Global Climate Change: Implications for South Africa

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Global Climate Change Implications for South
Africa
Bruce Hewitson Climate Systems Analysis Group
(CSAG), University of Cape Town
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Climate change weather versus climate
Climate defines the envelope within which weather
events take place. Weather events are governed
by the large scale processes of the
atmosphere As the large scale processes change,
so does the regional manifestation of weather
events One cannot attribute a single event to
climate change
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Guidelines for discussing climate change

• Change is both complex and simple beware
  over-simplifying the complex, or confuse the
  simple
• Change has elements that are immediate the long
  term care not to ignore one at the expense of
  the other.
• Understand the limitations and uncertainty it is
  easy to over-interpret what is not yet known.
• The change in the average is very different to
  change in attributes.
• Recognize there is often media distortion go to
  the source.

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First level response is in global
temperature 1998 was warmest on record, 2005 may
exceed this
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Warmest on record
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Global changes and remote changes have local and
regional consequences e.g. opening of northwest
passage Indirect impacts on both environment
and economy of South Africa
Arctic sea ice extent
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South Africa past changes are real, measurable
and significant Remember its not only the
average that is important!
Trends total monthly rainfall 1950-1999
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Historical change Precipitation Smaller changes
in the mean, larger changes in other attributes
50-year change in the average number of raindays
in April (blue increase)
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Projecting the future Confidence in regional
projections based on four sources of information

• Global Climate Models simulate climate response
  
• Forced by emission scenarios, skillful for large
  scale processes
• Regional Climate Model downscaling
• A maturing tool South Africa woefully
  under-resourced
• Empirical/Statistical downscaling
• Effective tool appropriate for many impact
  studies
• Physically plausible mechanisms
• Regional interpretation from projections of
  large scale processes

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GCM simulations of the future Limited in
simulation of regional scales
Winter
Annual
Summer
Mean precipitation change from 20 GCM simulations
for JJA, DJF, and annual (IPCC AR4 Model archive)
For now, pattern of change more important than
magnitude
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Downscaling Translating between the large scale
changes and regional scales of adaptation. In
some aspects, UCT is a world leader.
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Downscaling
Projected summer rainfall changes Downscaled
from GCM simulations The pattern response is
largely independent of emissions scenario
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Breakdown of one projection to monthly
resolution change in number of raindays gt
2mm PMG note maps not included, please email
info_at_pmg.org.za
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Uncertainty is real There are gaps in our
knowledge
Source of uncertainty Natural variability Future
emissions Knowledge uncertainty Science
uncertainty
Possible solutions Long term ensembles Span the
envelope of scenarios More research!!!! Model
physics ensembles
These are constraints not failures The primary
limitation in Africa toward reducing uncertainty
is the available capacity to explore these
questions
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Treating the coupled system
Change one component, see response in another
aspect. A critical need to understand the
coupling.
Regional climates can respond significantly to
land use change Relevant for societal land use
response to future climate change
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Other dangerous developments tipping points

• Examples
• Melting of Siberian permafrost
• Soil outgassing
• Ocean floor methane hydrates
• etc

There are identified mechanisms that can
potentially give rise to acceleration of change
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Some Conclusions
The projected climate change that shows consensus
from multiple information sources, indicate the
following

• Warmer temperatures everywhere, more so in the
  interior.
• Wetter conditions on the east coast,
  particularly on the escarpment
• Drier conditions in the far west
• Drier Western Cape away from the mountains
• The position of boundaries of change is
  uncertain
• Increased rainfall intensity and extreme events
• Suggestions of increased inter-annual variability

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Primary challenges

• Build capacity to
• undertake the development of regional
  projections
• improve understanding of local scale feedbacks
  (especially land use change)
• develop the communication from science to those
  engaged in adaptation, management, and policy
• engage with multi-disciplinary research to
  leverage existing expertise