A frican ecosystems and biodiversity are biologically and ecologically unique, attract substantial tourism revenue, and provide significant ecosystem services at local, regional and global levels. It is projected that anthropogenic climate change is likely to have adverse impacts on African ecosystems and their biodiversity 1 , but projections of impacts based on a range of methodologies diverge widely. This is partly due to contrasting scenarios of future precipitation, but much more importantly due to critical differences between approaches to modelling biodiversity impacts and their assumptions. These differences relate to the extent to which different modelling approaches incorporate the effects of atmospheric CO 2 and disturbance (fire, mammal herbivory) on ecosystem structure and productivity 2,3 , and relative strengths in accounting for temperature-versus water-related controls on biodiversity. Projections of large declines in biodiversity under combined scenarios of climate and socioeconomic development 4,5 may not take these uncertainties into account. The most recent report by the IPCC on African vegetation change 1 reflects this well in stating with high confidence that "substantial uncertainties are inherent in these projections [future changes in terrestrial ecosystems] because vegetation across much of the continent is not deterministically driven by climate alone".These issues require urgent resolution, because there are significant and immediate implications for biodiversity risk assessments, and adaptation and mitigation responses relevant for policymakers and land managers. The evidence necessary to resolve these divergences is indicative but far from adequate, primarily because of a dire lack of empirical evidence and information on both climate and atmospheric CO 2 impacts on the structure and function of waterlimited and disturbance-dependent ecosystems in tropical and subtropical climates 6,7 .More than any other continent, Africa's ecosystems are water limited 8 and disturbance driven (by wildfire and mega-herbivores) 9 , with a high representation of C 4 grass-dominated ecosystems 10,11 . Palaeoecological changes in climate and atmospheric CO 2 since the Miocene have strongly shaped the vegetation, disturbance regimes and biodiversity of these ecosystems 12 . Because the continent straddles the tropics and subtropics in both hemispheres, an enormous area over which climatic conditions are conducive to vegetation flammability emerged during the late Miocene 13 . The Projections of ecosystem and biodiversity change for Africa under climate change diverge widely. More than other continents, Africa has disturbance-driven ecosystems that diversified under low Neogene CO 2 levels, in which flammable fire-dependent C 4 grasses suppress trees, and mega-herbivore action alters vegetation significantly. An important consequence is metastability of vegetation state, with rapid vegetation switches occurring, some driven by anthropogenic CO 2 -stimulated release of trees from disturbance control. Thes...