Soils on A Warmer Earth: Effects of Expected Climate Change on Soil Processes, with Emphasis on the Tropics and Sub-Tropics, Proceedings of an International Workshop on Effects of Expected Climate Change on Soil Processes in the Tropics and Sub-tropics PDF
Preview Soils on A Warmer Earth: Effects of Expected Climate Change on Soil Processes, with Emphasis on the Tropics and Sub-Tropics, Proceedings of an International Workshop on Effects of Expected Climate Change on Soil Processes in the Tropics and Sub-tropics
Developments in Soil Science 20 SOILS ON A WARMER EARTH effects of expected climate change on soil processes, with emphasis on the tropics and sub-tropics Edited by H.W. SCHARPENSEEL Institute of Soil Science, University of Hamburg, Allende-Platz, 0-2000 Hamburg 13, F.R. Germany and M. SCHOMAKER and A. AYOUB UNEP, P.O. Box 30552, Nairobi, Kenya Proceedings of an International Workshop on Effects of Expected Climate Change on Soil Processes in the Tropics and Sub-tropics, 12-14 February 1990, Nairobi Organized by United Nations Environment Programme (UNEP) International Society of Soil Science (ISSS) Sponsored by (ISSS) United Nations Environment Programme (UNEP) UNEP International Society of Soil Science (ISSS) EC Technical Centre for Agriculture and Rural Development (CTA) ELSEVIER Amsterdam - Oxford - New York - Tokyo 1990 ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat 25 P.O. Box 211,1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY INC. 655, Avenue of the Americas New York, NY 10010, USA. ISBN 0-444-88838-1 0E lsevier Science Publishers B.V.. 1990 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B.V./ Physical Sciences & Engineering Division, P.O. Box 330,1000 AH Amsterdam, The Netherlands. Special regulations for readers in the USA. - This publication has been registered with the Co- pyright Clearance Center Inc. (CCC ), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the copyright owner, Elsevier Science Publishers B.V., unless otherwise specified. No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This issue is printed on acid-free paper. Printed in The Netherlands ix FOREWORDS The motivation for organizing the International Workshop ‘Effects of Expected Climate Change on Soil Processes in the Tropics and Subtropics” was threefold. Soil Science is heavily involved in the problems of trapped radiation in the atmosphere by greenhouse effect (GHE) promoting gases. The e€fect of soils on the GHE syndrome was analyzed in a preceding conference: the International Conference on Soils and the Greenhouse Effect, Wageningen, the Netherlands, August 1989, organized by the International Soil Reference and Information Centre (ERIC). An answer was needed regarding the effect of climate change on sustainable productivity of soils, with emphasis on tropical and subtropical regions. The confusing dispute in scientific and popular science journals regarding the predictions of effects of temperature and eustatic sea-level rise, as well as a wide array of possible advantages and disadvantages due to especially C02-rise, had to be thoroughly evaluated against the background of impacts on soil changes. A state of the art of predictive approaches, recognized by the majority of scientists, had to be elaborated. In this volume some 24 scientists contributed to such an evaluation and inventory, each in their own specific field. Though differences in opinion on assumptions, approaches and predictions still exist, these proceedings clearly bring the discussion a great step forward, and it is hoped that they will be of assistance to the soil science community in deciding on concepts for soil related core programmes of the forthcoming International Geosphere Biosphere Programme. The editors x Forewords What once were local incidents of environmental damage, confined to one area and region now involve the whole world. Concern on the global environment has indeed become more and more pressing. All people concentrate their attention to this matter, regardless of their wealth. The United Nations Congress, the Alsh Summit and the Tokyo Conference on Global Environment and Human Response Towards Sustainable Development in 1989, issued the statements that the human race may be making our planet uninhabitable. They are concerned about the rapid decrease in land which should be set aside for forests and other vegetation, essential for maintaining the balance of atmospheric gases, and about the increasing deterioration of soil, water and air, that support the continued existence of all life on the earth. These threatening developments call for an increased emphasis on studies specifically aimed at problems of global change. In a broader perspective the need to expand the role of soil scientist's approaches to global environmental and resources utilization is evident. May these proceedings become an important milestone, which will amongst others contribute to a fruitful discussion during the 14th International Society of Soil Science Congress and its symposium "Global Soil Changes Under Influence of a Changing Environment" (Kyoto, Japan, August 1990). Professor Y. Takai Vice-president, ISSS Fore words xi The theme of this book is a far reaching one and should attract great interest, both in industrialized as well as in less developed countries. Although the question of climate change and its effects on soil productivity is overshadowed by so many current events, it is almost certain that this subject will remain on the international agenda for the years to come; not only as science and research are concerned but also in relation to development policies, agricultural policies and others, especially since poor, rich, developed and developing countries are equally threatened by these problems. The Technical Centre for Agricultural and Rural Co-operation (CTA), provides ACP states with better access to information, research and innovations in the spheres of agricultural and rural development. CTA gives great attention to increasing agricultural production on a sustainable basis and CTA is prepared to strengthen and expand these activities in the years to come. Within this context the recommendations in these proceedings and the subsequent follow-up will be of great interest to us and we are certainly prepared to continue our collaboration in this respect with the United Nations Environment Programme (UNEP) and the International Society of Soil Science (ISS S). Dr. W. Treitz Deputy Director, CTA/ACP-EEC Lorn6 Convention xii Forewordr Each day, we are getting a clearer understanding of the growing pressures that threaten our planetary biosphere. Each day, pressures are mounting, due to demographic momentum and rising industrialization. Though uncertainties remain about the magnitude of climate change, scientific evidence confirms human activity has undoubtedly altered, and continues to alter, the atmosphere. While the principle greenhouse gas is carbon dioxide from fossil fuels, agricultural practices are having important impacts on possible changes in global climatic regimes. Recent studies suggest burning of savannahs for agriculture contributes three times more carbon dioxide per hectare to the atmosphere as does burning of tropical forests. Savannah clearing and increase in cattle and rice paddies are just three greenhouse gas sources from agriculture. Studies suggest soil processes involving inputs and outputs of water, gases, soluble salt and organic matter are likely to be influenced by global mean temperature increases. Such changes could in turn reduce land productivity, further threaten biodiversity, exacerbate soil loss and disrupt sediment budgets. Productive cropping areas could turn into deserts, while coastal storms could inundate or degrade fertile lands. Restoring the balance between the sources and the sinks of greenhouse gases will likely not be achieved solely through carbon emission reductions. Conserving existing carbon sinks (oceans, rainforests, grasslands, mangroves, coral reefs, etc.) and significantly increasing the productivity on degraded soils would be cost effective measures to achieve both environmental and economical sustainability. Massive reforestation, regrassing and amelioration of degraded lands are needed. A growing challenge to soil experts and agriculturalists is to produce more food for our growing world-wide population (currently already at 5.2 billion) from finite and shrinking productive lands. Of the total world-wide area of potential arable land, nearly half (about 1.5 billion ha) is already cultivated. There are very few virgin lands easy to exploit for additional food production. With these proceedings, a serious effort has been made to: 1) discuss latest knowledge on the expected impact of climate change on soil processes, with emphasis on the tropical and sub-tropical regions; 2) agree on recommendations for meaningful and useful future research and monitoring programmes; and 3) formulate policy responses to the expected impact in the form of preventive and adaptive measures. I hope that with these proceedings, we have moved forward to a better understanding of soil processes and their relationship to climate change. Mostafa K. Tolba Executive Director, UNEP ... Xlll PREFACE The Plan of Action for the implementation of the World Soils Policy was endorsed by UNEP’s Governing Council in 1984. The document identified the international action required to promote the sound use of land and soil resources. It also highlighted the need for internationally acceptable methods for assessing and monitoring the existing status and risk of soil degradation. The importance of ensuring that practices to prevent soil degradation, improve land productivity and reclaim degraded areas are appropriate to Iocal physical, economic, social and cultural conditions had been recognized in the document. At the same time, it is also recognized that serious gaps exist in knowledge of the extent, mechanisms and economic consequences of soil degradation as well as in knowledge of costeffective means for controlling erosion and other forms of land degradation. Consequently, there is an equally urgent need for a long term commitment by international organizations and Governments to support research on mechanisms and effects of soil degradation on the development for combatting soil erosion, as well as for the identification of critical areas and for a standardized assessment of soil resources and of the seriousness of soil degradation, through surveys and inventories. Methods are required which can reliably detect significant changes in those soil and land characteristics which directly or indirectly affect the quality and quantity of the land and its liability to produce food, fibre and timber. The manipulation of the pedosphcre by man is substantial and is likely to increase strongly until at least the year 2050, whcn the world population is expected to peak. This manipulation certainly has an impact on global climate and should be taken into account in connection with the increasing greenhouse effect on climate. The present status and future trends concerning the effects of soils and land cover on the fluxes of greenhouse gases, the surface energy balance and the water balance are discusscd in Bouwman (1990). The current publication explores and assesses the concept, the trends and impacts of the possible global warming on soil processes in the tropics and sub-tropics. Hierarchical research requirements and response stratcgies nccessary to meet the ncgative impacts of climate change on soils are also outlined. UNEP sees that the great task for the world community is therefore three fold: 1) to reduce greenhouse gascs; 2) to prepare for the impacts of global warming; and 3) to provide technical and financial assistance to developing countries so that their strive towards legitimate economic expansion is not hampered by measures addressing global warming. UNEP welcomes thc concern expressed on global warming at the highest levels. Thcse and other priorities, such as protection of land resources by combatting dcsertification and x iv Preface deforestation, have bcen constant pre-occupations of UNEP for well over a decade. The preparatory work for global conventions on climate change and biological diversity are but a few of the many actions of UNEP to safeguard our planet. A.T. Ayoub, Senior Programme Officer, UNEP xv CONCLUSIONS AND RECOMMENDATIONS OF THE INTERNATIONAL WORKSHOP ON THE EFFECTS OF EXPECTED CLIMATE CHANGE ON SOIL PROCESSES The workshop discussed how soils in specific ecosystems respond to changes of climate and the need for soil scientists to work with other disciplines. It also listed research priorities and discussed how the use and management of soil resources can mitigate climate change and at the same time adapt to it. ECOSYSTEM DYNAMICS, INTERACTIONS WITH THE ATMOSPHERE AND THEIR EFFECT ON SOIL AND LAND USE A scenario and some predictions We assumed: over a time span of about 50 years a gradual warming of the atmosphere of about 3°C with 2°C in tropics and 5°C in sub-polar areas; 10% increase of precipitation, a sea level rise of 50 cm, and an equilibrium world population of 10 billion; by about the year 2100 a doubling of the atmospheric C02 content. The results of geophysical, geochemical, and biogeochemical processes vary widely in current soil ecosystems. Within a decade changes of temperature and precipitation will influence soil temperature and moisture regimes, pH, base saturation, fertility status, surface litter and biological activity, and the presence of salic and fluvic soil properties where appropriate. Over a period of several decades changes of climate are manifested in soils through the depth and kind of humus in the topsoil, relative fertility, erosion, and in peatiness, swell-shrink features, degree of bleaching and calcareoumess. We believe that soil ecosystem responses to changes in land cover and climate differ mainly due to different degrees in sensitivity of soils to disturbance and modification. It is recognized that there are likely to be very large regional and local variations in the manifestation of warmer earth conditions. Nevertheless the following general statements can be made for some major ecosystems. In a Tropical Rain Forest ecosystem (hot, humid) one might expect increases of forest growth, nutrient cycling, and mineral weathering. Ferralsols are common in such biomes and with more percolation through the soil we would expect a decline of the fertility status, slight decreases of pH and base saturation, more litter production but also more biological activity with little change in humus content in the topsoil. Additional Weathering of minerals would occur, however, due to the great thickness of many saprolites there would be little change in relative fertility over time. Although soil processes would respond to the changes of climate and vegetation the overall impact would be minimal compared to the present ecosystcm. Thcse kinds of soils have low sensitivity to the assumed xvi Conclusions and recommendarions climatic changes. In a Steppe or Grassland ecosystem (warm, semiarid) the increase of precipitation would increase biomass production and movement of water through and on the soil. In such ecosystems, Chernozemic soils are common; they are moisture sensitive and the humus content in the topsoil would increase, carbonates and other soluble salts would leach deeper and salinization might occur in adjacent lower areas. Soil pH and base saturation would decrease slightly but the nutrient supply would remain high. Increased erosion would occur on slopes where vegetation would become stressed. In a subpolar Boreal Forest ecosystem (cold, subhumid) we would expect an increase of biopmductivity and biogeochemical cycling. For the dominant soils in this ecosystem, Podzols, the humus content, base saturation, relative fertility status and pH would become higher. The litter and liistic horizon, if any, would become thinner, leaching would tend to intensify, and the spodic horizon would likely become thicker. The vegetative cover would minimize erosion of the soil. The soil processes in this ecosystem are fairly sensitive to the assumed climate changes, especially temperature. We conclude that the changes in soil processes will be substantially more pronounced in cold and temperate regions than in the tropics because the soils outside the tropics are more temperature sensitive and the temperature changes are expected to be greater there. As one approaches the transitional zones between ecosystems ("ecotones") it is more difficult to make general predictions about soil changes because of the strong interactions of climate and biota that often occur in such zones. In coastal swampy areas and tropical mountains a global warming can have dramatic effects on the ecosystems. Rising sea levels would generate a host of events such as flooding, salinization, and new erosion and sedimentation patterns that would affect many soil ecosystems. In mountainous areas the ecological zones respond to elevation, thus a warming would push the climatic belts up the mountains, creating new conditions. The essential contribution of soil science to climate change studies The impact of climate change will be extremely diverse and difficult to predict. The consequence for soils and their associated vegetation will be even more complex, and will have the most wide ranging and diverse consequences for agriculture, forestry, ecology, conservation, and all forms of land use. Progress in understanding and pedicting these effects can only be made by multidisciplinary studies. Soil science forms an essential component of such work. Soil is the basis for plant growth, and the full effects of climate change will be mediated by complex interaction between the two. There will also be direct effects of increase in atmospheric C02.A t the highest level, full scale ecosystem studies are essential to understand changes resulting from broad shifts of vegetation bands and biomes. Major modeling programmes will be needed at
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