Can we crop carbon a case study in north south climate mitigation

Can We Crop Carbon?
A case study in North-South
climate mitigation

Mike Robbins

A thesis submitted to the School of Development Studies, University of
East Anglia, in partial fulfilment of the requirements for the degree of
Doctor of Philosophy.

October 2007

© This copy of the thesis has been supplied on condition that anyone
who consults it is understood to recognise that its copyright rests with the
author and that no quotation from the thesis, nor any information derived
therefrom, may be published without the author's prior, written consent.


ABSTRACT
Scientific evidence suggests that the climate is changing through anthropogenic
emission of carbon dioxide and other gases. To mitigate this, a growing number of
mechanisms aim to provide a market for the trading of emissions reductions, and
international development assistance also often includes mitigation as an objective.
This thesis examines the hypothesis that, through such initiatives, agriculture in the
developing world could increase the terrestrial carbon sink, and that farmers could
derive benefit from the carbon’s value. In examining this hypothesis, it also seeks to
illuminate North-South aspects of international climate negotiations.
The on-farm carbon pools in the developing world have so far been excluded from
the Kyoto mechanisms. But the substantial potential of agriculture to act as both
carbon source and sink means that it should be considered for inclusion after the end
of the current Kyoto reporting period in 2012. However, there will be difficult

marketing and methodological challenges. This thesis considers how these can be
overcome. Unilateral project funding can address marketing issues, while new
technologies can assist in monitoring and verification. A pragmatic approach is
required to additionality, while baselines might be modelled and then verified with
control plots during implementation. Finally, a field study in the Brazilian Atlantic
Forest sought to match “carbon-friendly” interventions to farmers’ own priorities and
constraints, so that any sinks created would be maintained by them after any project.
Some lessons can be drawn for the international climate regime in general.
Permanence of sinks ultimately demands that countries have an incentive to maintain
their carbon stocks, and this should be done through tradeable emissions quotas for
every country. Also, refinement of the necessary methodologies will require specific
biophysical research, suggesting that climate change may call for more traditional and
specialized science.

2


Table of Contents
List of figures
List of tables
List of boxes
Acknowledgements
A note on measurements
Checmical formulae used
List of acronyms

5
6
6
7

8
8
9

1

Introduction

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2

Climate change and agriculture
2.1
Anthropogenic climate change
2.1.2 What climate change will do
2.1.3 The sceptics
2.1.4 The earth breathes out
2.2
Agriculture and climate change
2.2.1 SOM and its dynamic nature
2.2.2 Soil C: how much, where, and how much can
be sequestered?
2.2.3 How carbon can be sequestered in agriculture
2.3
Chapter summary

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26
28
29
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40
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3

Do we know what we know?
3.1
The postmodern attack on science
3.2
Science, policy and political ecology
3.2.1 Political ecology: Power and perception
3.3
The challenge of induction
3.4
Chapter summary

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46
49
51
52
54

4

Three carbon questions
4.1
The new Physiocrats
4.1.1 Costing carbon: Shadow pricing?
4.1.2 Costing carbon: Using the market
4.2
A price for everything?
4.3
Is there a market?
4.3.1 What now for the climate regime?
4.3.2 Flexible instruments, fungible carbon
4.4
Chapter summary

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61
62
65
71
72
83

5

Carbon, money and agriculture
5.1
Who would invest?
5.2

Additionality and baselines
5.3
Leakage
5.4
Permanence
5.5
Monitoring and verification
5.5.1 From sampling to modelling
5.5.3 Alternative sampling methods for ground truthing
5.5.4 Organizational aspects of monitoring

3

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105
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5.7

6

7

8

Chapter summary

110

A case study I: The Atlantic Forest biome
6.1
The Atlantic Forest
6.1.1 The decision to despoil, 1500-1823
6.1.2 Coffee
6.1.3 After coffee, cattle
6.2
Potential for carbon sequestration in the biome
6.3
Case study locations: Noroeste Fluminense
and Zona da Mata
6.3.1 Noroeste Fluminense
6.3.2 Minas Gerais: The Zona da Mata
6.4
A field survey
6.4.1 A methodology for assessing options
6.4.2 The interviews
6.5
Chapter summary
A case study II: Results
7.1
The sample and farming system
7.2
The sample in context and S.E. Brazil

7.2.1 Status of farmers
7.2.2 Farm size
7.3
Farmers’ responses
7.3.1 Constraints faced by farmers
7.3.2 Constraints faced and implications for carbon sinks
7.4
Rating the practices
7.4.1 Pasture improvement
7.4.2 Inorganic fertilizer
7.4.3 Organic agriculture, green manure and pigeonpea
7.4.4 Leguminous tree species
7.4.5 Conservation tillage and rotations
7.4.6 Managing the slope: Contour planting and
vegetative strips
7.4.7 Fruit trees
7.5
Discussion
7.5.1 Agricultural ideologies: A barrier to adoption?
7.5.2 Internalizing environmental costs: Who should do it?
7.6
Chapter summary
Conclusions
8.1
Can sinks in developing-country agriculture
mitigate emissions?
8.2
What has been learned about climate-change mitigation?

References

Annex 1:

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Questionnaire used for farmer interviews

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280


List of figures
Figure 2.1
Figure 2.2
Figure 4.1
Figure 4.2
Figure 5.1
Figure 6.1
Figure 7.1
Figure 7.2
Figure 7.3
Figure 7.4
Figure 7.5
Figure 7.6

Figure 7.7
Figure 7.8
Figure 7.9
Figure 7.10
Figure 7.11
Figure 7.12
Figure 7.13
Figure 7.14
Figure 7.15
Figure 7.16
Figure 7.17
Figure 7.18
Figure 7.19
Figure 7.20
Figure 7.21
Figure 7.22
Figure 7.23
Figure 7.24
Figure 7.25
Figure 7.26
Figure 7.27
Figure 7.28
Figure 7.29
Figure 7.30
Figure 7.31

Global terrestrial carbon stocks
Global net primary productivity (NPP)
Climate-change negations: A timeline
Growth in allowance- and project-based

transactions, 2004-2006
Funding and benefit flows from environmental
services projects in agriculture
Destruction of the Atlantic Forest, 1500-1990
Locations of farmer interviews
Status of sample compared with family farms in
South-East Brazil and Brazil
Status of sample compared with family farms in
South-East Brazil and region/microregion
Farm size, sample compared with South-East Brazil
Farm size, samples for Noroeste Fluminense (Rio de Janeiro)
and Zona da Mata (Minas Gerais) compared with States
Farm size, samples compared with Noroeste Fluminense
and Ubá
Farmers’ rating of main constraints to farm production
Persons employed in agriculture in Minas Gerais and Rio de
Janeiro States, 1970-1996
Pasture as a percentage of agricultural area at sample,
local and State levels
Farmers’ views on pasture improvement by
ploughing/seeding with Brachiaria spp.
Farmers’ ratings of constraints to pasture improvement
by ploughing/seeding with Brachiaria spp.
Farmers’ views on inorganic fertilizer
Farmers’ ratings of constraints to using inorganic fertilizer
Farmers’ views on organic agriculture
Farmers’ ratings of constraints to using organic agriculture
Farmers’ ratings of constraints to using organic agriculture,
Noroeste Fluminense and Zona da Mata
Farmers’ views on green manure

Farmers’ ratings of constraints to using green manure
Farmers’ views on pigeonpea
Farmers’ ratings of constraints to using pigeonpea
Farmers’ views on leguminous trees
Farmers’ ratings of constraints to using leguminous trees
Farmers’ views on conservation tillage (CT)
Farmers’ ratings of constraints to conservation tillage (CT)
Farmers’ views on sustainable rotations
Farmers’ ratings of constraints to sustainable rotations
Farmers’ ratings of sustainable rotations, Noroeste
Fluminense and Zona da Mata
Farmers’ ratings of constraints to using sustainable rotations,
Noroeste Fluminense and Zona da Mata
Farmers’ views on contour planting
Farmers’ ratings of constraints to using contour planting
Farmers’ ratings of constraints to using contour

5

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Figure 7.32
Figure 7.33
Figure 7.34

Figure 7.35
Figure 7.36
Figure 7.37
Figure 7.38
Figure 7.39
Figure 7.40

planting, Noroeste Fluminense and Zona da Mata
Farmers’ views on vegetative strips
Farmers’ ratings of constraints to using vegetative strips
Farmers’ ratings of constraints to using vegetative strips,
Noroeste Fluminense and Zona da Mata
Farmers’ views on fruit trees
Farmers’ ratings of constraints to growing fruit trees
Farmers’ ratings of constraints to growing fruit trees,
Noroeste Fluminense and Zona da Mata
Farmers’ willingness to adopt (Would like to use/use more)
Mean ratings to constraints, all practices
Mean ratings to constraints, all practices, disaggregated

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List of tables
Table 2.1
Table 2.2
Table 2.3
Table 2.4
Table 6.1
Table 6.2
Table 6.3
Table 6.4
Table 6.5
Table 6.6
Table 7.1
Table 7.2

Potential for agricultural carbon sequestration in
the developing world, 2003-2013
Carbon sequestration potential (tC ha/yr) in four
agricultural systems under different levels of management
Agriculture’s contribution to global greenhouse-gas emissions
C sequestration potential of strategies for arable land
Species, threatened species and endemism in Brazil’s
Atlantic Forest
Land-use change and soil carbon stocks in the Atlantic
Forest biome under a realistic land-use change scenario
Key characteristics of fieldwork locations
Farmers’ reasons for non-adoption of soil
conservation technologies
Questionnaire for farmers’ ratings of carbon-friendly practices
Questionnaire for farmers’ ratings of constraints to adoption

of carbon-friendly practices
State- and GEF-funded components for rehabilitation of
degraded land, Rio Rural project
Growth and decline in economically active rural population
by category, Brazil, 1981-1999

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38
41
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121
132
135
139
142
232
241

List of boxes
Box 1
Box 2
Box 3
Box 4
Box 5
Box 6
Box 7

A flexible farmer
A farmer questions fertilizer

Important to invest in soil
A place to try the trees?
Small-farm sustainability
Coping with slopes
Going for guava

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6


ACKNOWLEDGEMENTS
Many people have assisted or influenced production of this thesis, the more so because its
origins go back many years. It would be impossible to thank them all properly, but I will try.
I must emphasize that they are not responsible for its content and would not necessarily
endorse its conclusions.
My supervisors, John McDonagh and Kate Brown, have been endlessly supportive, have
waded through mountains of chapter drafts without complaint and have made many useful
suggestions. I have been fortunate in that I have supervisors who between them cover a range
of biophysical and social science, and hope that this has helped me to view climate change
and agriculture from multiple perspectives. Other members of the faculty of the School of
Development Studies at UEA have also provided inspiration and support; in particular, Piers
Blaikie and Michael Stocking have encouraged me to think about soil erosion, while Jock
Cameron, Richard Palmer-Jones and Ken Cole have encouraged me to think. Bruce

Lankford, currently Head of School, has been a very positive influence. Shawn McGuire gave
very useful advice on biodiversity when I was working on a discussion paper for GEF in
2004. I have also had much encouragement and support, practical and otherwise, from the
faculty staff, especially Liz Gibson, Steph Simpson and Jessica Thimbleby.
Outside UEA, the roots of this thesis lie in a conversation about agriculture and climate
change with John Ryan, soil scientist at ICARDA in Syria, in the 1990s. And its approach
owes much to Michael Zoebisch, whose work and views on farmers and their environment
have very strongly influenced mine. His encouragement when I started to think about these
issues was invaluable. Many other staff at ICARDA also helped to form the way I think, as
did those with whom I worked in the Ministry of Renewable Natural Resources in Bhutan. I
also learned much from my colleagues at FAO in 2001-2002; in particular, I would like to
thank Jose Benites and Theodor Friedrich for discussions on reduced tillage and its
implications.
Warm thanks must go to a number of people Brazil, in particular Bob Boddey and Segundo
Urquiaga; there is no question of my work there having been possible without them. Thanks
too to Phil and Merci Chalk for encouragement and hospitality. Ricardo and Teresa Peixoto
provided invaluable advice and support. Eli de Jesus and Leila M. do Valle played a key part
in the field survey. Ednaldo da Silva Aráujo provided crucial advice and introductions on the
first field trip. Others whose time and/or encouragement was helpful include (in no particular
order) Claudia Jantalia, Antonio da Silva Viana, Gilmar Martins de Souza, Samuel de
Colares, Helga Restum Hissa, Nelson Teixeira Alves Filho, Peter May, Samuel de Colares,
João Batista Duarte Alvarez Viero, Marc Antonio Lopes, Jorge Luis Martin Soares, Marcos
Gonỗalves e Gonỗalves and Gilberto da Costa Reis. None of them are in any way responsible
for anything I have written about Brazil.
I would also like to thank those who gave me time and advice on two trips to WashinPgon
DC, in 2003 and 2005. On both trips, I had long and informative talks with Ian Noble and I
am grateful for his time. Others with whom discussions were helpful include Jonathan
Pershing, Per Ryden and Aáron Zazueta. I am also grateful to all those who attended the
seminar in March 2005 to review the GEF-STAP discussion paper that I prepared with Tim
Williams in the winter of 2004-2005, especially Chris Reij and Jeremy Sandford. Habiba

Gitay, Guadalupe Duron, and Tim himself gave great support at that event. However,
especially warm thanks are due to Scott Christensen and Andrea Pape-Christensen for their
hospitality and kindness on both those trips.

7


Last but not least, one’s friends are the environment in which a thesis is written. Sylvie
Koestlé, Marta Einarsdóttir, Patricia Almaguer-Kalixto, Neil Monk, Elaine Sherriffs, Emily
Boyd, Dan Coppard and Anna Allen have been especially supportive at various times. I
would also like to warmly acknowledge the company and encouragement of, among others,
Henry Alhassan, Johanna Wolf, Natasha Grist, Marisa Goulden, Jonathan Cate, Liz
Westaway, Laurence Mathieu, Tatiana Burmensky. Suzanty Sitorus, Samy Hotimsky, Esteve
Corbera Elizalde, Alejandra Trejo Nieto, Sirkku Juhola, Nadine Renaudeau d’Arc, Marie
Badjeck, Rocio Suarez, Sue Harris, Johnny Marsh, Alex Grimmer, Denis Hellebrandt da
Silva, Baruch Ramirez-Rodriguez, Piet van der Poel, Oscar-Salvador Alvarez-Macotela,
Hemant Ojha, Helen Heaney, Joe Hill, Lawrie Hallett, Matt Livermore, Bertha Cartas, Camy
Adelle, Mike Karlin, Suraje Dessai, Dolf te Lintelo, Fabiola Lopez Gomez, Louisa Evans,
Belina Garcia-Fajardo, Lan Anh Hoang, Joel Busher, Katharine Vincent, Lorena IbarguenTinley, Andrew Scanlon, Catherine Ball and Barry Ferguson.
Most are my fellow-students. Many are from overseas, especially from Mexico; I would like
to thank them for coming to study in my country, and hope that they have never regretted it.

A note on measurements
Because the study of agriculture in relation to climate mitigation is fairly new, there is some
confusion regarding units. 1 Pg (petagram) C is equivalent to 1015 g – that is, 1,000 million
metric tons; also much used for this in the literature is a gigaton (Gt), but to reduce confusion,
Pg has been used throughout, even where Gt was used in the original of a cited passage. Tons
are metric tons in all cases. Also used is a Tg, or teragram, of C (1012 g), 1,000,000 tons; and
Mg, or million grammes – in effect, a ton. Where a ton of soil carbon is mentioned, this
indicates a ton of solid matter; once mineralized, this is quivalent to 3.66 tons of carbon

dioxide (CO2 ). In this thesis, a ton of carbon is a ton of solid matter, and a ton of CO2 is
referred to as CO2e – that is, CO2 equivalent.
Chemical formulae used
C
CH4
CO2
CO2e
N
NO2

Carbon
Methane
Carbon Dioxide
Greenhouse Gases expressed as their equivalent to CO2 in radiative forcing potential
Nitrogen
Nitrogen Dioxide

8


ACRONYMS
AI
AIJ
BBC
BNF
BP
C&C
CARB
CBD
CCX

CDF
CDM
CEIVAP
CER
CGIAR
COP
CSE
CTIC
CV
DNA
DOE
EB
EMATER
EMBRAPA
ER
EU ETS
EU
EUA
FACE
FAO
FFW
FDI
FEBRAPDP
GCM
GDP
GEF
GHG
GNP
GPG
GPS

IADB
IBGE
ICARDA
ICSU
IFOAM
IFPRI
INCRA
INS
IPCC

Artificial Insemination
Activities Implemented Jointly
British Broadcasting Corporation
Biological Nitrogen Fixation
British Petroleum
Contraction and Convergence
California Air Resources Board
Convention on Biodiversity
Chicago Climate Exchange
Clean Development Fund
Clean Development Mechanism
Comitê para a Integracão da Bacia Hidrografíca do Rio Paraíba do Sul
Certified Emissions Reduction
Consultative Group on International Agricultural Research
Conference of the Parties
Centre for Science and the Environment
Conservation Tillage Information Center
Coefficient of Variation
Designated National Authority
Designated Operational Entity

Executive Board
Empresa de Assistência Técnica e Extensão Rural
Empresa Brasileira de Pesquisa Agropecuária
Emissions Reduction
European Union Emissions Trading Scheme
European Union
European Union Allowance
Free-Air CO2 Enrichment
Food and Agriculture Organization
Food-for-Work
Foreign Direct Investment
Federacão Brasileira de Plantio Direto na Palha
General Circulation Model
Gross Domestic Product
Global Environment Facility
Greenhouse Gas
Gross National Product
Global Public Good
Geographic Positioning System
Inter-American Development Bank
Instituto Brasileiro de Geografia e Estatística
International Center for Agricultural Research in the Dry Areas
International Council of Scientific Unions
International Federation of Organic Agriculture Movements
International Food Policy Research Institute
Instituto Nacional de Colonizaỗóo e Reforma Agrỏria
Inelastic Neutron Scattering
Intergovernmental Panel on Climate Change

9

ISWC
JI
LDC
LIBS
LULUCF
MRT
MST
NGO
NIRS
NPP
ODA
PES
PRONAF
RGGI
RUSLE
SLM
SOC
SOCRATES
SOM
SRES
SWC
TAR
T-CER
TDR
TERI
UK ETS
UNCED
UNEP

UNFCCC
USFS
VER
WFP
WMO
WRI
WUE
WWF
WOCAT

Indigenous Soil and Water Conservation in Africa
Joint Implementation
Least-Developed Countries
Laser-Induced Breakdown Spectroscopy
Land-Use, Land-Use Change and Forestry
Mean Residence Time
Movimento dos Trabalhadores Rurais Sem Terra
Non-Governmental Organization
Near Infrared Reflectance Spectroscopy
Net Primary Productivity
Official Development Assistance
Payment for Ecosystem Services
Programa Nacional de Fortalecimento da Agricultura Familiar
Regional Greenhouse Gas Initiative
Revised Universal Soil Loss Equation
Sustainable Land Management
Soil Organic Carbon
Soil Organic Carbon Reserves And Transformations in agro-EcoSystems
Soil Organic Matter
Special Report on Emissions Scenarios

Soil and Water Conservation
Third Assessment Report
Temporary Certified Emissions Reduction
Time Domain Reflectometry
Tata Energy Research Institute
United Kingdom Emissions Trading Scheme
United Nations Conference on Environment and Development
United Nations Environment Programme
United Nations Framework Convention on Climate Change
United States Forest Service
Verified Emissions Reduction
World Food Programme
World Meteorological Organization
World Resources Institute
Water-Use Efficiency
World-Wide Fund for Nature
World Overview of Conservation Approaches and Technologies

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1

Introduction
It is reasonable to assume that the dry margins of
semiarid lands contracted or expanded according to
climatic variations. But to propose that civilization
was chased from Babylon to London by a creeping
drought is not reasonable. The evidence for climate as
a destroyer of civilization is vague or nonexistent; the

evidence of soil erosion is there for all to see.
Carter and Dale, Topsoil and Civilization (1955)

S

cientific evidence suggests that the climate is changing due to human activity.
International negotiations to stop or reverse this have given rise to a system of

incentives for activities to mitigate emissions of greenhouse gases (GHGs). This thesis
reviews the hypothesis that farmers in the developing world might benefit from such
incentives by increasing carbon sinks. There are two basic research questions: First, is it
possible to mitigate climate change using such sinks? And second, in answering that
question, what can be learned about international climate negotiations, and the mitigation of
climate change in general?

There is a clear scientific rationale for considering agricultural sinks as a mitigation strategy.
CO2 emissions are – along with emissions of other gases – fuelling climate change. Sinks are
carbon pools, the contents of which are not adding to the atmospheric carbon pool because
they are held elsewhere. The size and nature of sinks is highly variable; forests are the bestknown but much carbon is also held in aquatic ecosystems, transported there by soil erosion,
while the oceans absorb a considerable amount of carbon dioxide – and undersea formation
of limestone is composed partly of carbon. Other carbon deposits include fossil fuels such as
oil and coal, formed over millennia from plant material. The stability of these sinks clearly
varies. Fossil fuels are stable until disturbed by human agency. But forests are subject both to
this and to natural fires.

The soil organic carbon pool is also subject to disturbance both by human activity and natural
processes, and its size is significant: 1,550 Pg ((Follett, 2001: 78-89), or roughly twice the
atmospheric carbon pool, which is 770 Pg (Lal, 2002: 353). Soil carbon can be converted to
CO2 through land-use change, ploughing and erosive processes that are mainly connected to

11


agriculture, which has therefore caused huge losses to the atmospheric pool ever since it
began in settled form about 8,000 years ago. How much is arguable; Lal (2004: 1623) reports
that estimates vary from 44 Pg to 537 Pg, but that they typically range from 55 Pg to 78 Pg.

However, there is widespread acknowledgement that agriculture can, at least in theory,
recover much of this. In 1998 nearly 100 North American scientists and agriculture-industry
figures met at St Michaels, Maryland to discuss the potential. In his summary of the
workshop, Rosenberg (1999: 1) reports it found that:

…[R]eductions in atmospheric carbon content can be achieved by largescale application of tried-and-true land management practices such as
reduced tillage; increased use of rotational crops such as alfalfa, clover
and soybeans; and by an efficient return of animal wastes to the soil.
Forests and grasslands afford additional capacity for carbon sequestration
when established on former croplands. Programs to further soil carbon
sequestration will provide ancillary benefits including improvements in
soil fertility, water holding capacity, and tilth, and reductions in wind and
water erosion (Rosenberg, 1999: 1).
Lal and Bruce (1999: 178), who estimate the historic loss at 55 Pg C, believe that as much as
75% might be recoverable through the sequestration of CO2 into the soil – that is, its
conversion into organic carbon, contained in plant material, through photosynthesis. FAO
(2001a: 61) suggests 23-44 Pg C in agricultural soils over the next 50 years; this implies that
agriculture can be of comparable significance to forests, the global sequestration potential of
which has been estimated at 60-87 Pg C (ibid.). This sequestered carbon can to some extent
be converted into soil organic matter (SOM) through (for example) the decomposition of root
systems and the incorporation of crop residues. This in turn can have positive inputs to
productivity, soil health and the sustainability of agriculture.

Although much of the potential lies in the developed world, increasing SOM could have
particular significance in regions where, for economic reasons, farming must be pursued in
fragile ecosystems; many of these are in poorer countries where low organic matter limits
productivity and resistance to erosive processes. So sequestration of carbon in agriculture can
both slow climate change, and benefit the rural poor. Meanwhile, the development of carbontrading instruments means that the carbon may have cash value, and this might be used to
fund initiatives to increase soil carbon. Despite this, agricultural sinks are currently excluded
from the Clean Development Mechanism (CDM) of the Kyoto Protocol, and it is by no
means assured that they will be eligible for Kyoto Phase II, should such an agreement come

12


into force after the current agreement expires in 2012.

This is despite agricultural sinks appearing to be a true “win-win” strategy with positive
implications for both climate-change mitigation and poverty alleviation. However, there are
pitfalls.

These became much clearer to me while I was studying for a Masters in Development Studies
at the University of East Anglia in 2002-2003, and chose agricultural sinks as my dissertation
subject. The main conclusions, briefly stated, were that the agronomic practices required to
sequester carbon were those already advocated for soil conservation and that these had a
difficult history in agricultural development. Linking these practices to carbon funding, as
well as soil conservation, would not automatically eliminate these difficulties. Moreover the
“history” of soil conservation, although well-known to agronomists, might not be understood
by those who initiated sequestration projects on behalf of multinational institutions. The
dissertation argued that there was therefore a need for a multidisciplinary approach to sinks.
It also highlighted the severe practical problems of monitoring and measurement, the
constraints to trading with resource-poor farmers, and the relationship between the way
farmers use organic matter and the broader economy in which they function.

However, it was not possible to do justice to the subject in a document of 12,000 words. In
particular, it identified the constraints to agricultural sinks in the developing world but
suggested few remedies for them. This thesis is different in four key ways. First, its greater
lenPgh permits deeper analysis. Second, it considers ways in which constraints to agricultural
sinks might be dealt with, including difficult areas such as additionality, baselines and
permanence. Third, it includes a case study that attempts analysis of a given biome to see
how agriculture might sequester carbon there.

Fourth – and this aspect evolved during the writing of the thesis – there is an attempt not
simply to consider agricultural sinks, but to see what that exercise might tell us about climate
mitigation, and the world climate regime, in general. If there are constraints to implementing
a funded sinks model, are they applicable to other areas of climate mitigation besides
agriculture? Some of the problems around additionality and permanence, in particular,
suggest that they are, and that lessons might be drawn for the post-Kyoto regime – the shape
of which is still unknown, although it is only five years in the future. There are thus two main
research questions, not one; not just whether agricultural sinks in the developing world are

13


practicable, but also what we can learn about the world climate-change regime in answering
that first question. So this thesis is both an examination of agricultural sinks and, to some
extent, a case study on North-South relationships in the context of climate-change mitigation.

The first question subdivides into several secondary research questions:

1)

How good is the evidence for anthropogenic climate change? It is widely accepted,

but is a fundamental assumption of the thesis, so should be examined at least briefly.

2)

Can agriculture do anything significant to mitigate it?

3)

How reliable is science in areas such as climate change? Is it fact, or a series of
reasonable assumptions? If there are very great uncertainties, care should be taken
before subjecting farmers to change.

4)

Can carbon really be priced, bought and sold, and if so, is there a market for it?

5)

Is it ethical to mitigate developed-country emissions through climate mitigation in
developing countries?

6)

Can agricultural sinks realize the value of carbon, by fitting into a trading regime or
through some other funding mechanism?

7)

What might be learned from a case study on sinks’ potential in agriculture in a given
area?

First of all, is climate change taking place? If it is not, agriculture cannot mitigate it, so this
point should be established. The second question is whether or not agriculture can really
mitigate greenhouse gas emissions. Chapter 2 reviews both these questions. In so doing, it
will show that the answers to both of these questions are based on a highly inductive type of
science, and, given that anthropogenic climate change is disputed, it is necessary to say
whether or not this is an adequate basis for action. This is discussed in chapter 3.

The fourth question is whether or not carbon is a commodity that can be priced, bought and
sold in any meaningful sense. Does it really have a market value? Our understanding of value
in a market society would suggest not. If this is the case, then the “carbon market” is a
bureaucratic fiction that farmers would do well to avoid. And even if one accepts that carbon
does have value, how would one price it? If that is not possible, then the answer to the fourth
question would have to be no. Much of chapter 4 is devoted to the fourth question. If the
answer to it is yes, a fifth question would still arise as to whether it should be bought from
developing countries; surely there are ethical questions around becoming wealthy as a society

14


by emitting carbon, and then buying off one’s obligations. This is a difficult question for
anyone who values equity in environmental management, and chapter 4 reviews this before
finishing with a discussion of the market as it has evolved so far.

The sixth question is whether agricultural sinks can be fitted into any carbon trading or
funding system. This involves many subsidiary questions. The first is whether a market exists
for this sort of carbon credit, given that agricultural sinks present difficult issues in terms of
transaction costs and comparative returns. On the face of it, modifying a power station
mitigates more CO2 emissions for a given investment. Chapter 5 reviews this question. It
goes on to look at some of the very practical constraints to agricultural sinks; how for

example to deal with baseline-setting, additionality, leakage, permanence and – an especially
complex area – monitoring and verification. Chapter 5 deals with problems that are specific
to agricultural sinks, but it will be seen that they reflect back on the world climate-change
regime, showing that it must accommodate itself to the scientific and managerial realities of
any industry with which it deals.

The seventh question is what might be learned from a case study in a given area, looking at
how sequestering carbon would fit around farmers’ own needs and concerns, and within the
macroeconomic context in which those farmers work. This was done with a case study in the
Atlantic Forest region of Brazil. Chapter 6 explains how carbon stocks have related to land
use within the context of the region’s history. It also sets out the methodology chosen for
assessing potential for a sinks project. Chapter 7 gives the result of this assessment.

Chapter 8 sets out the conclusions. The answers to most of these questions are complicated,
even messy – especially where technical and administrative constraints are concerned. But
2012 is not far away, and policy decisions will be needed quickly if agriculture is to be part
of any Kyoto II.

15


2

Climate change and agriculture
The movements of the air and the waters, the
extent of the seas, the elevation and the form of
the surface, the effects of human industry and
all the accidental changes to the terrestrial
surface modify the temperatures in each
climate. The characters of phenomena due to

general causes remain; but the thermometric
effects observed at the surface are different to
those which would take place without the
accessory causes.
Jean-Baptiste Fourier, Memoire sur
les temperatures du globe terrestre et
des espaces planetaires (1827), trans.
W. M. Connolley

T

he hypothesis tested in this thesis is that agriculture could, with improved management
practices, absorb a significant amount of CO2 as organic carbon and that farmers in the

developing world might benefit from its value as a mitigation strategy for climate change.
But this hypothesis presupposes that climate change is taking place and is due in part to CO2,
that agricultural soils could hold more of it than they do, and that it would have much impact
on climate change if they did. As these are large assumptions, this chapter reviews them.

2.1

Anthropogenic climate change

The notion that human activity changes the climate is not new. In the Middle Ages, it was
thought magic was the human agency, and that burning witches would alleviate flood or
drought. This persisted. Baliunas (2004) argues that the Little Ice Age of roughly 1500-1750,
following as it did a warmer mediaeval climate, provoked a wave of witchhunts and several
thousand executions appear to have taken place in Bamberg, Würzburg, Electorate Mainz and
Westphalia in 1626 as a response to a severe late frost that destroyed both grain and vine in
the spring of that year, prompting popular wrath at tolerance of witchcraft.

However, anthropogenic climate change was probably first considered in the modern sense in

16


the early 19th century when French scientist Jean-Baptiste Fourier put forward the view that
gases in the atmosphere affected the surface temperature of the earth through a “greenhouse
effect”. Fourier constructed his theory not long before his death in 1830, and did little to link
this effect to human activity. It would be left to Irish-born researcher John Tyndall, later in
the century, to identify the causative gases; he would also be the first to demonstrate the
“greenhouse” phenomenon in the laboratory, where he used the first ratio spectrophotometer
to establish the different absorptive powers between a number of gases, including CO2
(Fleming, 1998: 1). In the early 20th century Nobel laureate Svante Arrhenius calculated the
probable influence on the climate of a rise or fall in CO2 concentrations – the first attempt to
quantify it as such; a 2.5 times or threefold increase would, he thought, warm the Arctic
regions by 8-9 deg C (Earth Observatory, 2005a: 1). Although both Fourier and Tyndall
understood that some “greenhouse gases” were emitted by human activity, Arrhenius seems
to have been the first to argue that this could really change the climate. This left him
untroubled. It would, he suggested, produce more food; and, being Swedish, he might have
welcomed a warmer winter.
The perception that anthropogenic climate change might be a threat is relatively recent. In
1958 the Scripps Institution of Oceanography began to monitor atmospheric CO2 at the
Mauna Loa observatory in Hawaii (Earth Observatory, 2005b: 1); the previous year, Roger
Revelle and Hans Suess had demonstrated the anthropogenic effect on the atmospheric C
pool in a seminal article in Tellus (ibid; Scripps Institution, 2005: 1). In 1965 Revelle brought
the potential dangers to public and Government attention as a member of the President’s
Science Advisory Committee Panel on Environmental Pollution.
Today, thanks to techniques such as the analysis of ice cores, it is possible to measure historic
CO2 levels and thus tie the increase in atmospheric CO2 more or less to the Industrial
Revolution:

Before the Industrial Era, circa 1750, atmospheric carbon dioxide (CO2 )
concentration was 280 ± 10 ppm for several thousand years. It has risen
continuously since then, reaching 367 ppm in 1999. The present
atmospheric CO2 concentration has not been exceeded during the past
420,000 years, and likely not during the past 20 million years. The rate of
increase over the past century is unprecedented, at least during the past
20,000 years. (IPCC, 2001a: 185.)
However, it is one thing to identify and measure anthropogenic greenhouse emissions, but
another to quantify the results. Tyndall established the differential conductivity of the gases

17


present in 1859, but this does not in itself permit projection of climatic effects. For example,
atmospheric carbon is increasing at only half the rate of emission from fossil fuels, due to
terrestrial uptake (op. cit.: 187). But no-one is sure exactly where this remaining 50% is
going; it is being absorbed by forests, soils and oceans, but these processes cannot yet be
accurately quantified – giving rise to the notorious “missing sink”. Moreover there are
substantial year-on-year variations; the rate of increase was 3.3 ± 0.1 PgC/yr during 1980 to
1989 and 3.2 ± 0.1 PgC/yr during 1990 to 1999 (op. cit.: 185), but 1992’s figure was 1.9 PgC
and 1998 6 Pg C, thanks mainly to variation in terrestrial uptake itself induced by volcanic
activity and/or climatic variation. Not least of the factors here could be terrestrial feedbacks
to climate change from processes that it has itself provoked – for example, emissions from
sinks such as agricultural land and in particular, peat bogs, where higher temperatures could
induce faster mineralization of soil C. These factors must be built into any future projection
although they remain highly uncertain. Moreover these projections – the product of General
Circulation Models, or GCMs – do not always agree in their assessment of either past or
future climatic trends.
So GCMs, on which forecasts of climate change depend, could be presented as informed
speculation. Whether or not they are viewed as such may depend on one’s assessment of

induction as a tool of enquiry. This is discussed in Chapter 3. For the moment, it should be
noted that the uncertainty of GCMs has helped fuel the scepticism of commentators such as
Bjørn Lomborg (Lomborg, 2001), considered in 2.1.3 below. First it is worth looking at the
probable impacts of climate change; that they are worth mitigating is also an underlying
assumption of this thesis and should be examined.
2.1.2

What climate change will do

For much of the 20th century, the global surface temperature increased at about 0.15 deg. C
per decade. The fourth Assessment Report of the Inter-Governmental Panel on Climate
Change (IPCC) states that 11 of the 12 years 1995-2006 were amongst the 12 warmest years
since 1850, and that the 100-year linear trend to 2000 had been an annual increase in global
surface temperatures of 0.74 deg. C, a little higher than supposed at the time of the Third
Assessment Report, which put it at 0.6 deg. C (IPCC, 2007a: 5).
The IPCC has put together a series of projections of future trends. Finalized just too late for
the Third Assessment Report, they were summarized in it in provisional form and then
published shortly afterwards in the Special Report on Emissions Scenarios, or SRES (IPCC,
2001b), which is extensively quoted in the Summary for Policymakers of the Fourth

18


Assessment Report (IPCC, 2007a). The SRES seeks to project emissions scenarios according
to different economic and social trends, and in so doing it indicates how complex climate
forecasting would be even if GCMs were known to be precise. The report produced no less
than 40 scenarios, eventually amalgamated into just four basic “marker” scenarios labelled
A1, A2, B1 and B2. A1 assumes rapid economic growth, a population peak in mid-21st
century, and reductions in income disparities. Given this background, it subdivides into three
possible fossil-fuel use scenarios: intensive, use of alternatives, or a balance across several

sources. The other three groups also assume different combinations of economic growth,
shifts to service economies and balances of sustainable and other energy sources.
The resulting emissions projections cover a very broad range even when run through only one
or two GCMs, a source of variability in themselves. For a start, the Third Assessment Report
projects carbon emissions by 2100 at anything from 770 to 2,540 Pg C. The IPCC states that
variations in “climate sensitivity and ocean and terrestrial model responses” add at least -10%
to +30% uncertainty to the level of atmospheric C that this would create. Once uncertainties
as to terrestrial feedbacks have been incorporated, this would indicate atmospheric CO2
concentrations of anything between 490 and 1,260ppm, or between 75% and 350% above
those in 1750, at the dawn of the industrial age. Thus the global average temperature increase
was projected at anything between 1.4 and 5.8 deg. C above 1990 in the Third Assessment
Report. The Fourth Assessment Report is a little more pessimistic, suggesting a likely range
of 1.8 deg. C to 6.4 deg. C., which it suggests is more accurate as it is based on “a larger
number of climate models of increasing complexity and realism” (IPCC, 2007a: 13), and also
now incorporates some information on feedbacks in the climate cycle. This is important
because rising temperatures could (for example) increase the rate of mineralization of soil C,
which could in turn accelerate the rise in temperature. It should be noted that the upper range
is predicated on the A1F1 scenario, that is “a future of very rapid economic growth” which is
fossil-fuel intensive, albeit with more efficient technology. However, the lower, B1, scenario
posits a less globalized world and “intermediate” economic growth, with emphasis on local
solutions. Neither seems entirely likely; the A1 scenario is perhaps more probable, but on the
other hand all scenarios omit any type of international agreement to limit emissions (op. cit.:
18); so on balance we might expect something halfway between the upper and lower bound.
Predicting what such rises in temperature would mean in practice is yet more complex. In
general, precipitation is likely to rise in higher latitudes all the year round, with increases in
winter in tropical Africa and in summer in South-east Asia. In Australia, southern Africa and

19

central America, however, winter rainfall is expected to decrease. In fact, the Fourth
Assessment Report states that the 20th century also saw land-surface rainfall in the subtropics decrease by about 0.3% a decade. The picture is less clear for the tropics, where it has
increased by roughly the same amount, but not in the last few decades. However, there is
some evidence that it has increased over the oceans. Over the last century, there has been a
“significant” rise in precipitation over the eastern parts of North and South America, northern
Europe and northern and central Asia, but a decline over the Sahel, Mediterranean, southern
Africa and parts of southern Asia (op. cit.: 7).

Intensity of precipitation is seen as increasing almost everywhere, as is the frequency of
extreme precipitation events (IPCC, 2001b: 71-72). This would surely provoke more soil
erosion, especially in fragile, semi-arid environments where rainfall is already very
concentrated in time and space. More generally, food production is likely to suffer (IPCC,
2001c: 11). The rising level of malnutrition is also seen as causing impaired child
development and “decreased adult activity” (op. cit.: 12) – while the geographical reach of
malaria and dengue is expected to increase. On one projection, an additional 300 million
people could be at risk from falciparum (cerebral) malaria by 2080, and perhaps 150 million
from vivax malaria (Martens et al., 1999: S102). The IPCC also adds that: “Extensive
experience makes clear that any increase in flooding will increase the risk of drowning”
(IPCC, 2001c: 11).
An indication of the uncertainty involved is the effect on food production. Not least of the
variables is how the CO2 “fertilisation effect” will act on it and on terrestrial CO2 uptake.
However, the more general uncertainty is exemplified by the trends in African and Latin
American maize production projected by Jones and Thornton (2003). They foresee three
basic types of response to climate change. One, to be sure, is grim – maize yields collapse
and human populations are displaced as a result (op. cit.: 55). This appears to be mainly a
consequence of changing rainfall patterns. In other cases, however, the crop benefits; they see
the Ethiopian highlands around Addis Ababa as experiencing anything up to 100% yield
increases, while in other areas, such as eastern Brazil, there will be yield decreases but within
a scale that can be dealt with through crop breeding and improved agronomy. It is necessary
to accept that any of these outcomes are possible and must be allowed for.

This uncertainty is naturally reflected in the forecast of economic impacts. The IPCC’s
Second Assessment Report suggested that a doubling of CO2 would cost about 1.5% of GNP,

20


but this is now thought to have been pessimistic (Mendelsohn and Williams, 2004: 316).
However, costing environmental change on a global basis is not always helpful. There is a
similarity here with land degradation; as Scherr (2001: 155-170) has explained, it could cut
production by up to 17% by 2030, but the world food system would adjust for these losses.
However, the impacts would be felt severely at a local level, where they would be worst for
the poorest (ibid.). Climate change is no different in this respect. Thus one scenario has large
losses in the tropics counterbalanced by big productivity gains in, particularly, the former
Soviet Union and Eastern Europe. But another scenario suggests that “the damages in the
tropics and especially Asia are so large that the high latitude gains pale in comparison”
(Mendelsohn and Williams, 2004: 323-324). Parry et al. (1999: S51) suggest that there could
be between 55 and 65 million extra people at risk of hunger in Africa by 2080 because of
climate change.
There is much that is not yet clear in all of this, not least because of potentially complex, nonlinear response. For example, the main factor in climate change that affects crop production is
rainfall, but much may also turn on whether faster mineralization of organic matter under
higher temperatures would cancel out the CO2 fertilisation effect, a question discussed later in
this chapter. And there will be plenty of other variables; apparently similar agro-ecological
zones would have significant differences in vulnerability depending on the ability of their
soils to retain moisture, the propensity of the local farmers to maintain cover crops, and their
access to crop varieties bred for moisture stress (or simply to adaptable landraces and wild
relatives). These complexities underpin a growing research effort on vulnerability and
adaptation to climate change and the factors that influence them.
So there is enormous uncertainty around future emissions scenarios, the changes they would
effect on the atmospheric CO2 pool, the consequences of such changes and the extent to
which people might be better off adapting to them, rather than trying to prevent them. This

uncertainty has been used by the United States to negate commitment to emissions reductions
– what might be called the “uncertainty scepticism”. Moreover it is not impossible that
climate change might be beneficial in some ways – a view taken, as mentioned above, by
Arrhenius himself. This might be called “optimist scepticism”. If either view is correct, there
is no justification for interfering with farming systems in developing countries – the dangers
of which are all too clear from some past attempts to deal with soil erosion, as described in
chapter 6.
In fact, I am satisfied that anthropogenic climate change is a threat and that its mitigation is

21


justified. However, it seems improper to make so large and bald a statement without
examining the sceptical view at least briefly. The “uncertainty” thesis will therefore be
examined with reference to one of its chief proponents, Bjørn Lomborg. The “optimist”
discussed will be Sylvan Wittwer, who has argued that CO2 fertilisation will result in the
production of more food (an argument also advanced by Lomborg). They are not the only
ones to question the current consensus on climate change, but their work has direct relevance
to two of the main strands of the “sceptic” argument, so they are good proxies for the others.
2.1.3

The sceptics

Lomborg’s 2001 book The Sceptical Environmentalist sought to refute what he called the
“Litany” – the constant stream of dire warnings from environmentalists about everything
from water to GMOs to climate that, he argued, should not be allowed to undermine progress
towards a better world, especially for the poor (Lomborg, 2001: 351). Lomborg accepts
anthropogenic climate change; indeed he acknowledges a cost of US$5 trillion. His argument
is that it is not cost-effective to try to prevent it, and that more lives will be saved by spending
on water and sanitation, and on adaptation to climate change. This view is based in part on

the uncertainty of global change predictions, which he sees as exaggerated. There are some
problems with his arguments, as will be shown. However, the basic thesis – that since no-one
knows quite what is coming, the optimal response to climate change is to accept it and deal
with it – is not inherently unsound, and he nowhere denies the fact of anthropogenic climate
change or suggests that its victims do not matter.
Despite this, Lomborg has been the target of immoderate and discourteous criticism. IPCC
chairman Rajendra Pachauri asked what the difference was between Lomborg’s view of
humanity and Hitler’s (Global Warming Updates, 2004). Even Nature published a review of
The Sceptical Environmentalist (Pimm and Harvey, 2001) in which Lomborg’s reasoning is
compared, by implication, to that of a homophobic Holocaust denier. In January 2002
Scientific American went so far as to publish an 11-page rebuttal of the book; this included a
section on climate change (Schneider, 2002). This answered relatively few of the questions
Lomborg had raised. Schneider does reasonably criticize Lomborg’s rather arbitrary cost
estimates, yet does not really acknowledge the massive uncertainty that surrounds any costing
of climate change.
However, Lomborg’s arguments tend to work better in theory than practice. A typical
example is that any rise in sea levels will hurt no-one because it will be economically
worthwhile for governments to protect their citizens, and it therefore “seems likely that rich

22


countries (as almost all countries will be at the end of this century) will protect their citizens
at such a low price that virtually no one will be exposed to annual sea flooding” (Lomborg,
2001: 290). This is the voice of a man with a belief in perfect markets. Low-income countries
will not find the resources for flood protection on the scale needed where populations are
heavily dependent on low-lying coastal land.
Even where the resources exist and the rationale is indisputable, there may be inaction. In
2002 the US Army Corps of Engineers undertook an initial reconnaissance regarding the
strenPghening of New Orleans’s flood defences to deal with Category 4 and 5 hurricanes.

The cost of a five-year feasibility study was estimated at US$8 million, with the project itself
expected to take 10-20 years and cost US$2.5 billion. The feasibility study was not included
in the President’s request for fiscal year 2006 (Carter, 2005: 6). Indeed funding for civil
works on Lake Ponchartrain had been declining since 1996 (op. cit.: 5). By mid-September
2005, the Swiss reinsurance specialist Swiss Re envisaged insurance payouts of around
US$40 billion, with an American industry specialist putting insured losses at US$60 billion
and uninsured at US$125 billion1 (BBC, 2005: 1). This was a very bad bargain and it was at
least partly foreseen. So it is wrong to assume that governments will help their people adapt
even when they have the means. The assumption that all countries will be rich by 2100 is also
a large one. This is no argument against mitigation.
However, Lomborg is not a specialist in any of the fields he discusses, and it is worth
examining a “sceptic” who bases his scepticism on his own discipline. Sylvan Wittwer is a
horticulturalist and former head of the Agricultural Experiment Station at Michigan State
University. He has argued that the CO2 fertilization effect will mitigate any effect climate
change has on food supplies. Elevated levels of CO2 cause partial closing of plant leaf
stomata, reducing transpiration for a given area and raising leaf temperature (Wittwer, 1995:
2). More of the CO2 taken in by the plant is converted to plant material. This is important for
two reasons. First, it implies that, far from damaging agriculture by changing the climate,
increasing CO2 levels may make it more profitable – not least because reducing transpiration
also improves water-use efficiency, potentially vital in the arid areas that will be most
vulnerable to climate change. Second, it may change the balance between photosynthesis and
autotrophic respiration – that is to say, plants may convert a greater percentage of their CO2
1

These figures for damages cover Katrina as a whole, not just New Orleans, and some of those lying
outside area that would have been covered by the proposed scheme would have been substantial (for
example, the Gulf oil platforms). However, it seems certain that much of the loss was incurred in New
Orleans – and certainly more than US$2.5 billion.

23

intake into organic matter, instead of re-releasing it. 2 This increase in net primary
productivity (NPP) would thus be mitigating climate change through reduction of the
atmospheric CO2 pool. In his 1995 book Food, Climate and Carbon Dioxide, Wittwer states
that the “positive, beneficial and directly measurable” effects of increased atmospheric CO2
are “glossed over lightly or submerged in a series of catastrophic issues. These are associated
with a widely promulgated global warming, which has been greatly exaggerated… and which
may not even exist” (Wittwer, 1995: 2).
This book is now 12 years old, but Wittwer continues to advise the Center for the Study of
Carbon Dioxide and Global Change, which publishes an on-line bulletin, CO2 Science. 3 The
central aim seems to be to argue that rising levels of CO2 will be beneficial to humanity. 4
That increased levels of CO2 will increase productivity in some cases is not in doubt, so it is
worth considering this argument.
The IPCC also acknowledges that the resulting increase in NPP will have climate feedback
effects (IPCC, 2001a: 51). However, the extent to which NPP increases, the probability of
increased food production, and whether there is a negative feedback on climate change, are
dependent on several variables. Improvements in water-use efficiency (WUE) will not be
significant in non-water-stressed environments, where it is not an issue (Dubrovsky et al.,
2000: 2). It may also be unhelpful in environments that are very water-stressed, as it is
pointless using water better if there isn’t any.
Moisture apart, increased temperature would also offset gains to some extent, especially in
heat-stressed environments. Planting dates can (and probably often will) be altered to allow
for rising temperatures, but this will be constrained by photoperiod and perhaps by less
predictable rainfall. Indeed Canadell et al. (2007: 372) suggest that the gains will be offset by
heterotrophic respiration. Last but not least, species with different photosynthetic pathways
will react differently; plants with a C3 pathway usually respond to elevated CO2, but those
with a C4 pathway are already more efficient in their processing of CO2, and show less or no
2
Although a distinction should be made between autotrophic respiration, in which the CO 2 returns to

the atmosphere from the plant tissues itself, and heterotrophic respiration, which could involve the
decomposition of organic matter which has already ceased to be part of a living plant. In the former
case, the extent of respiration is directly significant to farm productivity; in the second it is indirectly
important for productivity, especially in the long term, and would be just as important in terms of
climate feedback. As the IPCC points out (IPCC, 2001a: 190), the carbon all goes back into the
atmosphere eventually.
3
www.co2science.org.
4
Along, perhaps, with a general scepticism; the site includes a feature called “Medieval Warm Period
of the Week”.

24


response (IPCC, 2001a: 195). The first type includes most plants in colder climates, wheat,
rice and most agricultural crops. However, the second includes maize and sugar cane; also
tropical and some temperate grasses. This could imply positive feedback effects to climate
change, as loss of C through decomposition of organic matter is likely be much faster in
tropical climates where C4-type plants are more likely to predominate. So organic matter will
not accumulate any more quickly but may break down faster as the temperature rises. As
organic matter content is important for productivity, this will in some cases reduce NPP,
further reducing the accumulation of soil organic matter.
Moreover, “real-world” response of even C3 plants to elevated CO2 is imperfectly
understood. The standard technique for measuring response has been to use chamber
fumigation, but as Morgan et al. (2005: 1857) report, using free-air CO2 enrichment (FACE)
simulates elevated CO2 levels without otherwise altering the microclimate; they also permit a
trials area large enough for the destructive harvests needed in order to monitor the crop
throughout its growth. The authors report previous FACE trials that suggest wheat and rice
response to elevated CO2 levels rather lower than that predicted by chamber studies (ibid.);

moreover their own FACE trials with soybean, also a C3 plant, showed a substantially lower
increase in yield than would have been expected on the basis of previous chamber studies.
They argue that future projections of global food supply increases may be optimistic (op. cit.:
1864).
Parry et al. (1999: S56) list further uncertainties in predicting yield response (and presumably
NPP too) from trials: weeds, diseases and insect pests are assumed to be controlled; there are
no soil problems (for example acidity or salinity); and no extreme weather events. Parry et al.
(2004: 66) also modelled the yield of the world’s major food crops against the IPCC’s SRES
scenarios, and suggested yield declines of 0%-5%. However, they warn that these results are
in part dependent on the CO2 fertilization effect being fully realized, and stress the
uncertainties around this. But they suggest that, should the CO2 fertilization effect be
“drowned out” by changes in climate, yield decreases of 9%-22% are possible under the
SRES scenarios (ibid.).
Alternatively, if it does make itself felt, it may do so in a negative way. For example, in 2007
CO2 Science reported the results of Bhatt et al. (2007), who had found that the dry-matter
yield of the grass species Cenchrus ciliaris increased by 193% with a CO2 enrichment of
240ppm. “Surely, such a response will be an enormous boon to the many people living in the
arid and semi-arid tropics in the years and decades to come, as the air’s CO2 content

25