Transcript Climate Systems Analysis Group (CSAG

Global Climate Change: Implications for South Africa
Bruce Hewitson: Climate Systems Analysis Group (CSAG), University of Cape Town
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
Guidelines for discussing climate change
a) Change is both complex and simple: beware
over-simplifying the complex, or confuse the
simple
b) Change has elements that are immediate the long
term: care not to ignore one at the expense of
the other.
c) Understand the limitations and uncertainty: it is
easy to over-interpret what is not yet known.
d) The change in the average is very different to
change in attributes.
e) Recognize there is often media distortion … go
to the source.
First level response is in global temperature
1998 was warmest on record, 2005 may exceed this
Warmest on record
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
South Africa: past changes are real, measurable and significant
Remember: it’s not only the average that is important!
Trends – total monthly rainfall: 1950-1999
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)
Projecting the future
Confidence in regional projections based on four sources of information:
a) Global Climate Models – simulate climate response
Forced by emission scenarios, skillful for large scale processes
b) Regional Climate Model downscaling
A maturing tool; South Africa woefully under-resourced
c) Empirical/Statistical downscaling
Effective tool appropriate for many impact studies
d) Physically plausible mechanisms
Regional interpretation from projections of large scale processes
GCM simulations of the future
Limited in simulation of regional scales
Summer
Winter
Annual
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
Downscaling:
Translating between the large scale changes and regional
scales of adaptation. In some aspects, UCT is a world leader.
Downscaling:
Projected summer
rainfall changes
Downscaled from
GCM simulations
The pattern
response is largely
independent of
emissions scenario
Breakdown of one projection to monthly resolution:
change in number of raindays > 2mm
[PMG note: maps not included, please email [email protected]]
Uncertainty is real: There are gaps in our knowledge
Source of uncertainty
Possible solutions
Natural variability
Long term ensembles
Future emissions
Span the envelope of scenarios
Knowledge uncertainty
More research!!!!
“Science” uncertainty
Model physics ensembles
These are constraints … not failures
The primary limitation in Africa toward reducing
uncertainty is the available capacity to explore
these questions
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
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
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
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