Transcript Regional climate change under high-end global warming

Regional Temperature and
Precipitation changes under highend global warming
Michael Sanderson, Deborah Hemming, Richard Betts
Met Office Hadley Centre, 12 May 2010
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Contents
This presentation covers the following areas
• Introduction
• Methodology
• Temperature and Precipitation changes
• Regions most strongly impacted
• Summary
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Introduction
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AR4 Projections
HighEnd
EU
Limit
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Current global temperature
projections
• IPCC AR4: Temperatures will rise between 1.6
and 6.9C by 2100 (relative to preindustrial).
• Much EU political attention focused on 2C
warming.
• However, climate projections clearly indicate
greater levels of global warming are possible.
• Projections of 4C or more termed ‘high-end’.
• This work was funded by the Joint DECC and
Defra Integrated Climate Programme DECC/Defra (GA01101) (and contributes to the
AVOID project).
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High-End Climate Change
1. Are high-end climate projections notably
different to the non high-end projections?
2. Which regions are likely to be most affected
by high-end changes?
•
AR4 model ensemble analysed, focusing on
results using SRES A2 scenario (19 models).
•
Analysed monthly mean data.
•
2 m Temperature, Total Precipitation.
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Methodology (1)
• Calculate annual global average temperature
for preindustrial control run and 2090-2099.
• If more than 1 model realisation, each one
treated independently.
• 40 projections analysed.
• If temperature difference is 4C (to 1 d.p.) or
more, that projection classed as high-end.
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Summary of Global Mean
Temperature Changes
• 21 model projections classed as high-end
• 19 projections are non high-end.
• In high-end projections 4ºC first reached between
2083 and 2094.
• 2090s mean temperature changes lie between 4.0
and 4.8ºC
• A few other models reach or exceed 4ºC in
individual years during 2090s but are not classed as
high-end.
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Model biases
• Correlation between temperature change and
preindustrial mean temperature examined using
all projections.
• Models which simulate the large areas of ice in
the polar regions will have coldest temperatures
for the preindustrial period
• Only these models could produce a large
warming as the ice sheets recede.
• No correlation observed, indicating that any
relationship between preindustrial ice sheet
extent and temperature increases is complex
and non-linear.
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Methodology (2)
• Examined changes in temperature and
precipitation between pre-industrial and future.
• December, January and February (DJF) and
June, July and August (JJA).
• For future used average of 2070-2099.
• Changes scaled with that model’s global
warming.
• Medians of high-end and non high-end models
examined.
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DJF Scaled Temperature changes +
model range
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JJA Scaled Temperature changes +
model range
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Summary of Temperature
Changes
• Very large warming projected over much of high
northern latitudes in DJF (4ºC per degree).
• Range of temperature changes from models
larger than median temperature rise.
• Large biases in modelled ice sheet extents
• Many land areas warm by 1.4-2.0 ºC in JJA.
• Area of cold water projected to form in North
Atlantic and southern ocean (vertical mixing).
• Regional response of high-end and non highend models is similar, except over Asia.
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Precipitation Changes (%)
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Summary of Precipitation
Changes
• Patterns of precipitation changes from high-end
models similar to non high-end models.
• Large reductions in many areas between 45 ºN
and 45 ºS.
• Bigger reductions in high-end models.
• Precipitation increases north of 45 ºN and south of
50 ºS.
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Regions impacted by highend climate change
• High-end and non high-end models project
similar patterns of temperature and precipitation
change.
• Results from all models scaled to a global
average temperature rise of 4ºC.
• Looked for regions where temperature rise by at
least 6ºC and precipitation changes by ±10%.
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Areas where:
P  ±10%
T  6ºC
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Summary
• Many high northern latitudes projected to incur
large temperature and precipitation increases.
• Mexico and northern Africa projected to be at
risk from high-end climate change in DJF.
• Southern Europe and the adjacent part of
central Asia, and southern Africa at risk in JJA.
• Regional temperature response of high-end
models and non high-end models very similar.
• DJF, uncertainty mostly from temp changes.
• JJA, uncertainty mostly from precip changes.
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Questions and answers
[email protected]
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