Lectures 3 -6: Climate and AgricultureLectures 3 -6: Climate and Agriculture

Prof Shellemiah O keyaProf Shellemiah O keya

66thth June 2013 June 2013

The Earth’s Environmental Woes:Is Agriculture Part of the Problem or Part of the Solution?

Reported by Ellen Wilson

Chapter 24: Global Warming changes the focus for Agriculture

Gommes, R. 1993. Current climate and population constraints on world agriculture. In: Agricultural Dimensions of Global Climate Change. H.M. Kaiser and T.E. Drennen (eds.). pp. 67-86.

Holmes, R. 1995. Arctic ice shows speed of climate 'flips'. New Scientist 145 (1967): 13.

Houghton, J.T., Meira Filho, L.G., Bruce, J., Lee, H., Callander, B.A., Haites, E., Harris, N. and Maskell, K. (eds.). 1995. Climate Change 1994. Radiative forcing of climate change; and an evaluation of the IPCC IS92 emission scenarios. Cambridge University Press, Cambridge, New York, Melbourne.

Kaiser, H.M. and Drennen T.E. (eds.). 1993. Agricultural Dimensions of Global Climate Change. St. Lucie Press, Delray Beach, Florida. 311 p.

Katz, R.W. and Brown, B.G. 1992. Extreme events in a changing climate: variability is more important than averages. Clim. Change 21: 289-302.

Keeling, C.D., Whorf, T.P, Wahlen, M. and van der Plicht, J. 1995. Interannual extremes in the rate of rise of atmospheric carbon dioxide since 1980. Nature 375: 666-670.

Kukla, G. and Karl, T.R. 1993. Nighttime warming and the greenhouse effect. Envir. Sci. Technol. 27 (8): 1468-1474.

Comprehend the close relationship Comprehend the close relationship between climate and agriculturebetween climate and agriculture

Establish that climate change affects Establish that climate change affects agriculture and vice versaagriculture and vice versa

Understand that adaptation to climate Understand that adaptation to climate change is central in agriculturechange is central in agriculture

Soils and Great/ Early CivilizationsGreat civilizations had good soils as one of their

natural resourcesIn Kenya the highest population density are in the

counties with good/fertile soils

Other examples of fertile soilsThe ancient dynasties of the Nile were made

possible by food producing capacity of the fertile soils of the valley and associated irrigation system. Tigris and Euphrates rivers in Mesopotamia and Indus, Yangtse and Huang Ho rivers in India and China respectively represent inhabitants of flourishing civilization

These fertile soils made possible stable and organized communities and even cities

In contrast to nomadic, shifting societies associated upland soils with concomitant animal grazing

Soils destruction or degradation or mismanagement was also associated with the downfall of some of these civilization that good soils had helped to build

In the Euphrates and Tigris the elaborate irrigation and drainage systems were not maintained – resulting in accumulation of salts;

And once the productive soils became barren and useless;

The flourishing cities that had occupied these areas fell into ruins and the people migrated elsewhere;

The ruins of Babylon in Syria is a living example;

Thus people are dependent on soils and to an extent good soils are dependent on people.

Most people settle where the best soils are...

Soil formation is intrinsically linked to Soil formation is intrinsically linked to climateclimate

Soil formation is a function of:Soil formation is a function of:

Climate + Vegetation+ Parent material Climate + Vegetation+ Parent material +Topography + Time+Topography + Time

Climate has a dominant factor in the soils that Climate has a dominant factor in the soils that you seeyou see

Agriculture systems : Agriculture systems : Climate systemClimate systemCrop agriculture, Crop agriculture, Cloudiness, wind, rain , Cloudiness, wind, rain ,

evaporation evaporation Animal husbandry, Animal husbandry, TemperatureTemperatureForestry and Forestry and Fisheries can be defined as one of the systems, and Fisheries can be defined as one of the systems, and

climate the other. climate the other. If these systems are treated independently, this would If these systems are treated independently, this would

lead to an approach which is too fragmentarylead to an approach which is too fragmentary

Tropical rainforest – found particularly in the Tropical rainforest – found particularly in the centre of the continent, and along the eastern coast centre of the continent, and along the eastern coast of Madagascar.of Madagascar.

Humid sub-tropical – found in the south-west.Humid sub-tropical – found in the south-west.Mediterranean –  mostly on the north-west Mediterranean –  mostly on the north-west

(Mediterranean) coast and in the south-east(Mediterranean) coast and in the south-eastSavannah – found to the north and south where it Savannah – found to the north and south where it

replaces the rain forest. There are distinct wet and replaces the rain forest. There are distinct wet and dry seasons.dry seasons.

Land degradation

Biodiversity loss

Vicious circle

Climate change

•Precipitation

•Evapo-transpiration

= Aridity Index ~ potential productivity

Humid

Aridity Index AI < 0.05

0.05 < AI < 0.20

0.20 < AI < 0.50

0.50 < AI < 0.65

AI > 0.65 Humid

Semiarid

Dry subhumidSemiarid

Semiarid

Humid

Dry subhumid

1931-1960 1961-2000

Climate change-induced change in Aridity Index (P/PET) - productivity reduction

1931-1960 1961-1990

25 Mha Humid Dry sub-humid

Hyper arid 51 Mha Arid

3 Mha Semi arid Arid

Hulme, M. et al., Climate Research, 1992

Sciortino, M. et al. 2010 (submitted)

Sicily

Africa

Droughtsfires, floodsIncreased• frequency• intensity

Land degradationVicious circle

Reduced biological productivity of economic value

Reduced carbon fixation and sequestration

Global carbon stocksReduced SOC depletion

Loss of -•nutrients •soil moisture

Diversity of soil vegetation cover

Reduced

Soil protectionDegraded

SOC in eroded soil oxidizes Increased emissions

Biodiversity loss•Precipitation

•Evapo-transpiration

•Soil moisutre

change

increasedecrease

Climate change& agrodiversity failure

•Crop failure•Forage decline

& increased CO2

Species differential • sensitivity to climate change• response to elevated CO2

Soil erosion

Steppe – away from the Equator, to the north Steppe – away from the Equator, to the north and south, the savannah grades into drier and south, the savannah grades into drier steppe.steppe.

Desert – little rainfall, and big daily differences Desert – little rainfall, and big daily differences between day and night temperatures.between day and night temperatures.

The Sahara in the north is the world’s biggest The Sahara in the north is the world’s biggest desert. desert.

Only three countries cover a greater area – Only three countries cover a greater area – Russia, Canada and China. Russia, Canada and China.

The Kalahari in Southern Africa covers an area The Kalahari in Southern Africa covers an area larger than France.larger than France.

Highland – largely found in the east, below the Highland – largely found in the east, below the Horn of Africa.Horn of Africa.

Marine – largely in the south-east.Marine – largely in the south-east.

Becoming more global. Becoming more global. It is now widely held view that human It is now widely held view that human

activities can affect climate, one of the activities can affect climate, one of the components of the environment. components of the environment.

Climate in turn affects agriculture, the Climate in turn affects agriculture, the source of all food consumed by human beings source of all food consumed by human beings and domestic animals. and domestic animals.

Climate may be changing, Climate may be changing, Human societies and agriculture Human societies and agriculture

development trends constraints climatedevelopment trends constraints climate

THE CLIMATE 'COMPLEX THE CLIMATE 'COMPLEX Climate variability is likely to increase under global Climate variability is likely to increase under global

warming (Katz and Brown, 1992), warming (Katz and Brown, 1992), The rate of change itself is extremely importantThe rate of change itself is extremely importantChanges would be associated with dramatic effects Changes would be associated with dramatic effects Ocean waters and associated products Ocean waters and associated products Cause havoc to established national fishery activitiesCause havoc to established national fishery activitiesWould make adaptation to climate change difficultWould make adaptation to climate change difficult

Most agricultural planning would be Most agricultural planning would be extremely difficult. extremely difficult.

 

Important greenhouse gases are:Important greenhouse gases are:Carbon dioxide (COCarbon dioxide (CO22),),

Methane (CHMethane (CH44), ),

Nitrous oxide (NNitrous oxide (N22O),O),

Troposphere ozone (OTroposphere ozone (O33) and ) and

Chlorofluorocarbons (CFCs). Chlorofluorocarbons (CFCs).

Basic characteristics of the first three gases are given later Basic characteristics of the first three gases are given later

The degree to which these greenhouse gases stem from The degree to which these greenhouse gases stem from agricultural sources is also important agricultural sources is also important

DeforestationDeforestationWetland riceWetland riceRuminantsRuminantsBiomass burningBiomass burningSynthetic fertilizersSynthetic fertilizersManures and animal excretaManures and animal excreta

The following are significant trends for the The following are significant trends for the near future:near future:

World production of cereals will continue to grow, World production of cereals will continue to grow, Export of cereals will undergo a modest growth in demand; Export of cereals will undergo a modest growth in demand; The livestock sector in developing countries will continue to The livestock sector in developing countries will continue to

grow;grow;Root crops, tubers and plantains will retain their Root crops, tubers and plantains will retain their

importance; importance; Oil crops will undergo rapid growth in developing countries; Oil crops will undergo rapid growth in developing countries; most importantly, most importantly, Many developing countries will become net agricultural Many developing countries will become net agricultural

importers.importers. 

Overall predictability of weather and climate would Overall predictability of weather and climate would decrease, making the day-to-day and medium-term decrease, making the day-to-day and medium-term planning of farm operations more difficult; planning of farm operations more difficult;

Loss of biodiversity from some of the most fragile Loss of biodiversity from some of the most fragile environments, such as tropical forests and environments, such as tropical forests and mangroves; mangroves;

Sea-level rise (40 cm in the coming 100 years) would Sea-level rise (40 cm in the coming 100 years) would submerge some valuable coastal agricultural land; submerge some valuable coastal agricultural land;

Incidence of diseases and pests, especially alien ones, Incidence of diseases and pests, especially alien ones, could increasecould increase

Present (agro) ecological zones could shift in some cases over Present (agro) ecological zones could shift in some cases over hundreds of kilometers horizontally, and hundreds of meters hundreds of kilometers horizontally, and hundreds of meters attitudinally,attitudinally,

With the hazard that some plants, especially trees, and With the hazard that some plants, especially trees, and animal species cannot follow in time, and that farming animal species cannot follow in time, and that farming systems cannot adjust themselves in time; systems cannot adjust themselves in time;

Higher temperatures would allow seasonally longer plant Higher temperatures would allow seasonally longer plant growth and crop growing in cool and mountainous areas, growth and crop growing in cool and mountainous areas, allowing in some cases increased cropping and production.allowing in some cases increased cropping and production.

In contrast, in already warm areas climate change can cause In contrast, in already warm areas climate change can cause reduced productivity; reduced productivity;

The current imbalance of food production between cool and The current imbalance of food production between cool and temperate regions and tropical and subtropical regions could temperate regions and tropical and subtropical regions could worsen.worsen.

The greenhouse gases CHThe greenhouse gases CH44, N, N22O and O and

chlorofluorocarbons (CFCs) have no known direct chlorofluorocarbons (CFCs) have no known direct effects on plant physiological processes. effects on plant physiological processes.

They only change global temperature and are They only change global temperature and are therefore not discussed further. therefore not discussed further.

Instead, concentration should be on the Instead, concentration should be on the effects of effects of increased COincreased CO22 tropospheric O tropospheric O33, increased UV-B , increased UV-B

through depleted stratospheric ozone,through depleted stratospheric ozone,Increased temperatures and the associated Increased temperatures and the associated

intensification of the hydrological cycle. intensification of the hydrological cycle. CARBON DIOXIDE CARBON DIOXIDE

COCO22 is an essential plant 'nutrient', is an essential plant 'nutrient', In addition to light, In addition to light, Suitable temperature, water and chemical elements such Suitable temperature, water and chemical elements such

as N, P and K, and it is currently in short supply. as N, P and K, and it is currently in short supply. Higher concentrations of atmospheric COHigher concentrations of atmospheric CO22 due to due to

increased use of fossil fuels, deforestation and biomass increased use of fossil fuels, deforestation and biomass burning, can have a positive influence on photosynthesis burning, can have a positive influence on photosynthesis (Figure 1.2)(Figure 1.2)

Under optimal growing conditions of light, temperature, Under optimal growing conditions of light, temperature, nutrient and moisture supply, biomass production can nutrient and moisture supply, biomass production can increase, especially of plants with C3 photo-synthetic increase, especially of plants with C3 photo-synthetic metabolismmetabolism

With increased atmospheric COWith increased atmospheric CO22 the the

consumptive use of water becomes more consumptive use of water becomes more efficient because of reduced transpirationefficient because of reduced transpiration

This is induced by a contraction of plant This is induced by a contraction of plant stomata and/or a decrease in the number of stomata and/or a decrease in the number of stomata per unit leaf area. stomata per unit leaf area.

This restricts the escape of water vapour This restricts the escape of water vapour from the leaf more than it restricts from the leaf more than it restricts photosynthesis photosynthesis

(improved water-use efficiency WUE) (improved water-use efficiency WUE)

With the same amount of available water, With the same amount of available water, there could be more leaf area and biomass there could be more leaf area and biomass production by crops and natural vegetation. production by crops and natural vegetation. Plants could survive in areas hitherto too Plants could survive in areas hitherto too dry for their growth. dry for their growth.

Increased ultraviolet radiation (UV-B, between 280 and 320 Increased ultraviolet radiation (UV-B, between 280 and 320 nanometers), due to depletion of the stratospheric ozone layer, nanometers), due to depletion of the stratospheric ozone layer,

Mainly in the Antarctic region, may negatively affect Mainly in the Antarctic region, may negatively affect terrestrial and aquatic photosynthesis and animal health. terrestrial and aquatic photosynthesis and animal health.

Over the last decade, a decrease of stratospheric ozone was Over the last decade, a decrease of stratospheric ozone was observed at all latitudes (about 10% in winter, 0% during observed at all latitudes (about 10% in winter, 0% during summer and intermediate values during spring and autumn).summer and intermediate values during spring and autumn).

However, the 'Biological Action Factor' of UV-B can vary However, the 'Biological Action Factor' of UV-B can vary over several orders of magnitude with even slight changes in over several orders of magnitude with even slight changes in the amount and wavelength of UV-B. the amount and wavelength of UV-B.

There are damaging effects of increasing UV-B There are damaging effects of increasing UV-B on crops, animals and plankton growth. It has on crops, animals and plankton growth. It has been reported that UV-B affects the ability of been reported that UV-B affects the ability of plankton organisms to control their vertical plankton organisms to control their vertical movements and to adjust to light levels; movements and to adjust to light levels;

Reductions in yield of up to 10% have been Reductions in yield of up to 10% have been measured at experimentally very high UV-B measured at experimentally very high UV-B values, and would be particularly effective in values, and would be particularly effective in plants where the COplants where the CO22 fertilization effect is fertilization effect is strongest.strongest.

On the other hand, UV-B increase could On the other hand, UV-B increase could increase the amount of plant internal increase the amount of plant internal compounds that act against pests.compounds that act against pests.

 

Tropospheric ozone originates about half from Tropospheric ozone originates about half from photochemical reactions involving nitrogen oxides photochemical reactions involving nitrogen oxides (NO(NOxx), methane or carbon monoxide, and half by ), methane or carbon monoxide, and half by downward movement of stratospheric ozone. downward movement of stratospheric ozone.

High ozone concentrations have toxic effects on High ozone concentrations have toxic effects on both plant and animal life (German Bundestag, both plant and animal life (German Bundestag, 1991; 1991;

It is likely that ozone, in conjunction with other It is likely that ozone, in conjunction with other photo-oxidants, is contributing towards the 'new photo-oxidants, is contributing towards the 'new type of forest damage' observed in Europe and the type of forest damage' observed in Europe and the United StatesUnited States

In the tropics, tropospheric ozone concentrations In the tropics, tropospheric ozone concentrations are generally lower than at northern mid-latitudes.are generally lower than at northern mid-latitudes.

However, this does not apply to periods when However, this does not apply to periods when biomass burning releases precursor substances for biomass burning releases precursor substances for the photochemical formation of ozone. the photochemical formation of ozone.

Rising temperatures - now estimated to Rising temperatures - now estimated to be 0.2°C per decade, or 1 °C by 2040 be 0.2°C per decade, or 1 °C by 2040

Would diminish the yields of some Would diminish the yields of some crops, especially if night temperatures crops, especially if night temperatures are increased the temperature increase are increased the temperature increase since the mid-1940s is mainly due to since the mid-1940s is mainly due to increasing night-time temperatures,increasing night-time temperatures,

While COWhile CO22-induced warming would -induced warming would result in an almost equally large rise in result in an almost equally large rise in minimum and maximum temperaturesminimum and maximum temperatures

Higher temperatures could have a Higher temperatures could have a positive effect on growth of plants positive effect on growth of plants of the CAM type. They would also of the CAM type. They would also strengthen the COstrengthen the CO22 fertilization fertilization effect and the COeffect and the CO22 anti-transpirant anti-transpirant effect of Ceffect of C33 and C and C44 plants plants

Higher night temperature may Higher night temperature may increase dark respiration of plants, increase dark respiration of plants, diminishing net biomass diminishing net biomass production; production;

Higher night temperature may increase Higher night temperature may increase dark respiration of plants, diminishing net dark respiration of plants, diminishing net biomass production; biomass production;

Higher cold-season temperatures may Higher cold-season temperatures may lead to earlier ripening of annual crops, lead to earlier ripening of annual crops, diminishing yield per crop, but would diminishing yield per crop, but would allow locally for the growth of more crops allow locally for the growth of more crops per year due to lengthening of the per year due to lengthening of the growing season. Winter kill of pests is growing season. Winter kill of pests is likely to be reduced at high latitudes, likely to be reduced at high latitudes, resulting in greater crop losses and higher resulting in greater crop losses and higher need for pest control; need for pest control;

Higher temperatures will allow for more Higher temperatures will allow for more plant growth at high latitudes and plant growth at high latitudes and altitudes.altitudes.

Restoration

What can be done in drylands?and likely to apply to non-drylands too

Soil depleted Soil salinized Range degraded

After 35 y - twice as much SOM After 35 y - twice as much SOM as the adjacent non-forested, as the adjacent non-forested, degraded landdegraded land

Arid dryland

Increasing C stocks

Reducing C emissions

Reducing poverty

Food security

AfforestationRunoff harvesting•Builds soil•Halts erosion•Regulates water•Promotes forage•Provides firewood

Transfer to patch cultivation -agroforestry

Below-ground SOMAbove-ground stand

Soil salinized Range degraded

The extra precipitation on land, if The extra precipitation on land, if indeed including present sub humid indeed including present sub humid to semi-arid areas, will increase to semi-arid areas, will increase plant growth in these areas, leading plant growth in these areas, leading to an improved protection of the to an improved protection of the land surface and increased rain fed land surface and increased rain fed agricultural production; in already agricultural production; in already humid areas the extra rainfall may, humid areas the extra rainfall may, however, impair adequate crop however, impair adequate crop drying and storage; drying and storage;

The extra precipitation predicted to The extra precipitation predicted to occur in some regions provides occur in some regions provides possibilities for off-site extra storage in possibilities for off-site extra storage in rivers, lakes and artificial reservoirs rivers, lakes and artificial reservoirs (on-farm or at sub catchment level) for (on-farm or at sub catchment level) for the benefit of improved rural water the benefit of improved rural water supply and expanded or more intensive supply and expanded or more intensive irrigated agriculture and inland irrigated agriculture and inland fisheries: fisheries:

The effects on water resources and The effects on water resources and water apportioning of international water apportioning of international river and lake basins can be very river and lake basins can be very substantial, with political overtonessubstantial, with political overtones

Increased temperatures may lead to more Increased temperatures may lead to more decomposition of soil organic matter; decomposition of soil organic matter;

Increased plant growth due to the COIncreased plant growth due to the CO22 fertilization effect may cause other plant fertilization effect may cause other plant nutrients such as N and P to become in short nutrients such as N and P to become in short supply; however, COsupply; however, CO22 increase would increase would stimulate mycorrhizal activity (making soil stimulate mycorrhizal activity (making soil phosphorus more easily available), and also phosphorus more easily available), and also biological nitrogen fixation (whether or not biological nitrogen fixation (whether or not symbiotic). symbiotic).

Through increased root growth there would Through increased root growth there would be extra weathering of the substratum, hence be extra weathering of the substratum, hence a fresh supply of potassium and a fresh supply of potassium and micronutrients; micronutrients;

The COThe CO22 fertilization effect would fertilization effect would produce more litter of higher C/N ratio, produce more litter of higher C/N ratio, hence more organic matter for hence more organic matter for incorporation into the soil as humus; incorporation into the soil as humus; litter with high C/N decomposes slowly litter with high C/N decomposes slowly and this can act as a negative feedback and this can act as a negative feedback on nutrient availability; on nutrient availability;

the 'COthe 'CO22 anti-transpirant' effect would anti-transpirant' effect would stimulate plant growth in dryland areas, stimulate plant growth in dryland areas, and more soil protection against erosion and more soil protection against erosion and lower topsoil temperatures, leading and lower topsoil temperatures, leading to an 'anti-desertification effect'.to an 'anti-desertification effect'.

Global climate change, if it occurs, will Global climate change, if it occurs, will definitely affect agriculture. definitely affect agriculture.

Most mechanisms, and two-way Most mechanisms, and two-way interactions between agriculture and interactions between agriculture and climate, are known, even if not always climate, are known, even if not always well understood. well understood.

It is evident that the relationship It is evident that the relationship between climate change and between climate change and agriculture is still very much a matter agriculture is still very much a matter of conjecture with many uncertainties of conjecture with many uncertainties

it remains largely a conundrum. it remains largely a conundrum.

Major uncertainties affect both the Global Major uncertainties affect both the Global Circulation Models (GCMs) and the Circulation Models (GCMs) and the response of agriculture, as illustrated by response of agriculture, as illustrated by differences among models, especially as differences among models, especially as regards effects at the national and sub regards effects at the national and sub regional levels.regional levels.

In addition, many of the models do not In addition, many of the models do not take into consideration COtake into consideration CO22 fertilization fertilization and improved water-use efficiency, the and improved water-use efficiency, the effect of cloud cover (on both climate and effect of cloud cover (on both climate and photosynthesis), or the transient nature of photosynthesis), or the transient nature of climate change. climate change.

It is also worth remembering that It is also worth remembering that enormous knowledge gaps still affect enormous knowledge gaps still affect the carbon cycle (with a missing sink of the carbon cycle (with a missing sink of about 2 Gt of carbon), the factors about 2 Gt of carbon), the factors behind the recent near-stabilization of behind the recent near-stabilization of the atmospheric methane the atmospheric methane concentrations or the unexplained concentrations or the unexplained reduced rate of COreduced rate of CO22 increase in recent increase in recent years, the effect of volcanic eruptions years, the effect of volcanic eruptions (such as the recent Pinatubo eruption), (such as the recent Pinatubo eruption), the effect of any increased cloudiness, the effect of any increased cloudiness, etc. etc.

1. Describe with appropriate examples the uses of soils: a) in agricultural production

b) Non agricultural activities2. Explain briefly why soil information is

important for a country’s development.3. What is land degradation?4. State five sources of green house gases5. State five land qualities that constrain

agriculture6. Discuss the general issues of climate change

on agriculture

7. What is CO2 Fertilization effect?8. Discuss the effect of increased UVR on: a)

crops, b) animals, c) tropospheric ozone, d) rising temperatures

9. Discuss the ecological and indirect climate change effect on agriculture and the environment.

9. Discuss the principal types of land degradation.

COCO22 CHCH44 NN22O O

Atmospheric Atmospheric lifetime (yr) lifetime (yr)

120 120 14.5 14.5 120 120

Direct GWP Direct GWP 11 1 1 24.5 24.5 22 320 320

Pre-industrial Pre-industrial concentration concentration 33

280 ppmv 280 ppmv 0.8 ppmv 0.8 ppmv 288 ppbv 288 ppbv

Present-day levels Present-day levels 360 ppmv 360 ppmv 1.72 ppmv 1.72 ppmv 310 ppbv 310 ppbv

Current annual Current annual increase (%) increase (%)

0.5 0.5 0.9 0.9 0.25 0.25

Major agricultural Major agricultural sources sources 44

deforestation deforestation - wetland rice - wetland rice - synthetic N - synthetic N fertilizers fertilizers

- ruminants - ruminants - animal excreta - animal excreta

- biomass - biomass burning burning

- biological N - biological N fixation fixation

Percentage of Percentage of global source global source

stemming from stemming from agriculture agriculture

30 30 40 40 25 25

Predicted change Predicted change 1990-2020 1990-2020

- - + + + +

Continent Continent 1961-1990 exponential growth rate (%) 1961-1990 exponential growth rate (%)

Ruminant Ruminant numbers numbers

Forested Forested area area

Rice area Rice area Fertilizer Fertilizer consumption consumption

Africa 1.29 -0.43 2.23 6.21

N and C America

-0.07 -0.02 1.50 3.29

S. America 1.29 -0.49 1.65 9.15

Asia 1.18 -0.59 0.62 9.54

Europe 0.33 0.25 0.78 2.75

Oceania 0.07 -1.15 5.88 1.25

World 0.90 -0.26 0.74 5.35

Table 1.3. Growth rates between 1961 and 1990 in agricultural sectors responsible for greenhouse gas emissions (from FAO, 1990). Europe and Asia do not include the former USSR. Domestic ruminant numbers were computed as the sum of cattle, sheep, goats, camels and buffaloes

Figure 1.2. Schematic effect of CO2 concentrations on C3 and C4 plants (after Wolfe and Erickson, 1993). The main mechanism of CO2 fertilization is that it depresses photo-respiration, more so in C3 than in C4 plants

ETP: Evapotranspiration potential WHC: Soil water holding capacity

ETA: Actual evapotranspiration OM: Organic matter

WUE: Water-use efficiency LAI: Leaf area index

The heavy line indicates a hypothetical link between increased humidity and cloudiness.

Box 1.2. Some mechanisms likely to affect biomass production under global change conditions. Note that the ratio between economic yield (e.g., grain, fibre) and biomass may change relative to current conditions

1985: Global Flood Archive – Dartmouth 1985: Global Flood Archive – Dartmouth ObservatoryObservatory