Why Climate Models are the Greatest Feat of Modern Science

Julia Slingo, Met Office

17 fatalities (6 in UK)

London transport shut down during peak of storm (130 Heathrow flights cancelled)

850,000 homes lost power

Dungeness B Nuclear Power station shut down

Landslip and 100+ trees uprooted over rail lines resulting in long delays

Ferries badly affected; Port of Dover closed 06:00 to 09:30

28th October 2013:St Jude Storm

© Crown copyright Met Office

5 day forecast – before the storm even existed!

The same model which produced this forecast is used to simulate the atmosphere in the climate model

‘Riding on the back’ of 40 years of improvements in forecast skill

Day 1

Day 2 Day 3

Day 4

Day 5

‘1 Day per Decade’

Error in Mean Sea Level Pressure (mb) for the Euro-Atlantic Region

Tomorrow’s weather is the same as today’s!

Content DividerHow does the climate system work?

Global Mean Climate System

From Trenberth et al., 2009

Role of atmosphere and ocean dynamics in energy transports

Total radiative heating (Wm-2)

Poleward transports (PetaWatts) required to balance radiative heating/cooling

Total

Atmosphere

Oceans

Atmospheric Energy Transport

Energy transports achieved through planetary circulations, waves and weather systems

• Fluid on a rotating sphere – conservation of angular momentum

• Heated differentially between the equator and poles

• Effects of land masses and mountains

• Phase changes of water – moving heat around the system

From S. Rahmstorf: Thermohaline Ocean Circulation. In: Encyclopedia of QuaternarySciences, Edited by S. A. Elias. Elsevier, Amsterdam 2006 (see www.pik-potsdam.de/~stefan/thc_fact_sheet.html)

Ocean Energy Transport

Global Water Cycle: Phase changes of water move heat around

the system

Units 1012 m3/year

Annual Mean Precipitation (Rain and Snow: mm/day)

Global Water Cycle: Phase changes of water move heat around

the system

Annual Mean Precipitation minus Evaporation (mm/day)

Precipitation = Surface Evaporation + Atmospheric Transport

Global Water Cycle: Phase changes of water move heat around

the planet

Annual Mean Sea Surface Salinity reflects the global water cycle

How much of this did we know when I began my career in 1972?

A little bit about the oceans and a little bit about global weather

X X

? ?

None of the global budgets, none of the hydrological cycle

Climate Model simulation of Net

Radiation and Atmospheric

Transports. Ocean transports are inferred

as a residual.

Climate models were beginning to tell us things about the climate system that we couldn’t

observe.

Content DividerWhat is Climate Modelling?

Climate Models are based on fundamental equations of motion (Newton’s 2nd Law of Motion), mass continuity, moist thermodynamics and radiative transfer

These govern:

• Flow of air and water - winds in the atmosphere, currents in the ocean.

• Exchange of heat (sensible and latent) and momentum between the atmosphere and the earth’s surface

• Release of latent heat by condensation during the formation of clouds and raindrops

• Absorption of solar radiation and emission of thermal (infra-red) radiation

Building a Climate Model: Where to Start?

Represent the earth by a grid of squares, typically of length 100 km or smaller. Atmosphere and oceans are divided into vertical slices of varying depths, typically 70 or more. 3-dimensional picture of the state of the atmosphere and oceans. Integrate equations of motion and thermodynamics forward in time.

Fundamentals of climate (and weather) modelling

Representing Unresolved Processes: Parametrization

Boundary layer turbulence and mixing Cumulus convection

Radiation PrecipitationClouds and

microphysicsAtmospheric composition

Effects of mountains

© Crown copyright Met Office

Evolution of climate models over time: Resolution

1990 2001

1996 2007

Evolution of climate models over time: Complexity

Earth Observation – giving the planet a ‘health check’!

We know an immense amount about what is happening to the planet – but we don’t necessarily know why

Content DividerClimate Models as the ‘Laboratories’ of Climate Science

Climate models were beginning to tell us things about how the climate system works and what’s

important

Does soil moisture affect the behaviour of the West African Monsoon?

Wet Soil

Dry Soil

Predicting Winter Climate: Understanding the drivers of the

North Atlantic Oscillation

© Crown copyright Met Office

Understanding WHY the world is warming

‘Extremely likely (95-100%) that most of observed increase in global surface temperature since 1951 has been caused by human influence.’ – IPCC 2013

‘Hiatus’ in global surface warming

Spatial Pattern of the ‘Hiatus’ hints at the oceans

Sea Surface Temperature

2000-2012 minus 1990-1999

From Meehl et al. 2013

Pacific Ocean implicated in the ‘hiatus’ in models

From Meehl et al. 2013

Models suggest that heat is sequestered into the deep ocean

during a ‘hiatus’

Content DividerClimate modelling: A modern Renaissance Science?

tan2 sin

cocos

s2r pd v uuw

wr r

cD uv S

Dt r

uv

2 tan2 sin pd vr

c vw

r r

u

r

D vu S

Dt

2 2

2 cos wpd

rvcr r

g

u vu S

D w

Dt r

2 2cos cos 0cos

ry y

D u v w

Dt rr r

r r

rD SDt

Met Office Unified Model makes neither hydrostatic or shallow atmosphere approximations

Mathematics

Mathematics

v

How to solve these equations numerically on a grid: Accuracy and Conservation of fundamental properties Efficient and Scalable code Robust and Stable code

Icosahedral-triangles Icosahedral-hexagons Cubed Sphere

Original weather forecasts so simple that they can run on a mobile phone in fractions

of a second

Met Office’s current IBM Power7 machine has peak speed of ≈ 1Petaflop

(1,000,000,000,000,000 sums per second)

Mathematics, Computer Science

Some of the Machines that I’ve worked on!

1980s: NCAR Cray 1 2000s: Japanese Earth Simulator

2010s: Met Office IBM Power 7

Mathematics, Computer Science, Newtonian Physics

Geophysical flows: Newton’s Laws of

Motion on a Rotating Sphere

Ocean surface temperatures simulated by 2km ocean model.

Image courtesy of the Mercator Ocean Project, France

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics

Climate Model (HADGEM2-ES) precipitation

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer

Gases absorb and emit infrared radiation in distinct spectral bands

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics

Source: Tollefson, Nature News, 2012

© Crown copyright Met Office

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry, Biology

Microbial structuring of marine ecosystems

How water moves through a tree

© Crown copyright Met Office

Screenshot from a Met Office Climate Model simulation at 12km

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry, Biology, Meteorology

THE VIDEO HAS BEEN REMOVED FROM THIS SLIDE IN ORDER TO MAKE THE PRESENTATION AVAILABLE ONLINE.

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry, Biology, Meteorology, Oceanography

Gulf Stream meanders in 1/40 ocean modelMet Office Climate Model

Met Office Ocean Model with no ocean-atmosphere interaction

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry, Biology, Meteorology, Oceanography, Terrestrial Ecosystems

From O’Connor et al. 2011 (Met Office Hadley Centre)

Future Methane Emissions

Modelling the Carbon Cycle

Phytoplankton (algal) blooms around the UK Image from Western Channel Observatory

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry, Biology, Meteorology, Oceanography, Terrestrial Ecosystems, Marine Ecosystems

Chlorophyll (April 2008)

Chlorophyll from the Met Office’s NEMOShelf-ERSEM operational model. The yellow and orange regions show areas of algal blooms.

Met Office Climate Model: Understanding the Arctic energy budget

Mathematics, Computer Science, Newtonian Physics, Moist Thermodynamics, Radiative Transfer, Particle Microphysics, Chemistry, Biology, Meteorology, Oceanography, Terrestrial Ecosystems, Marine Ecosystems, Cryosphere.......

1980

2012

Loss of Arctic Summer Sea Ice

© Crown copyright Met Office

It works! Fundamental constraints. AR5 model biases or HadGEM2-ES results?

Putting it all together: Holistic Earth SystemBasic Constraints: Energy Input from the Sun, Rotation

Rate of the Planet, (Atmospheric Composition)

It Works!

Sea Surface Temperature biases in Met Office Earth

System Model (HadGEM2-ES)

Storm Tracks in observations and

HadGEM2-ES

Observations HadGEM2-ES

Climate modelling: A Predictive Science

Taking the Earth into uncharted territory?

Human Perturbations to the Carbon Cycle

© Crown copyright Met Office

Results from my first study on CO2:The effects of doubling CO2 concentration on

Radiative-Convective equilibrium

T(K) 270 280 290 300

DT(PC) 1.52 1.57 1.65 1.70

DT(CA) 1.56 1.68 1.92 2.46

Effect of doubling CO2 based on two cumulus convection schemes

T(K) 270 280 290 300

DT(PC) 1.40 1.44 1.40 1.40

DT(CA) - 1.64 1.88 2.20

NO CLOUDS

WITH CLOUDS

Projections of future temperature rise

• Global warming >2˚C is likely for scenarios with little mitigation of emissions. No mitigation leads to a world more than 4˚C warmer than pre-industrial times Inter-Governmental Panel on Climate Change (2013)

Projections of future sea level riseLong Term Commitment to Climate Change

• Global average sea level will rise during the 21st century; it is very likely that it will rise faster than it has during the last 40 years.

Inter-Governmental Panel on Climate Change (2013)

There will be large geographical variations

Inter-Governmental Panel on Climate Change (2013)

So if climate models are such an achievement, why are we still uncertain?

© Crown copyright Met Office

Uncertainty comes from:

• Natural variability

• Model uncertainty

• Scenario uncertainty

Relative importance of each source of uncertainty in decadal mean surface air temperature predictions

From Hawkins and Sutton (2009)

MODEL

SCENARIO

VARIABILITY

Representing Unresolved Processes: Parametrization

Boundary layer turbulence and mixing Cumulus convection

Radiation PrecipitationClouds and

microphysicsAtmospheric composition

Effects of mountains

Climate modelling: Helping us Plan for a Safe and Sustainable Future

‘Circle of Securities’

Climate Variability and Change

UrbanisationPopulation growth

Water

Economic

Food

EnergyPolitical

Health

Migration

© Crown copyright Met Office

© Crown copyright Met Office

Climate Service UKWorking together to prepare for tomorrow

• Saving lives and livelihoods

• Delivering resilience and preparedness

• Making wise choices for future adaptation

• Avoiding dangerous climate change

• Supporting growth and the green economy

© Crown copyright Met Office

• 1953 East coast storm surge killed 307 in the UK and flooded 32,000 industrial facilities

• Estimated £200bn value of property in Thames floodplain, 1.1 million employees, 55,000 properties

• TE2100 science avoided up to £20bn capital expenditure through more robust predictions and scenarios

• Based on fundamental and immutable laws• Include many science disciplines – ‘renaissance’ science• Arguably the largest and most complex codes ever

written • Simulate the wealth of processes and phenomena in

the climate system • Enable us to understand how the climate system works• Enable us understand why climate is changing

• Enable us to ‘see into the future’ and take action

Scale of the Enterprise to match the Scale of the Challenge

To Recap

‘For the Relief of Man’s Estate’

“For men have entered into a desire of learning and knowledge, sometimes upon a natural curiosity and inquisitive appetite; sometimes to entertain their minds with variety and delight; sometimes for ornament and reputation; and sometimes to enable them to victory of wit and contradiction; and most times for lucre and profession; and seldom sincerely to give a true account of their gift of reason, to the benefit and use of men: …… a rich storehouse, for the glory of the Creator and the relief of man's estate. “

Francis Bacon, The Advancement of Learning (1605)

“I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.” Isaac Newton

Climate Modelling – Work in Progress

Why Climate Models are the Greatest Feat of Modern Science

Have I convinced you?