What climate changes will the rise in the atmospheric concentration of carbon dioxide induce over the course of the next several decades?  Several considerations make this question, which is of enormous societal importance,   immensely difficult to answer. First of all we need to know at what rate the concentration will continue to rise; information that requires the prediction of human behaviour.  We can circumvent this formidable problem by asking how climate will change given different rates at which humans burn fossil fuels. It is then possible to pose a number of strictly scientific questions. The first concerns the fate of the carbon dioxide humans inject into the atmosphere. How much will remain there? How much will the plants and the oceans absorb? One component of the ACCESS research programme therefore deals with the bio-geochemical cycles that, potentially, provide an answer. To check the validity of that answer a study of past climates that involved large changes in the atmospheric concentration of carbon dioxide can prove most valuable. Another component of the ACCESS research program is therefore concerned with paleo-climates. To assist policy-makers with immediate answers we can by-pass the difficult questions raised thus far by asking how climate will change in response to specified levels of carbon dioxide. The international scientific community makes such information available on a global scale, to be used in making regional projections for specific countries, a process known as "down-scaling." The ACCESS research programme includes   climate modelling, both dynamical and statistical, that focuses on southern Africa.

Regional Climate Changes

Long term climate changes in Southern Africa are likely to be the result of changes at both the global and regional scale.  The latter are not resolved or understood in the context of a global scale approach. To make societal forecast scenarios meaningful and to implement effective adaptation strategies therefore require regional projections by means of a "downscaling" approach. The primary task is the development of multi-model probabilistic climate change projections, including the underlying methodological approaches, which are tailored and relevant to stakeholders.  This requires

1. The generation and acquisition of multi-model ensemble simulation data for past and future climate.
2. The nesting of regional climate models to generate high resolution scenarios.
3. The development and application of empirical and statistical downscaling models to the multi-model ensemble simulation data.
4. The processing of scenario data in relation to sector-relevant parameters, including extreme events.
5. The generation of uncertainty and probability products to accompany the downscale model projects.
6. The exploration of feedback mechanisms (especially terrestrial) that can change modes of the climate system.
7. A search for thresholds and tipping points that accelerate or abruptly introduce climate changes.
8. The integration of multiple stressors in the analysis of the climate system response.
9. The identification, quantification, and reduction of sources of uncertainty

The Fate of Anthropogenic Carbon

Of the carbon that we inject into the atmosphere by burning fossil fuels, how much will remain in the atmosphere? The answer, which will profoundly affect future climate changes, depends on the rate at which plants, on land and in the oceans, absorb carbon dioxide from the atmosphere.  Southern Africa and its surrounding oceans afford exceptional opportunities for the study of the diverse bio-geochemical processes that are involved. The south-eastern Atlantic, south-western Indian Ocean, and the Southern Ocean are strikingly different. 

Terrestrial (TER) The terrestrial domain covers a wide range of regions from wet equatorial forests, to savannah, grasslands, semi arid Karoo and arid Namib environments. 

South East Atlantic Ocean (ETSA)   The south-east Atlantic encompasses the eastern equatorial system (ETSA) and the wider Benguela upwelling system (BUS) as far south as the sub-tropical convergence.  The upwelling of cold, nutrient-rich water is highly variable in both regions.  The large vertical transport rates make these regions biogeochemically of global importance in respect of both carbon and oxygen fluxes.   

South Atlantic Zone and Southern Ocean (SAZ) These regions, characterized by the sub-tropical convergence zone and energetic meso-scale eddies, could prove to be very important sinks of atmospheric CO₂

The Southern Ocean (SO) poses the major puzzle of being rich in nutrients but   low in chlorophyll concentration.  

The South West Indian Ocean is the "inverse" of the SE Atlantic Ocean: productivity in the coastal zone depends, not on oceanic upwelling, but instead terrestrial sources in the form of river flows which govern salinities and nutrients, both dissolved and particulate.  The unique character of this part of ocean basin is that its biogeochemical characteristics are also very sensitively dependent on direct human activities which change river flow, nutrient fluxes and sediment loads.

The different regions described above are of course strongly linked, by the atmosphere for example. Another link is mediated by the transport of water from the land by means of rivers and estuaries into the coastal oceans. The tools we use here are those of catchment-to-coast studies, and models of individual systems.   

Past Climate Changes
Since the sudden demise of the dinosaurs some sixty million years ago, when the Earth was far hotter than it is today, the drifting of continents and associated processes have caused gradual global cooling. Around three million years ago when glaciers first appeared on northern continents, our planet's response to Milankovitch forcing - modest, periodic fluctuations in the distribution of sunlight -- started amplifying, growing into dramatic oscillations between prolonged Ice Ages and brief interglacial periods. The present happens to be one of those temperate interglacial periods which, if the geological record is a guide, will end any millennium now with us sliding back into an Ice Age. That inference disregards the sharp, man-induced increase in the atmospheric concentration of carbon dioxide over the past century.  

The geological record raises a number of important questions:

1. Will the current increase in the atmospheric concentration of carbon dioxide restore the warm world of three million years ago?
2. What processes introduced the remarkable changes that occurred at that time?
3. How did the coastal zones of southern Africa respond to the subsequent recurrent Ice Ages?
4. What was the impact on the evolution of hominids and Homo sapiens?
5. Can future global warming eliminate the current contrasts between the coasts of the Atlantic and Indian Oceans?
6. How will the ocean, especially the coastal systems adjust to global warming?

In the search for answers to these questions southern Africa has a number of unique advantages:

1. Southern Africa has some of the most useful high resolution archives of past climates (e.g. in coastal sediment and speleotherms.)
2. Those archives describe changing conditions in a great diversity of climate zones, on land and in the oceans.
3. In southern Africa studies of the evolution of hominids and, subsequently of Homo sapiens, have a long and distinguished tradition on which to build.

The research topics being pursued include the following:

The Milankovitch Cycles

The changes in the Earth's response to the precisely known Milankovitch forcing provide ideal tests for climate models. The cornerstone of the descriptions of that response has been the record derived from deep sea cores and ice cores. While these remain very important sources they need to be augmented by low latitude terrestrial records. Potentially such records are available in Africa, especially the lakes in eastern Africa, and the deserts of southern Africa. Research in this area has reached the stage where data, in addition to providing records of what had happened, can test hypotheses that explain the various phenomena. The modellers are in need of data that are tests for their theories and models.

Ocean and Terrestrial Biogeochemistry - Glacial phase atmospheric CO₂ drawdown must go into the oceans, especially the Southern Ocean. In the Southern Ocean biogeochemical processes are controlled by atmospheric forcing (winds) and micro nutrients, some of which are derived from ocean circulation and some directly from terrestrial sources.  Southern Africa is an upwind source of some of these critical nutrients.  This strong and recognized terrestrial - atmosphere - ocean link raises important question which may explain the past changes in climate state.

Ecosystem adaptive capacity -The ecosystems that strongly influence our climate - they are of central importance to the processes that give us water, crops and even our geological wealth -- are in turn dependent of our climate. Because palaeo observations are based, not on the climate itself, but rather on the consequences of the climate (for example evidence of reduced rainfall may manifest in changing plant community structure derived from pollen analysis), the approach provides a direct look at the "so what" of climate change. With a tightly controlled time dimension to environmental change one gets insight into the assimilative and adaptive capacity of ecosystems.

Extreme event dynamics - Extreme events are an important aspect of climate change. The severity and frequency of palaeo-extreme events through time often exceeds the realms of modern observations. Although extreme events are typically the result of extraordinary circumstances, it is possible to incorporate the dynamics into climate change models. In this area evidence for palaeo-extreme events such as large scale flooding will be integrated into appropriate models such as run-off models in order to establish the magnitude of the extreme event. Where the magnitude or frequencies of extreme events are sufficient threat to communities or ecosystems additional effort will be invested in predictive modelling.