9.4.5 Ecosystems
A range of impacts on terrestrial and aquatic ecosystems has been suggested under climate change (see, for example, Leemans and Eickhout, 2004), some of which are summarised in Table 9.1 (for further details see Chapter 4; Nkomo et al., 2006; Warren et al., 2006).
Table 9.1. Significant ecosystem responses estimated in relation to climate change in Africa. These estimations are based on a variety of scenarios (for further details on models used and impacts see Chapter 4, Section 4.4 and Table 4.1).
| Ecosystem impacts | Area affected | Scenario used and source |
|---|
| About 5,000 African plant species impacted: substantial reductions in areas of suitable climate for 81-97% of the 5,197 African plants examined, 25-42% lose all area by 2085. | Africa | HadCM3 for years 2025, 2055, 2085, plus other models – shifts in climate suitability examined (McClean et al., 2005) |
| Fynbos and succulent Karoo biomes: losses of between 51 and 61%. | South Africa | Projected losses by 2050, see details of scenarios (Midgley et al., 2002; see Chapter 4, Section 4.4, Table 4.1) |
| Critically endangered taxa (e.g. Proteaceae): losses increase, and up to 2% of the 227 taxa become extinct. | Low-lying coastal areas | 4 land use and 4 climate change scenarios (HadCM2 IS92aGGa) (Bomhard et al., 2005) |
| Losses of nyala and zebra: Kruger Park study estimates 66% of species lost. | Malawi South Africa (Kruger Park) | (Dixon et al., 2003) Hadley Centre Unified Model, no sulphates (Erasmus et al., 2002; see Chapter 4, Section 4.4.3) |
| Loss of bird species ranges: (restriction of movements). An estimated 6 species could lose substantial portions of their range. | Southern African bird species (Nama-Karoo area) | Projected losses of over 50% for some species by 2050 using the HadCM3 GCM with an A2 emissions scenario (Simmons et al., 2004; see Chapter 4, Section 4.4.8) |
| Sand-dune mobilisation: enhanced dune activity. | Southern Kalahari basin – northern South Africa, Angola and Zambia. For details in Sahel, see Section 9.6.2 and Chapter 4, Section 4.3. | Scenarios: HadCM3 GCM, SRES A2, B2 and A1fa, IS92a. By 2099 all dune fields shown to be highly dynamic (Thomas et al., 2005; see Chapter 4, Section 4.4.2) |
| Lake ecosystems, wetlands | Lake Tanganyika | Carbon isotope data show aquatic losses of about 20% with a 30% decrease in fish yields. It is estimated that climate change may further reduce lake productivity (O’Reilly et al., 2003; see Chapter 4, Section 4.4.8) |
| Grasslands | Complex impacts on grasslands inc-luding the role of fire (southern Africa) | See detailed discussion Chapter 4, Section 4.4.3 |
Mountain ecosystems appear to be undergoing significant observed changes (see Section 9.2.1.4), aspects of which are likely to be linked to complex climate-land interactions and which may continue under climate change (e.g., IPCC, 2007a). By 2020, for example, indications are that the ice cap on Mt. Kilimanjaro could disappear for the first time in 11,000 years (Thompson et al., 2002). Changes induced by climate change are also likely to result in species range shifts, as well as in changes in tree productivity, adding further stress to forest ecosystems (UNEP, 2004). Changes in other ecosystems, such as grasslands, are also likely (for more detail, see assessments by Muriuki et al., 2005; Levy, 2006).
Mangroves and coral reefs, the main coastal ecosystems in Africa, will probably be affected by climate change (see Chapter 4, Box 4.4; Chapter 6, Section 6.4.1, Box 6.1). Endangered species associated with these ecosystems, including manatees and marine turtles, could also be at risk, along with migratory birds (Government of Seychelles, 2000; Republic of Ghana, 2000; République Démocratique du Congo, 2000). Mangroves could also colonise coastal lagoons because of sea-level rise (République du Congo, 2001; Rocha et al., 2005).
The coral bleaching following the 1997/1998 extreme El Niño, as mentioned in Section 9.2.1, is an indication of the potential impact of climate change-induced ocean warming on coral reefs (Lough, 2000; Muhando, 2001; Obura, 2001); disappearance of low-lying corals and losses of biodiversity could also be expected (République de Djibouti, 2001; Payet and Obura, 2004). The proliferation of algae and dinoflagellates during these warming events could increase the number of people affected by toxins (such as ciguatera) due to the consumption of marine food sources (Union des Comores, 2002; see also Chapter 16, Section 16.4.5). In the long term, all these impacts will have negative effects on fisheries and tourism (see also Chapter 5, Box 5.4). In South Africa, changes in estuaries are expected mainly as a result of reductions in river runoff and the inundation of salt marshes following sea-level rise (Clark, 2006).
The species sensitivity of African mammals in 141 national parks in sub-Saharan Africa was assessed using two climate-change scenarios (SRES A2 and B2 emissions scenarios with the HadCM3 GCM, for 2050 and 2080), applying a simple IUCN Red List assessment of potential range loss (Thuiller et al., 2006). Assuming no migration of species, 10-15% of the species were projected to fall within the IUCN Critically Endangered or Extinct categories by 2050, increasing to 25-40% of species by 2080. Assuming unlimited species migration, the results were less extreme, with these proportions dropping to approximately 10-20% by 2080. Spatial patterns of loss and gain showed contrasting latitudinal patterns, with a westward range shift of species around the species-rich equatorial transition zone in central Africa, and an eastward shift in southern Africa; shifts which appear to be related mainly to the latitudinal aridity gradients across these ecological transition zones