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Climate change

Serge Janicot
Catherine Aubertin
Martial Bernoux
et al.

Part 2. The impacts of climate change in the South

The impacts of climate change in the South

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Red mangrove and striated heron. Mangrove trees are central to an ecosystem that is biologically very rich and contributes to the stability of coastal zones.

Red mangrove and striated heron. Mangrove trees are central to an ecosystem that is biologically very rich and contributes to the stability of coastal zones.

© Dangles and F. Nowicki

1The Fifth Assessment Report published by IPCC confirms with increasing certitude the global reality of climate warming caused by rising greenhouse gas levels and the consequences for the environment and societies. In particular, it warns the international community once again of a general increase in temperature accompanied by a probable increase in the frequency and intensity of meteorological events such as droughts, cyclones and floods. While all natural and human systems are concerned, much uncertainty remains about the consequences of warming at the regional level.

2The realities of climate change vary according to the geographic situation and the type of ecosystem. While the average world increase in temperature has been +0.78 °C in a century, it is twice as great in arid environments and in particular in the Sahel. Regional responses to higher CO2 levels are even more contrasted when precipitation and extreme events are examined. The multidisciplinary work carried out by IRD on different types of tropical environment underlines the complexity of the processes involved and the multiplicity of determinants as each environment is subjected to different climate events (cyclones, droughts, floods, rising sea level, warming) and displays its own vulnerability and degree of exposure to the climate risks that affect it. These risks are often worsened in countries in the South by endemic poverty and the small control resources that can be mobilised.

3Ocean warming thus threatens the marine environment through redistribution of marine species, irreversible coral bleaching and a decrease in fisheries resources, with consequences for food security. More recently, scientists have discovered the ocean acidification phenomenon and are just beginning to assess the effect on marine ecosystems.

4Coastal systems are also subjected to the effects of ocean warming and acidification, together with the expected rise in sea level and coast erosion.

5The semi-arid regions, with a rainy season lasting for several months, are particularly sensitive to the rise in temperatures and change in the rainfall regime. These rapidly affect water and food resources.

6In highland regions, warming has consequences that are already clearly visible: the retreat of glaciers accompanied by changes in the hydrological regimes of drainage basins, water supply problems and also loss of biodiversity in these environments with the migration or disappearance of certain species.

7Humid tropical forests are threatened by increased risk of fires and the major rivers have experienced exceptional floods with frequently dramatic effects for transport, fishing, agriculture and habitats. Although the erosion of biodiversity seems les obvious than in other environments, it is nonetheless in progress.

8Urban environments are strongly affected and are suffering harmful sanitary effects (air pollution, heatwaves) that sometimes cause serious human losses as a result of the increasing number of extreme events. The rise in sea level with submersion and landslides will in time cause many development and safety problems in the large coastal cities.

9Using field observations and satellite images and climate, ecological, hydrological and agricultural modelling, Part 2 illustrates the processes operating and recent trends and also future projections should greenhouse gas emissions continue. Although the ‘signature’ of climate change has already been seen clearly in ocean and continental observations over the past 50 years, the risk of major disturbance of these systems will be all the more serious as the warming to come will be rapid and intense.

10One difficulty of interpreting changes in environments is that climate change is only one risk among others. In particular, human activities and population pressure often weigh more on environments and resources than climate change itself. This is the case in particular of mangrove ecosystems and coral reefs (Chapter 9) and freshwater fish resources (Chapter 12). It is very difficult to identify the influence of climate warming when it is combined with these other changes. For example, the risk of submersion depends as much on rising sea levels as on the urban development of coasts (Chapter 9).

11This section also illustrates the difficulties in observing and forecasting climate change; this affects natural and human systems in a very uneven manner. Certain cold ocean regions could benefit from the arrival of new marine species from the warmer zones in the south (Chapter 8). Whereas coastal areas can recover naturally from massive erosion (Chapter 9) and the vegetation can recover in the Sahel after decades of drought (Chapter 10), coastal cities will be fully exposed to the effects of climate change as vulnerability is acute there (Chapter 13).

12Finally, certain environments such as the oceans and forests that serve as carbon sinks can also amplify or regulate carbon dioxide concentrations and thus change the trajectory of climate warming.

13The specific features of each environment and the complex phenomena involved justify the regional, multidisciplinary approach used in Part 2. This also reflects IRD’s strategy of favouring integrated research on climate founded on multidisciplinary programmes conducted in various regions of the tropics.

Table des illustrations

Titre Red mangrove and striated heron. Mangrove trees are central to an ecosystem that is biologically very rich and contributes to the stability of coastal zones.
Crédits © Dangles and F. Nowicki
Fichier image/jpeg, 221k

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