Possible Benefits of Global Warming on Agriculture

Pros and Cons

Given the need for caution, it may still be possible to make a few general comments. With more carbon dioxide in the atmosphere, the rate of photosynthesis in most tropical plants will increase. Photosynthesis requires carbon dioxide, water, and sunlight in order to take place. The so-called C3 plants [all major tropical plants except corn (corn), sugar cane, and pineapple] could increase their production of biomass by up to 30 percent.

However, increased photosynthesis will also increase weed growth, which could limit the yields of certain edible plants.

Higher temperatures will lead to a greater rate of evaporation, as the hotter the air, the more water vapor it can contain. In some places, especially limestone islands, this could possibly lead to greater occurrence of droughts in low-lying areas, and the soil fertility could decline.

Higher temperatures and greater evaporation from ocean surfaces may lead to an increase in the air humidity. With greater air humidity and higher sea temperatures, there could be a greater frequency of severe cyclones during the cyclone season, and a possible lengthening of the cyclone season.

Warm temperatures and higher humidity may well lead generally to an increased cloud cover and greater rainfall. So, low-lying areas could be subjected to more flooding [by rain and the sea], soils will suffer greater leaching and loss of fertility, and the hotter, more humid conditions will favor the incubation of agricultural pests and diseases. However, greater rainfall will produce more rapid chemical weathering in the subsoil and parent material [rocks], so releasing more nutrients into the soil.

Higher temperatures and humidity will undoubtedly lead to greater heat stress for humans. Outdoor workers, in particular, will feel the heat more acutely, and probably be less efficient. Animals, too, will suffer from heat stress, and their reproductive abilities may decline.

On mountainous islands, increased temperatures should mean that the land can be cultivated to higher levels than at present. Places that are -300 meters high will experience similar temperatures to those found today at sea level. In Papua New Guinea, coffee will be grown at higher altitudes, on steeper slopes, and overall, the amount of productive agricultural land could increase by as much as 10 percent.

It is possible that warmer temperatures can lead to a shortening of the time needed for crops to ripen, and this might mean that fruit are smaller, with a lower overall yield.

Sea Level Changes

For all Pacific islanders, but especially for the atoll communities, the major threat of climate change lies in the prospect of sea level rise. For the many inhabitants of the low-lying islands, a maximum freeboard of two or possibly
three meters may inspire little confidence in the face of current sea level projections. The fact that as much as a quarter of their emergent altitude above the ocean is likely to disappear within the next century and, with a prospect of continuing inundation beyond that time scale, clearly represents a major threat to the sustainability of long-term occupation. The social and psychological pressures arising from this threat are difficult to overestimate. Whereas the major volcanic and rock-based islands which boast substantial topography, always have the escape route towards higher ground, this may not be an option for many atoll nations. But for these nations along with the others, in the short term at least, faced with the slowly rising mean sea level through perhaps two or three millimeters per year, there will be a slow period of adjustment. The coastal strip so greatly prized and productive, will become gradually narrower, albeit at a rate which will be scarcely noticeable. Gradually, social and legal provisions permitting, farmers will be persuaded to cultivate the steeper land behind the coast, at the cost of increased expenditure of energy and possibly in the face of soil erosion. The essential infrastructure of modern living, the ports, the airstrip, the roads will face constant repair and adjustment in the face of changing conditions and there will be increased competition for available land between the providers, such as the farmers, and the distributors, such as the service industries, not to mention the tourism industry on which many such nations rely for foreign exchange. Superimposed upon this burden of pressure is likely to be the threat to the long term future. Accommodation to mounting environmental degradation will be a major threat to national morale as the limitations to long term sustainability are realized.

Although we tend to consider sea level rise simply in terms of the encroaching mean sea level, it is necessary also to have in mind that sea level fluctuates in response to a wide spectrum of frequencies. If those who link global warming
with enhanced gradients in temperature and barometric pressure, prove to be correct so that we may be headed for more stormy times, then we would expect increased wind wave activity to attack the coastal structures adding to the
hazards of the coastal strip. Storm surge activity, raising sea level locally over a matter of hours due to wind transport and the piling-up of water in the shallow coastal zone, will add to the damage already caused by the slow inundation. The consequent result will most likely be expressed in terms of salinization of coastal agricultural land, coastal erosion and physical damage to the infrastructure. In the light of these prospects, gradual accommodation to the hazards of sea level rise will be that much more difficult.

Fresh Water Supplies

There is a particular feature of the island environment which makes it possible to sustain life, even on islands of small surface area. In fact the island acts as a fresh water reservoir, collecting the rain which falls on its surface and storing that fresh water underground. The concept of an underground lens of high quality fresh water floating above the intruding sea water at depth was covered in an earlier module of this series. Here it was explained that due to simple physical processes it follows that for every meter which the water table rises above sea level in its transact across the island, the boundary between fresh and saline water sinks forty meters below sea level, given hydrostatic conditions. Consequently below oceanic islands, even in the case of the atoll type which have little topography, there exists an enormous reservoir of the fresh water essential for flora, fauna and human life. This is a remarkable natural advantage which the island nations enjoy so that under normal circumstances, there is no great need for stringent regulation of water usage, especially in the case of the tropical Pacific islands where precipitation is plentiful. However, there is an associated danger from the same physical processes in the face of rising sea level. We are informed that sea level is likely to rise by about fifty centimeters in the next century. The danger then is that if the water table remains at an undisturbed level, the depth of the vertical thickness of the fresh water reservoir will be reduced by twenty meters. It
is likely that such a change will cause stress, and even if that change can be tolerated by adjustment to user practice, the question may then arise: "Will the same be true of the next 20- or 30- centimeter sea level rise?"

Already there are island communities which have already over-stressed their water resources and are facing the prospect of radical measures to source drinking water. Desalinization of sea water is a possible but expensive possibility, but it is important to remember that the total environment has to be considered. Will the coastal coconut palms, so entrenched in the island culture, be at risk? Will the visible coastal environment which attracts the tourist dollar be sustainable, and most of all what effects will be seen in the island agriculture? How long will it take before the people of Kiribati, Tuvalu, the Marshall Islands and the Tuamotus, who grow babai (taro) in deep pits so as to tap the fresh water lens, begin to notice that their water source is becoming brackish, and that their babai yields are suffering as a result?

Frequency of Tropical Cyclone

It has been stated that the scientific community remains uncertain as to the effect of global warming on the hydrological cycle so that forecasts of greatly increased precipitation, but more particularly a significant increase in the occurrence of extreme and stormy events are questionable. The scientists are still grappling with the problems of the aerosols and the role they play in the complex interactions within the climate model. There are still strong proponents of an inevitable increase in extreme events. Of all the meteorological phenomena, the Pacific islanders fear most the tropical cyclone which is difficult for the meteorological services to forecast and to track, although in the last decade or so the use of satellite remote sensing has done much to improve the position. However, if the pessimistic view prevails, and extreme events become more readily triggered by global warming, then the region may suffer from increased damage to the environment and the infrastructure of modern society, while both commercial and subsistence agriculture will be seriously affected. Enhanced salinization of the coastal zone will occur, trees like the coconut palm will be uprooted or otherwise damaged and unable to bear fruit for several years, meanwhile locally crops may be flattened, so affecting bananas and other tropical fruit trees, root crops such as yams, taro, manioc and sweet potato together with green vegetables. The fact that in general terms tropical cyclones tend to weave a somewhat narrow path of destruction, their effect would be mitigated by a greater sense of community insurance
whereby inter-island and inter-nation support would be forthcoming from neighboring community for the relief of the limited areas so damaged. Fortunately a sound basis for such a cooperative response already exists in the FORUM structure.

While enhancement of cyclone activity remains simply a possibility at this stage, there seems to be a stronger case for the prospect of a shift of the cyclone belt into higher latitudes as a natural consequence of global warming. The implication then is that communities previously inexperienced in the ravages of tropical cyclones will have to face this new threat.

Impacts of Climate Change on Health

The challenges to public health presented by climate change clearly demand international, regional and national attention, as the potential exists for health effects to spread across the concentrated populations inhabiting small islands as in the Pacific region.

Perhaps climate change presents a relatively new and important public health concern. The principle threat seems to arise from the two major impacts which have arisen frequently in this text:

Temperature elevation together with the assumed, but yet unproven, changes to the precipitation pattern.

Rising sea level due to the thermal expansion of the surface ocean, creating inroads into the coastal zone, and further concentrating the population within infection range.

As the impacts of change begin to materialize, perhaps in terms of increased frequency of heat waves and air pollution episodes, possibly also a higher incidence of extreme weather and coastal flooding and perhaps more stagnant water available for breeding insects and the like, then consequent health effects may emerge. The following are examples:

  • Infectious disease, particularly those classed as "vector borne." In the medical sense vector biome refers to diseases such as Malaria transmitted from one organism to another by insect or other agent.
  • Heat-related morbidity and even mortality
  • Given severe conditions possible malnutrition from a threatened food supply.
  • Perhaps even infra-structural damage from extreme weather events, threats to a quality water supply, impacting on public health.
  • Following ozone level depletion and the consequent increase in ambient ultraviolet radiation, there could be direct health impacts in terms of skin cancer, ocular diseases and crop damage.

In this module a more detailed discussion on Malaria will follow, but first here, as in all aspects of medicine, it is necessary to keep in mind that there are background factors of considerable influence inherent in that discipline quite separate from the physical environment of climate change. For example we are all aware of the rapid advance of medicine in the course of our own lifetime. Drugs, antibiotics, remarkable surgical procedures have shown remarkable advances, and will continue to push out the borders of life expectancy. While such progress is most comforting it is also necessary to acknowledge limiting factors. Already overuse and misuse of antibiotics has produced a resistance and immunity among the agents of disease in many cases. In certain cases there have developed new currently untreatable illnesses for similar reasons. Again, given the extended time scale of climate change, we have no means of assessment of the skills and efficiency of the present generation of the medical profession


The name itself comes from the Italian language and comprises two words [mala meaning bad and aria meaning air]. It was not until the very last years of the nineteenth century that the link was made with the mosquito. Initially malaria was thought to result from the gases released from swamps, which explains the above name and also another once current, namely 'marsh fever'. But then there also lives in the swamps the Anopheles mosquito among other insects and we now know that it is this mosquito which can pick up the parasite, Plasmodium, from the blood of an infected person and transfer that parasite to that of a healthy person. Although now not as widespread as formerly, due to the limitation of stagnant water residues and chemical sprays sometimes conducted from aircraft over large areas, malaria is still classed as perhaps the most prevalent 'vector-bome' disease. Malaria currently has a worldwide mortality about 2 million people a year, and may kill an additional million people annually as temperatures rise.

The mosquitoes live in almost all tropical and sub-tropical countries where temperatures are warm and humid. They breed in stagnant or still water such as swamps, lakes, pools, or even coconut shells, empty tins and discarded trees, wherever there is water in which to lay their eggs. How malaria began initially is difficult to explain but it is now known that it is perpetuated by the female Anopheles mosquito who feeds off the blood of an infected person, picks up the parasite and transmits this later to another, while similarly feeding off that second person's blood.

So much for the basic facts of malaria, but the relevant question now is: How will global warming affect the continuity of the transmission of malaria?

It is thought that female mosquitoes are smaller in warmer temperatures and they need more nourishment in order to produce eggs. At higher temperatures, the mosquito bites more often, and the bite is more likely to be infectious
as a result. Rises in temperature and rainfall would also most likely allow the malaria mosquitoes to survive in areas immediately surrounding their current distribution limits. In fact, there has already been some evidence to support this. For instance, a high latitude, malaria-free region (Highlands) in Papua New Guinea has recently experienced a large number of malaria cases following a period of record-setting high temperatures and rainfall.

The first point to make is that increased temperature alone is likely to lead to more frequent infection due to the increased activity of the mosquito. More bites means more risk. Then, as has been seen in the Papua New Guinea case the infectious organisms will probably survive over larger geographical areas. Again as rising sea levels impact upon island communities there is likely to be experienced a measure of competition for shrinking living space giving a more concentrated population in land where more opportunity for stagnant water to accumulate as precipitation increases as is expected by some. The scene seems to favor the mosquito cycle of bite and transmission.

Direct effects of the anticipated changes in global and regional temperature, precipitation, humidity and wind patterns resulting from human induced climate change are the factors which have an impact on the vector reproduction habits and on their longevity, and are associated with changes in vector density.

Indirect effects of climate change might also alter the distribution of the Anopheles mosquito. For example, changes in vegetation and agricultural practices which are mainly caused by temperature changes and trends in rainfall patterns may occur. An irrigated land, such as rice paddies, which provide a suitable breeding ground for a number of vectors, may show shifts in their spatial patterns. Another indirect effect of climate change is associated with the rise in sea level and the proliferation of areas of brackish [mixture of salt and pure water] water influences the availability of habitat and encourages species which prefer brackish water. The migration of certain mosquitoes to higher latitudes and altitudes can also be expected.

The influence which climate change is likely to exert on human populations may also play an important role in the dynamics of disease transmission. For example, the large-scale migration of populations from areas in which vector-bome disease are endemic into receptive areas, a movement induced by rural impoverishment, and inevitably influenced by the dynamics of climate change, including the effects of sea level rise on low-lying coastal area, will prove to be significant.

Impacts on Settlements and Migration

As described earlier, if the emission of greenhouse gases continues at its present rate, it is expected that the carbon dioxide content of the lower atmosphere will double from the pre-industrial concentration in the interval until the year 2100. In the Tropical Pacific, this is expected to increase the temperature by 2 degrees Celsius, and to cause a rise in sea levels of - 50 centimeters above present level. Other possible changes are increases in rainfall, and increased frequency of severe cyclones, although there is some caution expressed here.

With the exception of Papua New Guinea, and the large Melanesian islands such as Guadalcanal and Malaita (Solomon Islands), Santo (Vanuatu) and Viti Levu (Fiji), people on most of the Pacific islands live very close to the coast. On many of the high volcanic islands, the population is squeezed into a narrow coastal zone less than 1 km wide, while the interior of the island is rugged and uninhabited.

On the coral atolls of Micronesia and Polynesia, people live just a few meters from the seashore, generally on the lagoon or leeward side of the atoll.

All this means that Pacific island populations are some of the most vulnerable in the world to changes in climatic patterns and a rise in sea level.

There will be more discomfort for people living very close to the ocean and the following impacts on settlement and migration patterns are possible:


People living in low-lying coastal areas immediately adjacent to the coast are at greater risk from flooding due to storm surges, high tides and overflow of rivers. As sea level rises, their agricultural land is also more likely to be removed by wave erosion, and to suffer from waterlogging and salinization. Low coral atolls, where the highest point may only be 5 meters or less above mean sea level or less, are particularly vulnerable.

Urban Problems

Most towns in the South Pacific are built right on the coast, since they developed as ports and trading centers. Rises in sea level could interfere with the sewage systems in such towns, making it harder to dispose of human waste. The higher temperatures and higher humidity could bring greater discomfort to people working in the town, and many offices and buildings will need air conditioning, which is costly. Many towns would lose substantial parts of their urban areas through flooding, if sea level rises. For example, a rise of 1.5 meters would cause Apia, Samoa, to lose nearly 50 percent of its land, including its commercial and traditional center. Fig. 4.2 shows a town center of Apia and one may simply judge the consequences of sea level rise.

Increased Droughts

Low-lying and rain-shadow areas could be particularly affected. This could cause water supply problems in urban areas such as Lautoka, Port Vila and Port Moresby. Variations in rainfall patterns could also interfere with hydroelectric projects, such as the Monasavu scheme in Fiji.

On atolls, rising sea levels could cause a decline in the size and quality of the fresh water lens, making the atoll no longer habitable.

Greater Frequency of Cyclone

If there are more cyclones, coastal populations could suffer more damage to buildings, more frequent loss of power and water supplies, and contamination of water through flooded septic tanks and sewage systems. The solution is to construct stronger, specially-designed buildings, but many village people may not have access to the necessary finance.

Resettlement of Coastal Population in Other Areas

With a slow, steady rise in sea level, most atolls and some of the low-lying coastal areas of the high islands will become uninhabitable, perhaps not in the immediate future, but after several hundred years. Their inhabitants will be forced to move away to other places.

In Papua New Guinea, people living in the mangrove forests along the Gulf of Papua could lose their timber and sago palm resources, and as they do not have any land rights in inland areas, their re-settlement could cause problems.

For people living on the atolls of French Polynesia, Kiribati, Tuvalu, and Micronesia, migration may an only solution to be investigated. For example, some families from Tuvalu have already migrated to Niue which is an uplifted island in the Pacific with a small population of - 2000. In all cases, re-settlement will isolate people from their traditional lands, denying them their cultural heritage.

Impacts on Political and Economical Experience of the Pacific Region

Political and economical experience, or the social and economic development activities, refer to the individual and collective abilities of our communities to make decisions and implement them. This decision-making process will provide social and economic benefits and enhance the individual and collective abilities of the community. The effectiveness of the process is measured by how well it can cope with issues of development at increasing levels of difficulty.

Today the impacts of climate and climate changes are among the most important considerations in the political and economical experience or the social and economic development activities of the Pacific region.

These is now little doubt that some impacts have already been triggered or enhanced more by the consequences of human activities which took place within the last 200 years rather than by the natural climate cycles in the life of the planet, which normally takes place on a time scale of hundreds, thousands, or millions of years.

Because we are preparing these students to play an active role in the community's [local, national, and international] political and economic life, this, issue also merits the creation of opportunities whereby students can practice appropriate skills of making and implementing decisions as a group and playing active roles to effectively assist their community's efforts at resolving the impacts of climate change.

In the light of the predicted physical impacts of climate change, such as the flooding of low-lying islands and lowland areas; the possible increase in frequency of strong tropical cyclones; heavy rainfalls; etc, the following political and economical effects may take place in the region:

A significant increase in efforts to strengthen the abilities of local institutions and communities to deal effectively with climate change impacts together with other social and economic development issues.

A significant increase in the number of responsibilities and the degree of authority given to regional and international institutions and key national communities which are in better positions or are more capable to administer the affairs of island communities which will be socially and economically deprived by climate change impacts.

A significant increase of efforts to develop more effective systems of extracting and sharing resources and experiences within and between island states at all levels and especially in the provision of basic services for the masses of peoples who may migrate away from low-lying islands and lowland areas seem to be at higher risk from the impacts of sea level rise.

Poor Are Most Vulnerable

The predicted impacts of climate change in a worst case scenario could exacerbate hunger and poverty around the world. There may be a strongly negative impact on economic activity, particularly in the natural resources sector. People who are highly dependent on farming, fishing, or forestry might well see their livelihoods degraded by change in rainfall patterns, degraded soils, and impoverished forests and fishing grounds.

The poor would suffer most because they have fewer options for responding to climate change. For example, they would find it more difficult to change over to new crops and practices, to pump water or to irrigate, to extend their cultivable land, or to adopt more intensive fishing methods. These issues require expensive inputs such as machinery or energy. The urban poor particularly would be at risk. There could be a risk to food supply and trade, but then shelters and city infrastructure upon which they rely, may prove inadequate in changed and volatile weather conditions.

The most vulnerable among the poor would be the women and children. Because women tend to be less geographically and occupationally mobile than men. They would find it harder to escape from their debilitated farms and forests. Families might be disrupted as able-bodied men moved away. This possibility has been confirmed by the recent drought of 1997 in PNG where most of the victims are women and children. Children would also face a high level of risk from disease. The greater health risks would menace young and malnourished children, the ill, the old, and the unsheltered.

At the same time, mass migration may increase all over the world. If climate change has severe impacts, waves of refugees and immigrants would have to move from the most affected regions to those that are least vulnerable. The most likely movements would be from rural to already stressed urban areas. Consequently, displaced and impoverished populations would suffer an erosion of their cultural identity. The victims of climate change may have little choice but to adopt ecologically and socially unsustainable ways of living, especially when migrating to large metropolitan areas. The resulting disruption to their culture might create social and political problems.


The later sections of this module have painted a bleak picture of the future which we face. On the one hand this may be justified by the fact that all, and especially the policy-makers, should be aware of the worst case scenario of possibilities if the present inertia to accept the responsibility of harsh and rigorous remedial procedures is to be overcome. It would not be prudent to adopt the soft line that we might delay action until we are confident that the greenhouse mechanism is indeed real and present. Should this eventually be the position we would have lost very valuable time, and the desperate need would then be with us to adopt even harsher measures and we would have already committed the world to climate change, not to the year 2100 but continuing change for another century or two. This is a problem which is likely to affect us all, and we all will need to take a share of the remedial load, however strenuous that may be. The pessimistic picture will at least help to have the message accepted.

On the other hand we need ultimately to view climate change in its many ramifications from a realistic perspective. Pessimism can induce panic and thereby create quite inappropriate behavior. If our aim is for realism, it would be appropriate to consider the following points:

It is known that in the greenhouse case, we face the very difficult prospect of search for a small drift in several environmental parameters against much larger slowly fluctuating features which have been in existence throughout
geological time. We may be deceived, either way, in our estimates of man-made influences. Indeed some scientists stress that the existence of the greenhouse model still requires proof, although such seems to be an increasingly minority view with the passage of time. Options should be left open while currently accepting the pessimistic view as a necessary insurance against less likely possibilities.

It is known that real drift in the basic environmental variables has indeed been taking place. The problem is not a new one yet the publicity surrounding the greenhouse issue is certainly new. The evidence is that global mean surface temperature has increased by between 0.3 degrees Celsius and 0.6 degrees Celsius in the last one hundred years. For global sea level the evidence is that this has risen by between 10 and 25 centimeters in the same interval. While these changes have been taking place, all but a few environmental scientists have been completely unaware of these changes. Indeed the focus of fear during this period, and even within the scientific community, has been quite the opposite of global warming. The anxiety was directed towards the hazards of a possible cooling of climate. Now the best estimates of our fate over the next one hundred years is that possibly the gradient of the warming trend will increase by a factor of about 3.

There remain many uncertainties. This is not to say that science has failed us. In fact during the last decade there has been an enormous step in our understanding of the interaction of earth, ocean, and atmosphere. Perhaps more has been learned in this time than throughout earlier history. The facts are that the problems which we face in the mechanisms of greenhouse and global warming are immense and complex and defy ready solutions. In addition to earth and atmosphere, quite revolutionary views are emerging over the role of ocean circulation and its links with climate over long time scales of hundreds and thousands of years. Astronomical variability too, involving the earth's axis and changes in its orbit through the mean plane of the solar system, together with several other complex motions are seen to be relevant to the climate issue. Then there are the cyclical changes in the main heat engine of the sun which control the sun spot cycles and solar radiation in general and so on. But in spite of all t

Meanwhile equally good practice is to attempt to overcome the lack of good quality long time series of relevant data, so that future climate models will be better placed to tune their computations to the real facts and also so that such material will provide the evidence of the real trend taking place in the sensitive parameters. In the case of the Pacific Islands, the main source of concern by far is that threat of rising sea level. The initiative taken by the South Pacific Sea Level and climate monitoring project with the support of the Government of Australia, is a prime example of a focus upon real issues in a constructive manner.


The composition of the earth's atmosphere has changed and it is still changing. Most scientists are convinced that this will result in global warming. At present we do not know with any certainty what the changes will be on a regional basis or how quickly they will occur. But we can be assured that change will occur a time scale of years and decades rather than weeks and months.

We may be able to influence the speed of climate change by reducing greenhouse gas emissions. If we slow down the rate of climate change, we will be in a better position to plan ahead, be ready and even take advantage of some of the opportunities a changing climate will provide. International cooperation is essential to develop policies to reduce the production and release of greenhouse gases. Tough policies may also be required to deal with the effects of climate change. These should be aimed at minimizing the impact of such changes or adapting to the impact of changes.

More research is needed to better predict what will happen in any particular area and what the impact of the changes in those areas will be. Climate modeling with complex computer calculations will help us to discover what type of changes can be expected and so guide government, industry, farmers and naturalists on the best way to use resources. Some suggestions may be summarized as follows:

  • To encourage conservation of energy.
  • To switch from coal to oil to natural gas.
  • To use different sources of energy such as wind, tidal, solar, biomass or geothermal and where access is available to the deep ocean close offshore to perhaps use the great temperature and density gradients between deep and surface waters.
  • To use lighter cars with more efficient engines.
  • To make fossil fuels less available to the public.
  • To plant more trees so as to absorb carbon dioxide, and to combat rising salinity of surface soils.
  • To reduce or stop large scale deforestation.
  • To find, test and plant different strains of crops to match a possibly changing environment.