Table Of ContentDevelopments 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
