The atmospheric concentration of carbon dioxide has increased by almost a third since 1750, and the present concentration has not been exceeded during the past 420,000 years and possibly during the past 20 million years. The atmospheric concentrations of those other important greenhouse gases, methane and nitrous oxide, have increased by more than 150 per cent and 17 per cent respectively since 1750. Chlorofluorocarbons, which are entirely artificial, have also been emitted, thereby contributing to the greenhouse effect, and although the Montreal Protocol and its amendments may control them, they have a long residence time in the atmosphere.
During the 20th century, the global average surface temperature increased by about 0.6C, causing such phenomena as glacier retreat and sea-level rise. The 1990s were the warmest decade on the instrumental record, and in the Northern Hemisphere the increase in temperature is likely to have been the largest of any century during the past 1,000 years.
The global average surface temperatures will have risen by 1.4C to 5.8C between 1990 and 2100, which represents a much larger rate of warming than that observed over the 20th century - and, based on palaeoclimatic data from ice cores and other sources, it is very likely to surpass anything experienced over the past 10,000 years. Northern high latitudes will probably warm more rapidly than the global average, possibly by more than 40 per cent.
Higher temperatures will in turn transform the behaviour of the atmospheric heat engine that drives the circulation of the air and the oceans, leading to changes in the nature, pattern and amount of precipitation. Some areas will become markedly drier. This is true of the Kalahari desert, where wholesale reactivation of dunes may occur by the century's end. Some areas will become wetter, and there is a continuing debate about how tropical cyclones will change in a warmer world. There are already signs that rainfall in many areas is becoming more intense, and this has grave implications for flood risk. Conversely, in some of the world's drylands, a combination of higher temperatures and less rain may cause stream flow to be reduced by more than 60 per cent.
Overall, most glaciers, especially in the tropical mountains, will wither away, permanently frozen subsoil (permafrost) will melt away from large stretches of the Northern Hemisphere, sea levels will threaten coastal lowland areas with inundation, and vegetation belts may migrate over hundreds of kilometres of latitude and some hundreds of metres by altitude.
Some important centres of biodiversity, such as the unique fynbos heath lands of South Africa's Cape, may shrink disastrously, while some coral reefs, particularly in warm seas such as the Caribbean, will succumb to increased bleaching as temperatures rise.
Our world is likely to change dramatically because of global warming, and these two books, both edited works by distinguished teams, seek to explore the implications for biodiversity and the environment of Africa respectively.
Climate Change and Biodiversity collects contributions from 66 writers into 24 chapters. Many of the contributors are well-known figures in the field.
The book covers a huge range of material through a mix of general chapters and case studies. The subject of climate change is treated at three timescales: the present, the past and the future, and the book closes with short sections on policy and conservation responses.
The theme is undoubtedly important, for climate change will cause habitat fragmentation. As human actions increasingly isolate species geographically, these fragmented communities of species will be rendered misplaced by climate change, and so will have to shift - something that in many cases will be made difficult because migrating species will find many obstacles in their paths, including factories, farms, roads and cities.
Some species and assemblages may find there is no suitable habitat to move to: the polar bear and musk ox may find that the requisite arctic habitat has gone; the Caribbean coral may find the water just too hot; and the mountain dweller may find that its habitat migrates up the peaks until there is nowhere left.
In his contribution, Brian Huntley suggests that lessons from the past indicate that "in many cases, if not perhaps in the majority, species will be unable to achieve the rates of range change required to maintain equilibrium with future climatic changes resulting from anthropogenic interference with the climate system". So, although palaeoecological studies have demonstrated that species and communities were remarkably resilient in the face of climate changes in the Pleistocene, this cannot give us too much hope with respect to the future because of the existing habitat fragmentation, degradation and biodiversity loss caused by humans.
Climate change also has evolutionary implications. Chris Thomas, another contributor, remarks: "Directly or indirectly, climate change is likely to dominate the evolutionary process over the next century or more. Species and populations that remain where they are will experience different climates and will live in biological communities with altered compositions.
Species that shift their distributions will undergo evolutionary changes as they move, and will experience new selection pressures as they enter new regions and encounter new species assemblages."
In addition, new environments may be established with no present analogue, not least because of there being unprecedented carbon dioxide concentrations in the atmosphere. A recurring theme is how well species will cope with temperatures that will exceed those of previous interglacial periods. In the Southern Hemisphere, for example, temperate ecosystems are already highly fragmented, and there are concerns about whether species will be able to survive and compete with alien species in modified landscapes.
Much modelling work is being done to develop scenarios of future biodiversity change; but this work, which is vital to future conservation and land-management strategies, is still in its infancy. It is plain that increasingly dynamic conservation strategies are required to deal with biodiversity loss resulting from climate change.
Conservationists have already lost the battle against habitat loss arising from non-climatic stressors in areas such as insular Southeast Asia, often because of a lack of resources or political will, but the war will be even tougher when it becomes necessary to change the scale of conservation from the current site-scale (protected areas) system to the landscape scale. New protected areas will need to be set up because many existing nature reserves will be in the wrong place, and landscape corridors (escape routes) will need to be established to provide connections between the current and future conservation areas. Above all, however, efforts have to be made to convince politicians that greenhouse gas emissions must be controlled.
This volume produces some of the arguments on which such a case can be based. It is a well-edited and coherent book with excellent chapter summaries to make the reader clear as to what is being argued. It is, of course, questionable whether it will be effective, for, as Paul Colinvaux recently suggested in Nature : "If the government of a great nation will not act to protect the livelihoods of its own citizens, it is unlikely to take political risks to defend a few animals and plants." Does the American Bush care about the African bush?
This brings me to Climate Change and Africa , which has 31 chapters and 70 contributors. It starts with the science (climate change, desertification, trace gases and atmospheric chemistry and so on), moves to sustainable energy development, mitigation and policy, considers vulnerability and adaptation, explores capacity building, then concludes with lessons to be learnt from the Montreal Protocol on ozone depletion.
Africa and Africans are at severe risk from climate change. The continent has vast tracts that are already dry and may get drier. It also has some very steep rainfall gradients, as in West Africa. Thus, quite small changes in the atmospheric circulation and in the position of the Intertropical Convergence Zone could potentially lead to rapid and substantial climate changes over quite short distances. Above all, however, most of its people are very poor and are highly dependent on farming and pastoralism for their livelihoods, activities that require reliable rainfall. They are thus peculiarly vulnerable to climate change but lack the economic resources to combat it.
With the important exception of biomass burning, Africans contribute relatively little to atmospheric compositional change, but they are likely to be disproportionately affected by it. The main weakness of this book is that it has relatively little to say about just how African environments are likely to react to the climate changes of coming decades. Future climate scenarios are discussed, and there is some material on future sea-level changes, but there are great swaths of material that have been largely ignored. For example, the Bodélé depression dust source in the central Sahara is a tipping point in earth-system science. How crucial is it to African climate? How will it be affected by climate change? The great relict dune fields of the Sahel, Sudan and the Kalahari may be reactivated in a warmer world. How extensive will this reactivation be? What is going to happen to all the lake basins of the continent? Are they likely to dry up or to be flooded? What is going to happen to the already limited water supplies of Africa? Can we say, for instance, how the Nile, the Zambezi and the Orange rivers are likely to respond? Will Africa be subjected to greater hurricane risk? What will happen to the glaciers and specialised montane environments of the high African mountains? How will the unique and wonderfully diverse fynbos biome be affected and might drought threaten the Congo rainforest in the way that has been proposed for parts of Amazonia?
This book's strengths lie in some of its longer chapters - many of the others are all too brief. Especially good are the chapters on Holocene climatic changes, future climate changes, biomass burning and sea level change. The book would have been more informative if it had contained fewer but more substantial chapters. Also, is there really a need for four forewords and four prefaces? Overall, I suspect that the book has too many authors who are either consultants or bureaucrats rather than true scholars. Worst of all, this work lacks passion. It is not persuasive. Its message is unclear and it lacks coherence. It is less successful than Climate Change and Biodiversity because of this.
How amazed the pioneers of environmental change science would be at the prominence of their field today. It has moved from being the preserve of eccentric geographers from the Fens, caricatured as nut cutlet-eating, sandal-wearing tree-huggers, into a field of wide interest and importance that goes way beyond academia.
Together, these two books provide a compelling assessment of the necessity to take global change seriously, in terms of biodiversity and in the welfare and environmental sustainability of a great continent. They show the value of interdisciplinary research, the large uncertainties that exist in our data and in our models, the complex linkages between future climate change and other human impacts on the environment, and the difficulty of making a convincing case that is sufficiently accessible to policymakers.
Andrew Goudie is master of St Cross College, Oxford, and author of The Human Impact on the Natural Environment , to be published in 2006.
Climate Change and Biodiversity
Editor - Thomas E. Lovejoy and Lee Hannah
Publisher - Yale University Press
Pages - 418
Price - £45.00
ISBN - 0 300 10425 1