climate modelling: latest results and implications for
TRANSCRIPT
Climate modelling: latest results and implications for decision makersChris JonesMet Office Hadley Centre Rossby Centre Day, May 6th 2013
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Data and decisions?
What's missing?
Data Decisions??
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Data and decisions?
What's missing? A big computer?
Data Decisions??
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Data and decisions?
What's missing? Science!
Data DecisionsSCIENCE
knowledge
Data
understanding
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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
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“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...
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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
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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
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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)
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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
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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...”
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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
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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
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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
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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
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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?
Jones et al., 2013, J. Clim.
Foss
il fu
el e
mis
sion
s
Achieving 2 degrees?
Jones et al., 2013, J. Clim.
“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