Introduction to Climate Change Scenario Development

1
Introduction to Climate Change Scenario
Development
Dr. Elaine Barrow CCIS Principal Investigator
(Science)
2
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 a
plausible future climate that has been
constructed for explicit use in investigating the
potential consequences of anthropogenic climate
change IPCC TAR, 2001
3
A climate scenario is not a prediction of future
climate!
4
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

5
Key component of a framework for conducting
integrated assessment of climate change for
policy applications
6
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

7
What you want
typically is daily weather for a particular
place for some future year
8
Three ways ...
COMPLEXITY

• Incremental (arbitrary, synthetic) scenarios
• Analogue scenarios
• Scenarios from global climate models (GCMs)

9
Incremental Scenariosfor sensitivity studies

• Can provide valuable information about
• sensitivity
• thresholds or discontinuities of response
• tolerable climate change

10
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)
11
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

12
Spatial Analogues
Source Parry Carter, 1988

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

• 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

13
Temporal Analogues

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

14
Palaeoclimatic Analogues

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

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

IPCC, 1990
15
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

16
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
17
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)
18
Instrumental Analogues
Palmer Drought Severity Index (PSDI) for the US
Corn Belt, 1930-1980.
Source Rosenberg et al., 1993
19
Instrumental Analogues

• Rice-growing areas in Japan

0.4C warmer than base
Base, 1951-1980
Warm decade, 1921-1930
20
Instrumental Analogues

• ADVANTAGES
• data available on a daily and local scale
• scenario changes in climate actually observed and
  so are internally consistent and physically
  plausible

• DISADVANTAGES
• 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

21
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
22
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
23
GCM evolution
EQUILIBRIUM EXPERIMENTS
1980s
TRANSIENT EXPERIMENTS
late 1980s
COLD START
WARM START
early 1990s
24
Warm start GCMs
25
CGCM1
26
Which GCM should I use?

• Vintage
• Resolution
• Validity
• Representativeness of results
• Source Smith and Hulme, 1998

27
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

28
Climate models are not accurate ...
29
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
DTt2-t1
Some models exhibit large inter-decadal
variability, so average over 30 years to capture
longer-term trend.
30
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

31
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

32
Sources of Uncertainty
Cascade of uncertainty
Source Hadley Centre for Climate Prediction
and Research, UK Met. Office
33
The future is uncertain ...
IPCC Special Report on Emissions Scenarios (2000)
34
The future is uncertain ...
35
The future is uncertain ...
1.4-5.8C
36
The future is uncertain ...
0.09-0.88m
37
SRES climate change
38
SRES climate change
39
Different GCMs give different results
40
Different GCMs give different results
41
Which scenarios?
Cooler, wetter
Warmer, wetter
Cooler, drier
Warmer, drier
42
Risk assessment approach

• ADVANTAGES
• makes (some) uncertainties explicit
• good for risk assessment
• can be applied at different scales

• DISADVANTAGES
• not yet a well developed methodology
• requires a lot of model data to develop
• expert assumptions still needed

43
Effect of scenario resolution on impact outcome
Spatial Scale of Scenarios
Source IPCC, WGI, Chapter 13
44
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?

45
Further Reading

• IPCC TAR - Chapter 13 (www.ipcc.ch)
• Smith Hulme - Chapter 3 Handbook on Methods of
  Climate Change Impacts Assessment and Adaptation
  Strategies (http//130.37.129.100/english/o_o/inst
  ituten/IVM/research/climatechange/Handbook.htm)
• Parry Carter - Climate Impact and Adaptation
  Assessment. Earthscan, 166pp.
• IPCC TGCIA Guidelines on Climate Scenarios
  (currently under revision)