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Introduction to Climate Change Scenario Development. Dr. Elaine Barrow CCIS Principal Investigator (Science). What is a climate change scenario?. Definitions: “…a coherent, internally consistent and plausible description of a possible future state of the world…” [Parry & Carter, 1998]

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introduction to climate change scenario development
Introduction to Climate Change Scenario Development

Dr. Elaine Barrow

CCIS Principal Investigator (Science)

what is a climate change scenario
What is a climate change scenario?


“…a coherent, internally consistent and plausible description of a possible future state of the world…”

[Parry & Carter, 1998]

“…a plausible future climate that has been constructed for explicit use in investigating the potential consequences of anthropogenic climate change…”

[IPCC TAR, 2001]

why do we need climate change scenarios
Why do we need climate change scenarios?
  • To provide data for VIA assessment studies
  • To act as an awareness-raising device
  • To aid strategic planning and/or policy formation
  • To scope the range of plausible futures
  • To structure our knowledge (or ignorance) of the future
  • To explore the implications of decisions

Key component of a framework for conducting integrated assessment of climate change for policy applications

what are the challenges of developing climate scenarios
What are the challenges of developing climate scenarios?
  • simple to obtain, interpret and apply
  • provide sufficient information for VIA assessments
  • physically plausible and spatially compatible
  • consistent with the broad range of global warming projections
  • reflect the potential range of future regional climate change, i.e., be representative of the range of uncertainty in projections
what you want
What you want …

… typically is daily weather for a particular place for some future year


Three ways ...


  • Incremental (arbitrary, synthetic) scenarios
  • Analogue scenarios
  • Scenarios from global climate models (GCMs)
incremental scenarios for sensitivity studies


Incremental Scenariosfor sensitivity studies

Can provide valuable information about:

  • sensitivity
  • thresholds or discontinuities of response
  • tolerable climate change

ADVANTAGES: simple to construct and apply, allow relative sensitivity of impacts sectors/models to be explored

DISADVANTAGES: arbitrary (and unrealistic) changes, may be inconsistent with uncertainty range

Yield change (t/ha) of Valencia orange in response to changing temperature and CO2 concentration [Source: Rosenzweig et al. (1996)]

analogue scenarios
Analogue Scenarios

Identification of recorded climate regimes which may resemble the future climate in a given region

Assumption: climate will respond in the same way to a unit change in forcing despite its source and even if boundary conditions differ

spatial analogues
Spatial Analogues

Identify regions which today have a climate analogous to that anticipated in the study region in the future

[Source: Parry & Carter, 1988]

  • Approach restricted by frequent lack of correspondence between other non-climatic features of the two regions
  • Causes of the analogue climate likely different from the causes of future climate change
temporal analogues
Temporal Analogues

Use climate information from a past time period as an analogue of possible future climate

  • Palaeoclimatic
  • Instrumental
palaeoclimatic analogues
Palaeoclimatic Analogues

Use information from the geological record - fossils, sedimentary deposits - to reconstruct past climates

  • mid-Holocene, 5-6k BP, 1°C warmer
  • last (Eemian) interglacial, 125k BP, approx. 2°C warmer
  • Pliocene, 3-4m BP, 3-4°C warmer

IPCC, 1990

palaeoclimatic analogues1
Palaeoclimatic Analogues
  • changes in the past unlikely to have been caused by increased GHG concentrations
  • data and resolution generally insufficient, i.e., extremely unlikely to get daily resolution and individual site information
  • uncertainty about the quality of palaeoclimatic reconstructions
  • higher resolution (and most recent) data generally lie at the low end of the range of anticipated future climatic warming
instrumental analogues

Difference =0.4°C

Instrumental Analogues

Past periods of observed global- or hemispheric- scale warmth used as an analogue for the future

Northern Hemisphere temperature record

Lough et al., 1983

instrumental analogues1
Instrumental Analogues

The 1930s in the North American Great Plains have frequently been used as an analogue for the future.

Mean temperature (°C)

Precipitation (mm)

Differences between 1931-1940 average and 1951-1980 average in the MINK states (Easterling et al., 1992)


Instrumental Analogues

Palmer Drought Severity Index (PSDI) for the US Corn Belt, 1930-1980.

[Source: Rosenberg et al., 1993]

instrumental analogues2
Instrumental Analogues

Rice-growing areas in Japan

0.4°C warmer than base

Base, 1951-1980

Warm decade, 1921-1930

instrumental analogues3
Instrumental Analogues


  • data available on a daily and local scale
  • scenario changes in climate actually observed and so are internally consistent and physically plausible
  • climate anomalies during the past century have been fairly minor cf. anticipated future changes
  • anomalies probably associated with naturally-occurring changes in atmospheric circulation rather than changes in GHG concentrations
scenarios from gcms
Scenarios from GCMs

GCMs are the

“…only credible tools currently available for simulating the physical processes that determine global climate...”[IPCC]

[Source: David Viner, UK Climate Impacts LINK Project]

what do gcms do
What do GCMs do?

Simulate the response of the global climate system to changes in atmospheric composition

Growth in population, energy demand, changes in technology and land-use/cover

Energy-economy models

Greenhouse gas emissions

Carbon cycle and other chemical models

Atmospheric GHG concentrations

Climate models

Future climate projections

gcm evolution
GCM evolution



late 1980s



early 1990s


which gcm should i use
Which GCM should I use?
  • Vintage
  • Resolution
  • Validity
  • Representativeness of results

[Source: Smith and Hulme, 1998]

BUT ...
  • Climate models are not accurate
  • Different GCMs give different results
  • The future is uncertain - it is expensive to run many climate change experiments using different emissions scenarios
  • Climate model results are not at a fine enough spatial scale
so we cannot use their output directly

Climate change integration


Global mean temperature (°C)



so we cannot use their output directly ...

t1 is typically 1961-1990

t2 is a future time period, e.g., 2040-2069, representing the 2050s


Some models exhibit large inter-decadal variability, so average over 30 years to capture longer-term trend.

ipcc tgcia recommend 1961 1990 as the climatological baseline
IPCC-TGCIA recommend 1961-1990 as the climatological baseline

Role in climate scenario construction:

  • serves as a reference period from which estimated future change in climate is calculated
  • used to define the observed present-day climate with which climate change scenario information is usually combined
specifying the baseline
Specifying the Baseline

Important for:

  • characterising the prevailing conditions under which an exposure unit functions and to which it must adapt
  • describing average conditions, spatial and temporal variability and anomalous events, some of which can cause significant impacts
  • calibrating and testing impact models across the current range of variability
  • identifying possible ongoing trends or cycles
  • specifying the reference situation with which to compare future changes

Sources of Uncertainty

Cascade of uncertainty

[Source: Hadley Centre for Climate Prediction and Research, UK Met. Office]

the future is uncertain
The future is uncertain ...

IPCC Special Report on Emissions Scenarios (2000)


Which scenarios?

Cooler, wetter

Warmer, wetter

Cooler, drier

Warmer, drier


Risk assessment approach

  • makes (some) uncertainties explicit
  • good for risk assessment
  • can be applied at different scales
  • not yet a well developed methodology
  • requires a lot of model data to develop
  • expert assumptions still needed

Scenario Needs

  • What climate variables are essential for your study?
  • How many scenarios do you want? Which uncertainties are you going to explore?
  • Do you need local data for case studies/sites, or national/regional coverage?
  • What spatial resolution do you really need - 300km, 100km, 50km, 10km, 1km? Can you justify this choice?
  • Do you need changes in average climate, or in variability?
  • Do you need changes in daily weather, or just monthly totals?
further reading
Further Reading
  • IPCC TAR - Chapter 13 (
  • Smith & Hulme - Chapter 3: Handbook on Methods of Climate Change Impacts Assessment and Adaptation Strategies (
  • Parry & Carter - Climate Impact and Adaptation Assessment. Earthscan, 166pp.
  • IPCC TGCIA Guidelines on Climate Scenarios (currently under revision)