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

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. Guidelines for discussing climate change

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

Trends – total monthly rainfall: South Africa: past changes are real, measurable and significant Remember: it’s not only the average that is important!

50-year change in the average number of raindays in April (blue = increase) Historical change – Precipitation Smaller changes in the mean, larger changes in other attributes

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 Projecting the future Confidence in regional projections based on four sources of information:

GCM simulations of the future Limited in simulation of regional scales Mean precipitation change from 20 GCM simulations for JJA, DJF, and annual (IPCC AR4 Model archive) Summer WinterAnnual 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.

Projected summer rainfall changes Downscaled from GCM simulations The pattern response is largely independent of emissions scenario Downscaling:

Breakdown of one projection to monthly resolution: change in number of raindays > 2mm [PMG note: maps not included, please

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

Treating the coupled system Regional climates can respond significantly to land use change Relevant for societal land use response to future climate change Change one component, see response in another aspect. A critical need to understand the coupling.

Other dangerous developments: tipping points There are identified mechanisms that can potentially give rise to acceleration of change Examples: - Melting of Siberian permafrost - Soil outgassing - Ocean floor methane hydrates - etc…

Some Conclusions 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 The projected climate change that shows consensus from multiple information sources, indicate the following:

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