Climate Change and World Agriculture

Martin L. Parry

• Publisher: Taylor & Francis
• Year: 2019
• eBook ISBN: 9781000692778
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Business General
• Index: Biological Sciences

Originally published in 1990, this book analysed the sensitivity of the world food system and looked at the variety of ways in which it would be affected by climate change. It describes the effects of climate change on agriculture, estimates the impacts on plant and animal growth and looks at the geographical limits to different types of farming. It also considers the range of possible ways to adapt agriculture and so to mitigate the disastrous consequences of climate change.

1. The Sensitivity of Agriculture to Climate

Introduction

In 1990 the Intergovernmental Panel on Climate Change (IPCC) completed its report on the greenhouse effect. The IPCC had been set up under the auspices of the World Meteorological Organisation and the United Nations Environment Programme, to examine how climate and sea level might change, what might be the impact of these changes and what could be the most appropriate response to them. IPCC Working Groups tackled each of these three tasks. Working Group II (Impacts) concluded that greenhouse gas-induced changes of climate would have an important effect on agriculture, with the most severe negative impacts probably occurring in regions of high present-day vulnerability that are least able to adjust technologically to such effects.¹ The purpose of this book is to consider, in more detail than could be covered within the confines of the IPCC report on agriculture, the reasoning behind this conclusion, its implications for global food security and the most appropriate courses of action.

Global Warming

The best judgement of the IPCC is that, if emissions of greenhouse gases (GHG) continue to grow as currently projected (a so-called “Business-As-Usual” scenario), then global mean temperatures will increase by 0.2°C-0.4°C per decade over the next century.² There is a quite clear indication that a warming of the globe has occurred over the past century, amounting to 0.3°C-0.6°C. Much of this warming has been concentrated in two periods, between about 1920 and 1940 and since 1975; the six warmest years on record have all been in the 1980s. The size of this warming is broadly consistent with the predictions of climate models but, because of the natural variability of the Earth’s climate, IPCC scientists are not yet able to say that they have detected the unequivocal “signal” of man-made climate change.²

The substantial uncertainties surrounding this issue are considered in the next chapter. For the present, let us consider in outline how the climate could change and, if it did, what would be the most likely consequences for world food supply.

Warming in high latitudes

There is relatively strong agreement that greenhouse gas-induced warming will be greater at higher latitudes.³ This would reduce current temperature constraints on agriculture and probably increase productive potential, particularly in northern parts of North America, Europe and Asia. Soil and terrain constraints are, however, likely to limit the actual increase in agricultural output here, and it is probable that such gains in potential at high latitudes will do little to compensate for quite possibly substantial losses in potential in mid- and low latitudes.⁴

Poleward advance of monsoon rainfall

In a warmer world monsoon rains would be likely to penetrate further poleward, both in Africa and Asia, as result of an enhanced ocean–continent pressure gradient (itself the result of more rapid warming of the land than the ocean in the pre-monsoon season).⁵ If this were to occur – and it should be emphasized that there remains much uncertainty here – then total rainfall could increase in currently drought-prone regions such as the Sahel and north-west India. It is possible, however, that the increase in rainfall would come largely in the form of more intensive rainstorms occurring over a shorter rainy period. If current levels of pre-monsoon rains, which are important for the germination of crops at the beginning of the growing season, were to diminish then growing seasons could be shortened and thus the potential for agriculture reduced. In addition, more intense rainfall could exacerbate problems of flooding and soil erosion.

Reduced crop-water availability

Probably the most important consequences of projected changes in climate for agriculture would stem from higher actual évapotranspiration, primarily as a result of higher temperatures of the air and land surface. Even in the tropics, where temperature increases are expected to be smaller than elsewhere, the increased rate of moisture loss from plants and soil would be considerable. It may be somewhat reduced by greater humidity and increased cloudiness during rainy seasons, but could be more pronounced in dry seasons.

Further details of these projected changes of climate, including the substantial uncertainties surrounding them, will be given in Chapter 2, and their implications for agriculture will be considered in subsequent chapters of this book. In one respect, however, the degree of vulnerability of agriculture to possible changes of climate is as much determined by the present-day vulnerability to weather as by the future patterns of climate change. This is considered in the next section.

The Most Vulnerable Regions

In many regions of the world agricultural production is currently limited by climate, most of this limitation being in developing countries. Insufficient rainfall is the main climatic limit in these areas, curtailing the growing period available for crops. Overall, 63 per cent of the land area of developing countries is climatically suited to rainfed agriculture, but this endowment varies considerably between regions;⁶ it amounts to as much as 85 per cent in South America and 84 per cent in south-east Asia, but is limited to 64 per cent in Central America and 53 per cent in Africa. The severest climatic limitations to agriculture are to be found in south-west Asia where 17 per cent is too mountainous and cool, and 65 per cent too dry, leaving only 18 per cent as potentially productive.⁶

The potential base for rainfed agriculture is therefore very limited in some regions and any further curtailment of potential due to changes of climate could severely strain their ability to feed local populations. Regions where climatic and soil resources are considered by FAO to be unable to meet the current needs of local populations are indicated in Figure 1.1. They occupy as much as 22 per cent of the global land area and contain 11 per cent of the world’s population. They are mainly located in the cool and cold tropics (e.g. the Andean region, the Maghreb in North Africa, the mountain regions of south-west Asia), the Sahel and the Horn of Africa, the Indian subcontinent, and parts of mainland and insular south-east Asia. We shall show later that some of these regions could...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Original Title Page
• Original Copyright Page
• Dedication Page
• Table of Contents
• Figures and Tables
• Abbreviations and Acronyms
• Preface
• 1. The sensitivity of agriculture to climate
• 2. Possible changes of climate
• 3. Methods of assessing impacts of climatic change
• 4. Effects on plants, soil, pests and diseases
• 5. Effects on agricultural potential
• 6. Effects on production and land use
• 7. Implications for global food security
• 8. Adapting to climatic change
• 9. Conclusions
• Further reading
• Notes and References
• Index