DJF Warsaw Sept05

8/14/2019 DJF Warsaw Sept05

1/54

Oxford University

Predicting and Attributing Climate Change

Dave FrameDepartment of Physics, University of Oxford

Oxford University Centre for the Environment

[email protected]


2/54

Oxford University

Defining Climate

Climate is the statistics of the weather Global mean, annual mean surface temperature

East Pacific summer sea-surface temperatures Mean annual Indian Rainfall

Average July humidity in Toru

Return period of Florida hurricanes

Wide range of spatial and time scales involved Climate is what we expect; weather is what we get

Ed Lorenz


3/54

Oxford University

Climate responds due to:

Factors internalto the climate system: Variability in the atmosphere

Variability in the oceans Variability in the biosphere

Factors externalto the climate system: Rising levels of greenhouse gases

Volcanoes Fluctuations in solar output


4/54

Oxford University

Climate as a predictable system

Climate is to weather as the bank is to the roulette

wheel:

The statistics of the system are simpler than the

system itself

Easier to be right in the long run than in the short


5/54

Oxford University

Factors governing predictability

Initial conditions

are the state and trajectory of the climate system at thebeginning of the forecast

Boundary conditions

are the external factors that control the weather we

should expect on average

Necessary for predicting weather

Crucial in predicting climate


6/54

Oxford University

Predictive skill over time

Skill diminishes as natural anomalies in climate

wash out of the system (as the roulette wheel

relaxes back to its statistical norm)

Skill increases over time as the boundary conditions

start to drive the statistical norms (as the roulette

wheel gums up)


7/54

Oxford University

Sources of predictability

Time (yrs)

P r e

d i c

t i

v e

S k i l

l

Initial Conditionpredictability

Boundary ConditionPredictability


8/54

Oxford University

Boundary conditions and

global climate

Climate is determined by the boundary conditions ofthe atmosphere-ocean system:

solar irradiance (power output of the sun)

atmospheric composition (greenhouse gases, volcanic

activity, etc.)

positions of continents, ice-sheets etc.

If these change, climate is likely to change


9/54

Oxford University

Factors in the climate system

Kiehl and Trenberth, 1996


10/54

Oxford University

SUN

Sunlight

passesthrough the

atmosphere..

..and warms the earth.

..most escapes to outer space

and cools the earth...

Infra-red radiationis given off by the earth...

but some IR is

trapped by somegases in the air,

thus reducing the

cooling.

Source: Ellie Highwood


11/54

Oxford University

Energy in the climate system


12/54

Oxford University

Climate varies on geological timescales


13/54

Oxford University

Global Temperature last 1000 yr


14/54

Oxford University

In the light of new evidence and taking into account the remaining uncertainties,

most of the observed warming over the last 50 years is likely to have been dueto the increase in greenhouse gas concentrations

Source: IPCC Third Assessment Report, 2001


15/54

Oxford University

Model hierarchy

Physics constraints operate at all scales:

energy balance

energy transport

geostrophic balance

Moisture availiability

Cloud condensation principles


16/54

Oxford University

Model hierarchy

And we can usefully model the climate system at a

similarly wide range of scales

1. zero-dimensional energy balance models (EBMs);

2. one dimensional radiative-convective models (RCMs);

3. two-dimensional statistical-dynamical models (SDMs);

4. three-dimensional general circulation models (GCMs).


17/54

Oxford University

Energy Balance Models

TF

dt

Tdceff =

Treat the climate system as an energy balance

problem: what goes in must come out

Can write an equation that looks at temperatureresponse to forcing (changes in incoming or

outgoing radiation)


18/54

Oxford University

Energy Balance Models

TF

dt

Tdceff =

Treat the climate system as an energy balance

problem: what goes in must come out

Heat uptake

of the system

Climate

forcing

Temperature

response


19/54


20/54

Oxford University

Energy Balance Models - Ensembles

TF

dt

Tdceff =

Ideally, wed take an unbiased sample of all viable

climate models, but we cant do that

Best we can do is take this scatter-gun approach

Repeat with other models


21/54

Oxford University

General Circulation Model of the Atmosphere:

3 Equations of Motion

Equation of State

Energy EquationMass Conservation }

3D wind field

Temperature

PressureDensity

Convection scheme

Cloud scheme

Radiation scheme Sulphur cycle

Precipitation

Land surface and vegetation

Gravity wave drag scheme

The Model also includes:

Each of these equations is evaluated at each point in the model [96

longitudes by 73 latitudes by 19 vertical levels] every half hour

timestep


22/54

Oxford University

Climate modelling (1990)

General Circulation Models (GCMs)

Atmospheric GCMs

Ocean GCMs

Ocean only Model

Atmosphere only Model


23/54

Oxford University

Climate modelling (2000)

Coupled Ocean-Atmosphere GCMs

Ocean Model

Atmosphere Model


24/54

Oxford University

Climate modelling (2005?)

Coupled GCMs with biogeochemical cycles

Ocean Model

Atmospheric Model

CouplerCryosphere Model

Chemistry Model

Biosphere Model


25/54

Oxford University

GCM Performance

Modern Coupled GCMs

Perform well at continental scales Perform well at interannual -> climatological scales Perform less well at short time scales Perform less well at regional scales


26/54

Oxford University

Model simulation of recent climate

Natural forcings only(solar, volcanic etc. variability)

Anthropogenic forcings only(human-induced changes)


27/54

Oxford University

Model simulation of recent climate

Natural + Anthropogenic forcings

Natural forcings

Anthropogenic forcings


28/54

Oxford University

Solar forcing in models

Stott et al, 2001

Combined forcing, doubling solar response


29/54

Oxford University

Increasing greenhouse gases:

Increases the infrared opacity of the atmosphere.

Raises the mean altitude of air radiating to space.

Higher air is colder (by ~6K/km) and so emits less. Net radiation to space is reduced, by ~4W/m2 for a

doubling of CO2.

Climate system adjusts to restore balance.


30/54

Oxford University

Forcing Uncertainties


31/54

Oxford University

Warming rates in different models (Model

Spread)

Different

models yield

differentwarmings

under the same

scenarios


32/54

Oxford University

Net ranges under various scenarios


33/54

Oxford University

Developed Country Per capita Emissions far

Exceed Developing Country Per Capita Emissions


34/54

Ri k f l b l i fi t di 1 5K b


35/54

Oxford University

Risk of global warming first exceeding 1.5K by a

given date


36/54

Oxford University

Global model predictions


37/54

Oxford University

Zonal mean precipitation changes at time of CO2 doubling in CMIP-2

models


38/54

Oxford University

How uncertain are these model predictions?

Models depend on parameterisations of processes too small

to resolve.

Parameterisations represent the feedbacks between smaller

and larger scales.

Many prescribed parameters (e.g. ice fall speed in clouds)

are poorly constrained.


39/54

Oxford University

GCM resolution ~ 2.5 in lat,lon

Explicit representation of larger

scale features;Sub-grid scale processes need

to be parameterized

Arbitrarily small scales affect

arbitrarily large scales in finite

time (Lorenz 1969)

The Met Office


40/54

Oxford University

Uncertainty in climate forecasts


41/54

R i l t t d i it ti


42/54

Oxford University

Standard model version

Low sensitivity model

High sensitivity model

Regional responses: temperature and precipitation


43/54

Oxford University

Uncertainty in climate forecasts

Combining physical uncertainty with economic


44/54

Oxford University

Temperature Change (Degrees C) 2000-2100

0 1 2 3 4 5 6 7

Proba

bilityDensity

0.0

0.1

0.2

0.3

0.4

0.5

Median: 2.3

Lower 95%: 0.9

Upper 95%: 5.3

Combining physical uncertainty with economic

uncertainty: the Integrated Assessment problem

Source: Webster et al, 2001

El t f S t i bl D l t


45/54

Oxford University

Elements of Sustainable Development

Courtesy of The World Bank

S


46/54

Oxford University

Carbon

Trading

JI

More

Renewables

More

GEF

Clean

Technology

Clean

Fuel

Economic

InstrumentsEnvironmental

Standards

Regional

Agreements

Sector

Reform

Energy

EfficiencyRural

Energy

Internalizing

Global Externalities

(supporting the post-

Kyoto process)

Local/Regional

PollutionAbatement

(to be

strengthened)

Win-Win

(in place)

World Bank Strategy

Regional Behaviour European Precipitation


47/54

Oxford University

Mediterranean Basin Northern Europe

Winter

Winter

Summer

Summer

Annual Annual

Unpublished analysis from climateprediction.net: Source: David Stainforth


48/54

Oxford University

Record hot events are more likely in a generally warmer world

Summer 2003 temperatures relative to 2000 2004


49/54

Oxford University

Summer 2003 temperatures relative to 2000-2004

From NASAsMODIS - Moderate

Resolution Imaging

Spectrometer,

courtesy of Reto

Stckli, ETHZ


50/54

Oxford University

Excess mortality rates in early August 2003 indicate 22,000 - 35,000 heat-related deaths

Daily mortality in Baden-Wrttemberg


51/54

Oxford University

Was the hot summer of 2003 due to climate change?

Anthropogenic emissions of greenhouse gases have doubled the risk of a

summer like 2003

By 2050, it could be that hot every other summer


52/54

Standard Visualisation Package


53/54

Oxford University

http://www.climateprediction.net


54/54

Oxford University

Since September 2003,

100,000 participants in 142 countries havecompleted 100,000 45 -year GCM runs

computed 3 million model years

donated 8,000 years of computing time

Documents

DJF Warsaw Sept05