp.).Changes in algal, plankton, and fish abundances (~Temp.).

• Increase in the acidity of oceans.Increase in the acidity of oceans.

The Knowns (Observed)The Knowns (Observed)


LAST CENTURY OR SO …LAST CENTURY OR SO …


What’s Happening in the Upper Atmosphere?What’s Happening in the Upper Atmosphere?


FAQ 9.1, Figure 1. Summer temperatures in Switzerland from 1864 to 2003 are, on average, about 17°C, as shown by the green curve. During the extremely hot summer of 2003, average temperatures exceeded 22°C, as indicated by the red bar (a vertical line is shown for each year in the 137-year record). The fitted Gaussian distribution is indicated in green. The years 1909, 1947 and 2003 are labelled because they represent extreme years in the record. The values in the lower left corner indicate the standard deviation (σ) and the 2003 anomaly normalised by the 1864 to 2000 standard deviation (T’/σ). From Schär et al. (2004).

Can Individual Extreme EventsCan Individual Extreme Eventsbe Explained by Greenhouse Warming?be Explained by Greenhouse Warming?

Changes in Greenhouse GasesChanges in Greenhouse Gases


From Ice Age to Modern DataFrom Ice Age to Modern Data

Recent analyses of satellite measurements do not indicate a long-term trend in solar irradiance (the amount of energy received by the sun), Frohlich and Lean (2005)


Solar IrrandianceSolar Irrandiance

• Limits of deterministic predictionLimits of deterministic prediction(attribution of an event (Katrina) is not possible)

• No model can explain the past 50 year observed global warming No model can explain the past 50 year observed global warming without increase in the green house gases (GHG).without increase in the green house gases (GHG).

• Sun and volcanoes would have produced cooling.Sun and volcanoes would have produced cooling.

• There is no mechanism known to scientists that can explain the There is no mechanism known to scientists that can explain the global structure of warming in the A, O, L without GHG.global structure of warming in the A, O, L without GHG.

• Warming and sea level rise would continue for centuries, even if Warming and sea level rise would continue for centuries, even if GHG were stabilized. GHG were stabilized.

• Increase in the frequency of heat waves and heavy precipitation.Increase in the frequency of heat waves and heavy precipitation.

• Entire disappearance of arctic late summer sea ice ( ~ 2100 ).Entire disappearance of arctic late summer sea ice ( ~ 2100 ).

The Knowns (Models)The Knowns (Models)


• Equations of motions and laws of thermodynamics to predict rate of change of:

T, P, V, q, etc. (A, O, L, CO2, etc.)

• 10 Million Equations: 100,000 Points × 100 Levels × 10 Variables

• With Time Steps of: ~ 10 Minutes

• Use Supercomputers

What is a Climate Model?What is a Climate Model?

Global mean, volume mean ocean Global mean, volume mean ocean temperaturetemperatureCourtesy of Tom Delworth (GFDL)

GFDL Model Simulations

Report of the WCRP Workshop (163 participants, 29 nations)

Thank you!

Courtesy of John ChurchCSIRO Marine & Atmospheric Research

Hobart, Tasmania, Australia

Climate models without volcanic ForcingClimate models without volcanic Forcing

Domingues et al. 2008

Climate models withClimate models with volcanic Forcingvolcanic Forcing

ThSL: Thermosteric sea level change(density changes induced by temperature change)

(0-700 m)

1. Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR)

• Definitions

• Model ECS and TCR—the role of feedbacks

2. Detection and Attribution

• Detection and Attribution of What?

• Modeling with and without anthropogenic forcing

3. Understanding?

Understanding and Attributing Climate ChangeUnderstanding and Attributing Climate Change


Definition: The ECS is the full equilibrium surface temperature response to a doubling of CO2

Definition: The TCR is the surface temperature response at CO2 doubling for a 1%/yr increase of CO2 (i.e. at year 70)

a. ECS and TCR are basically model concepts

b. TCR < ECS

c. ECS is a measure of the feedbacks in the system:

Recall:

Equilibrium Climate Sensitivity (ECS) and Equilibrium Climate Sensitivity (ECS) and Transient Climate Response (TCR)Transient Climate Response (TCR)


Solar Radiation Energy Input (SRE) = Outgoing Terrestrial Radiation Energy (TRE)

π r2 So (1-α) = 4πr2 σTe4

[So (1-α)] / 4 = σ Te4 = S

Te = (S/ σ)1/4 = 255oK

Actual surface Ts = 288oK (15oC)

Te is ~ temperature at 6 Km (lapse rate ~ 5.5 oC/Km)

r = radius of Earth πr2 = area of ‘Earth disc’α = albedo (0.3)Te = effective radiating temperature of Earth So = Solar irradiance = 1367 Wm-2

S = mean flux of absorbed solar radiation per unit area = 239 Wm-2

σ = Stefan-Boltzman Constant (5.67x10-8 Wm-2K-4 )

Simple Climate Model (1)Simple Climate Model (1)


[So (1-α)] / 4 = σ Te4 = S

dTe / Te = ¼ dSo/So = ¼ dS/S

dTe/dSo = Te/4So (Assuming α is constant)

If So increase by a small percentage β, Te will increase by a percentage ¼ β

(If So increase by 2 percent ; Te will increase by ½ percent)

If there were no feedback in the system, surface temperature (TS) will increase by same amount as Te. But that is not the case because of feedbacks.





Define ΔTo as change in temperature without feedbacks, ΔTs is the actual change in Earth surface temperature.

Define a feedback factor, f such that f is equal to : ΔTs / ΔTo

ΔTs= fΔTo = ΔTo+ ΔTfeedabck

Divide by ΔTs ; ΔTs/ ΔTs = ΔTo/ΔTs + ΔTfeedabck/ ΔTs

Define gain g is equal to : ΔTfeedabck/ ΔTs = g (gain)

1=1/f +g ; f = [1-g] -1

But suppose there are many feedbacks, then have gi = ΔTfeedabck i / ΔTs ; i=1,2,3,…

g=g1+g2+g3+….

ΔTs = fΔTo ; f = (1- Σ gi) -1 = [1-(g1+g2+g3+…)]-1



Models show: g1 (water vapor / lapse rate) = 0.4

g2 (snow/ice albedo) = 0.1

ΔTo is change in temperature without feedbacks.

ΔTo = 1.2 oC (for doubling of CO2 Radiative forcing of 4 W/m2 and No feedback)

For climate models: g = 0.6 ; f = (1-0.6)-1 = (0.4)-1 = 2.5

So, ΔTs = 2.5 (ΔTo) = 2.5 (1.2) = 3oC

(Please note aerosols are forcing not feedback.)

Quasi-linear Dependence between Outgoing Longwave Quasi-linear Dependence between Outgoing Longwave Radiation and Surface Temperature for Seasonal CycleRadiation and Surface Temperature for Seasonal Cycle


Lecture by P. Morel, at European Geoscience Union in Vienne, Apr. 2008

Climate sensitivity : Ratio between mean surface warming (ΔToC) and corresponding increment (Δ F Watt/m2) in OLR at tropopause.

Despite a factor 2 difference in seasonal temperature ranges for NH and SH, climate sensitivity is nearly equal (0.56 oK/Wm-2).

λ (no feedback) = 0.3 oK/Wm-2

λ (GCM, fdbk) = 0.75 oK/Wm-2

Equilibrium Climate Sensitivity (ECS) for Equilibrium Climate Sensitivity (ECS) for Anthropogenic Climate ChangeAnthropogenic Climate Change


ECS: The equilibrium change in the annual mean global surface temperature following doubling of the atmospheric equivalent carbon dioxide (CO2) concentration.

ECS for TAR: 1.5oC to 4.5oC

ECS for AR4: 3oC

• Based on observational constraint: the most likely value between 2°C and 3°C.

• Based on AR4 AOGCMs: the most likely value between 2.1°C to 4.4°C, mean value 3.3°C.

• Based on observations and models: in the range of 2°C to 4.5°C, with a most likely value of about 3°C.

d. Climate model sensitivity is usually gotten by coupling to a mixed layer model with mean heat transport specified as a Q-flux and then doubling CO2 [initial condition matters].

This assumes that the ocean heat transport doesn’t change.

The TCR scales with the ECS-depends on ocean heat uptake.



Figure 10.25. (a) TCR versus equilibrium climate sensitivity for all AOGCMs (red), EMICs (blue), a perturbed physics ensemble of the UKMO-HadCM3 AOGCM (green; an updated ensemble based on M. Collins et al., 2006) and from a large ensemble of the Bern2.5D EMIC (Knutti et al., 2005) using different ocean vertical diffusivities and mixing parametrizations (grey lines).

There are uncertainties in observations and RF and, even if known, ECS still depends on models.

The models used are usually simpler models (EBMs or EMICs).



Figure 9.21. Probability distributions of TCR (expressed as warming at the time of CO2 doubling), as constrained by observed 20th-century temperature change, for the HadCM3 (Table 8.1, red), PCM (Table 8.1, green) and GFDL R30 (Delworth et al., 2002, blue) models. The average of the PDFs derived from each model is shown in turquoise. Coloured circles show each model’s TCR. (After Stott et al., 2006c).


Global Global and Continental Temperature and Continental Temperature ChangeChange

Comparison of observed continental- and global-scale changes in surface temperature with results simulated by climate models using natural and anthropogenic forcings. Decadal averages of observations are shown for he period 1906-2005 (black line) plotted against the centre of the decade and relative to the corresponding average for 1901-1950. Lines are dashed where spatial coverage is less than 50 %. Blue shaded bands show the 5-95% range for 19 simulates form 5 climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5-95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings.


Mean of 15 Models Surface Air Temperature Mean of 15 Models Surface Air Temperature DifferenceDifference(Sresa1b YR 71-100) minus (20c3m 1969-98), Global Average = (Sresa1b YR 71-100) minus (20c3m 1969-98), Global Average =

2.612.61

Courtesy of UCAR

1.0º C



Mean of 15 Models Surface Air Temperature Mean of 15 Models Surface Air Temperature DifferenceDifference(Sresa1b YR 71-100) minus (20c3m 1969-98), Global Average = (Sresa1b YR 71-100) minus (20c3m 1969-98), Global Average =

2.612.61


Climate Model Fidelity and Projections of Climate ChangeJ. Shukla, T. DelSole, M. Fennessy, J. Kinter and D. Paolino

Geophys. Research Letters, 33, doi10.1029/2005GL025579, 2006

THANK YOU!

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Physical Science Basis of Climate Change: IPCC 2007 Jagadish Shukla Center of Ocean-Land- Atmosphere...

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