climate modelling: latest results and implications for

Climate modelling: latest results and implications for decision makersChris JonesMet Office Hadley Centre Rossby Centre Day, May 6th 2013


Data and decisions?

What's missing?

Data Decisions??


Data and decisions?

What's missing? A big computer?

Data Decisions??


Data and decisions?

What's missing? Science!

Data DecisionsSCIENCE

knowledge

Data

understanding


Overview

Brief history of the science Importance of the understanding

What's new? IPCC “RCP” scenarios Modelling results (the “data”) Interpretation (the “science”)

Policy implications


“on the shoulders of giants”

Supercomputers and complex climate models are relatively new But meteorology and climate science are not

Here's just a handful of influential people...


Carl-Gustaf Rossby

1898 – 1957 Swedish Studied meteorology and oceanography under

Bjerknes Pioneered understanding of large-scale motions of

the atmosphere as a problem in fluid-dynamics With Ertel, derived mathematical formulation

of Rossby waves Later, championed atmospheric chemistry research


George Hadley

1685 - 1768 British Lawyer and amateur meteorologist Pioneered understanding trade-winds and the

atmospheric forcing behind them Did not yet recognise angular momentum –

theory based on linear momentum – but demonstrates insight


Svante Arrhenius

1859 - 1927

Swedish

Taught himself to read at 3... and a distinguished chemist (“activation energy”)

Greenhouse effect

– As a theory known before Arrhenius

– Derived logarithmic relationship between CO2 and temperature change

Recognised that human emissions of CO2 might be enough to change our climate (including water vapour feedback)


Lewis Fry Richardson

1881 - 1953 British First idea of “numerical weather prediction” -

numerically solving differential equations to progress forwards by finite time periods

Pre-dated computers to be able to implement/test

Basic idea now forms core of (almost) all weather/climate prediction

2013 is 100th Anniversary of LFR joining the UK Met Office – as an observer at Eskdalemuir


Lewis Fry Richardson

Imagine a large hall like a theatre... the walls are painted to form a map of the globe

A myriad of computers [people] are at work [for their own part of the map]

“In a neighbouring building there

is a research department, where

they invent improvements...”


The basis of our science

Myth: “climate predictions are based on the findings of computer models”

Fact: the basic science of our atmosphere, and earth-system has been known for centuries

Very well known, established physical laws

Long pre-dates invention of computers

Today we use computers to put numbers in these equations, and to generate and process data in great quantitative detail

But this is meaningless unless it is based on sound, robust science knowledge and understanding


Overview

Brief history of the science Importance of the understanding

What's new? IPCC “RCP” scenarios Modelling results (the “data”) Interpretation (the “science”)

Policy implications

RCP scenarios• New climate scenarios

• “RCP”s: Representative Concentration Pathway

• Span published scenarios

• 324 considered

• 32 met list of criteria

• 4 selected

• 10th – 90th percentiles

• 4 different IAMs

• Labelled by radiative forcing at 2100

• Moss et al., 2010, Nature

RCP scenarios

• Prescribed CO2 concentration– And other GHGs,

aerosols

• Time-varying land-use

Climate model resolution improves

HadGEM2


Models capture finer detail

Summer temperature difference (°C) between the end of the 21st century and the present

Not yet run globally, but see CORDEX talk...

Climate models include more factors


Earth system modelling

Direct link from human activity (emissions, land-use...) to climate and its impacts back on society

Temperature

Temperature

Notice the stabilisation

Precipitation

Spatial changes by 2100

Sea level riseThermal expansion component

Sea level riseThermal expansion component

Notice no stabilisation

Permafrost area

Compatible fossil fuel emissions

• Earth System Models (“ESMs”) simulate land/ocean carbon fluxes

• CO2 concentration driven by surface sources and sinks

• RCP simulations prescribe atmospheric CO2• If we know the natural carbon sinks/sources• We can diagnose the anthropogenic

emissions required to follow RCP pathway

Compatible fossil fuel emissions

Jones et al., 2013, J. Clim.

• ESMs simulate land/ocean carbon fluxes– Diagnose emissions required to follow RCP

pathway

Redefining climate sensitivity

“Equilibrium Climate Sensitivity”, ECS

Long-term climate change due to doubling of CO2

“Transient Climate Response”, TCR

Actual climate change at time of CO2 doubling (idealised CO2 rise at 1% per year)

Both these measures only consider climate response to CO2

Neither consider CO2 response to climate

But it's a coupled system...

• … feedbacks are significant

TCRE: linking emissions to climate

Many different emissions profiles that release the same cumulative amount of CO2

Global warming very strongly linked (linearly) with total emission

- less dependent on the pathway

Concept of TCRE: transient response to cumulative emissions

Observationally constrained close to 2o per trillion tonnes Allen et al., Nature, 2009;

Gillett et al, J. Climate, 2013

From data to decisions?

Framing results for policy makers

- couple of quick examples- benefits and achievability of RCP2.6


The impact of a global temperature rise of 4 ºC

Change in temperature from pre-industrial climate

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Current City population • 3-10 million • 10-20 million

Meltingice

OceanAcidification

Rainforestloss

Reduced crops

Forestfire

Increased drought

Stronger tropical storms

Methane release

More heatwaves

“Avoided” changes by 2100

RCP2.6 – requirement for negative emissions?


Foss

il fu

el e

mis

sion

s

Achieving 2 degrees?


“suc

cess

”

“achievability”

Conclusions

Climate science >100 years old! Based on deep understanding of robust physical

laws Numerical methods provide quantification of these

New RCP scenarios include climate mitigation policy

Climate Models (Earth System Models) include more relevant processes

help answer how to achieve these scenarios - more direct links from emissions to climate to

impacts improve our ability to inform decisions

climate modelling: latest results and implications for

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