Global Climate Change: Implications for South Africa Bruce Hewitson: Climate Systems Analysis Group (CSAG), University of Cape Town.

Global Climate Change: Implications for South AfricaGlobal 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 Climate defines the envelope within which weather events take place. which weather events take place.

Weather events are governed by the Weather events are governed by the large scale processes of the atmospherelarge scale processes of the atmosphere

As the large scale processes change, so As the large scale processes change, so does the regional manifestation of does the regional manifestation of

weather eventsweather events

One cannot attribute a single event to One cannot attribute a single event to climate changeclimate change

a)a) Change is both complex and simple: Change is both complex and simple: beware over-simplifying the complex, beware over-simplifying the complex, or confuse the simpleor confuse the simple

b)b)Change has elements that are Change has elements that are immediate the long term: care not to immediate the long term: care not to ignore one at the expense of the ignore one at the expense of the other.other.

c)c) Understand the limitations and Understand the limitations and uncertainty: it is easy to over-uncertainty: it is easy to over-interpret what is not yet known.interpret what is not yet known.

d)d)The change in the average is very The change in the average is very different to change in attributes.different to change in attributes.

e)e) Recognize there is often media Recognize there is often media distortion … go to the source.distortion … go to the source.

Guidelines for discussing climate changeGuidelines for discussing climate change

First level response is in global temperatureFirst level response is in global temperature1998 was warmest on record, 2005 may exceed this1998 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: 1950-1999Trends – total monthly rainfall: 1950-1999

South Africa: past changes are real, measurable and significantRemember: it’s not only the average that is important!

50-year change in the average number of raindays in April (blue = increase)

Historical change – PrecipitationHistorical change – PrecipitationSmaller changes in the mean, larger changes in other Smaller changes in the mean, larger changes in other attributes attributes

a)a) Global Climate Models – simulate climate Global Climate Models – simulate climate response response

Forced by emission scenarios, skillful for large Forced by emission scenarios, skillful for large scale processes scale processes

b)b)Regional Climate Model downscalingRegional Climate Model downscaling

A maturing tool; South Africa woefully under-A maturing tool; South Africa woefully under-resourced resourced

c)c) Empirical/Statistical downscaling Empirical/Statistical downscaling

Effective tool appropriate for many impact Effective tool appropriate for many impact studiesstudies

d)d)Physically plausible mechanisms Physically plausible mechanisms

Regional interpretation from projections of large Regional interpretation from projections of large scale processesscale processes

Projecting the futureConfidence in regional projections based on four sources of

information:

GCM simulations of the futureGCM simulations of the future

Limited in simulation of regional scalesLimited in simulation of regional scales

Mean precipitation change from 20 GCM simulations for JJA, DJF, and annual(IPCC AR4 Model archive)

Summer Winter Annual

For now, pattern of change more important than magnitudeFor 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:Breakdown of one projection to monthly resolution: change in number of raindays > 2mm

[PMG note: maps not included, please email [email protected]][PMG note: maps not included, please email [email protected]]

Uncertainty is real: There are gaps in our knowledgeUncertainty is real: There are gaps in our knowledge

Source of uncertaintySource of uncertainty

Natural variability

Future emissions

Knowledge uncertainty

“Science” uncertainty

Possible solutionsPossible solutions

Long term ensembles

Span the envelope of scenarios

More research!!!!

Model physics ensembles

These are constraints … not failuresThese are constraints … not failures

The primary limitation in Africa toward The primary limitation in Africa toward reducing uncertainty is the available capacity reducing uncertainty is the available capacity

to explore these questionsto explore these questions

Treating the coupled systemTreating 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 pointsOther dangerous developments: tipping points

There are identified mechanisms that can There are identified mechanisms that can potentially give rise to acceleration of changepotentially give rise to acceleration of change

Examples:Examples:

- Melting of Melting of Siberian Siberian permafrostpermafrost

- Soil outgassingSoil outgassing

- Ocean floor Ocean floor methane methane hydrateshydrates

- etc…etc…

Some ConclusionsSome 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 challengesPrimary 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