In part two of our series ‘The Shaping of Africa’, we look at how climate has affected nature, landscape and people.
Log on to any Internet search engine, type in “Africa Climate” and you immediately tune in to an anguished buzz of concern about the impact of global warming on this most vulnerable of continents.
Faster than at any time in the last 10,000 years, the planet is heating up. Especially in the south and east, soils will be drier, wet seasons wetter, droughts longer. Harvests will become even less certain, woodland will recede, wildlife will dwindle. The potential impact on life is truly alarming.
But such changes are nothing new. Weather has constantly reshaped the land and the life it sustains. Even the arid Sahara once had a softer fac. Buried riverbeds, ancient rock carvings of elephant and pools of still-surviving crocodiles suggest that, here too, there once was water.
Now, in the southern Sahara, across a band so wide it almost spans the continent, the desert is again in retreat. In Burkina Faso some areas have greened so much that people who once fled in despair are returning. One report described a “spectacular” increase in vegetation, a 70 per cent leap in the production of grain and bushes and trees encroaching steadily onto the dunes. Alas, this localised shift in the rainfall pattern, supplemented by clever conservation practices, serves only to underline the fragility of rural economies and the awesome power of climate over human existence.
That same power shaped our very humanity. In an earlier period of global change the great tropical forests receded, driving our primate ancestors onto the plains where they discovered the survival advantage of an upright stance. Later, as further fluctuations of temperature killed off large animal populations, the bipedal apes became armed hunters. From their new lifestyle flowed the richer diet, anatomical changes and advanced toolmaking skills that made us distinctively human.
The key element in all of this, according to palaeontologist Yves Coppens, was the thrusting up of mountains on either side of the Great Rift Valley and their subsequent drying effect on the regional climate. Separated from the tree-dwellers in the moister west, Homo sapiens is the direct result of that new aridity.
It is always tempting to look upon Africa as the primal world, unchanged since we first emerged. But its face has never been constant. Not even the ancestral eastern savannahs are quite as they were. Until recently cattle, not game, roamed what are now vast national parks. Before the 1890s, when Bantu peoples across the continent saw their herds devastated by rinderpest disease, these ancient grasslands would have looked rather different, in terms of both flora and fauna. Another reminder, like global warming itself, that the boot is now on the other foot. Now man impacts on climate and on everything shaped by climate, such as vegetation, agriculture and landscape. The consequences, like those of war, are unforeseeable.
The difficulty, for scientist and subsistence farmer alike, lies in the number of variables in the equation. The continental climate map, with its horizontally layered zones, looks deceptively symmetrical and ordered. The land mass straddles the equator almost equidistantly, producing a neat slice of mild Mediterranean character at the top and bottom. Next, moving towards the centre, come wide swathes of desert, then sem-desert, grassy savannahs and finally, like a wad of lush lettuce at the heart of a multi-layered burger, green tropical forest.
These broad bands are determined largely by the trade winds. But their behaviour is, and always has been, fickle. Everything depends on shifts in the surrounding ocean temperature, on the atmospheric winds, on rogue effects such as the El Niño Southern Oscillation and on inputs from even wider afield. None of these is fully understood, though immense strides are being taken by the CLIVAR-Africa research programme. No doubt by the time they are finally grasped, a whole new set of factors will have emerged.
The only certainty, for the reassuringly “unchanged” face of this most ancient of continents, is ceaseless ongoing change.
By Len Rix