Impact on agricultureand foodsupply 167increases in temperature (2–3◦C) but decrease for larger temperature
rises.^39 In most tropical and subtropical regions, potential yields are pro-
jected to decrease for most increases in temperature; this is because
such crops are near their maximum temperature tolerance. Where there
is a large decrease in rainfall, tropical crop yields would be even
more adversely affected.
Taking the supply of food for the world as a whole, studies tend to
show that, with appropriate adaptation, the effect of climate change on
total global food supply is not likely to be large. However, none of them
have adequately taken into account the likely effect on food production of
climate extremes (especially of the incidence of drought), of increasingly
limited water availability or of other factors such as the integrity of the
world’s soils, which are currently being degraded at an alarming rate.^40
A serious issue exposed by the studies is that climate change is likely
to affect countries very differently. Production in developed countries
with relatively stable populations may increase,whereas that in many
developing countries (where large increases in population are occurring)
is likely to decline as a result of climate change. The disparity between
developed and developing nations will tend to become much larger,
as will the number of those at risk from hunger. The surplus of food in
developed countries is likely to increase, while developing countries will
face increasing deprivation as their declining food availabilitybecomes
much less able to provide for the needs of their increasing populations.
Such a situation will raise enormous problems, one of which will be
that of employment. Agriculture is the main source of employment in
developing countries; people need employment to be able to buy food.
With changing climate, as some agricultural regions shift, people will
tend to attempt to migrate to places where they might be employed in
agriculture. With the pressures of rising populations, such movement is
likely to be increasingly difficult and we can expect large numbers of
environmental refugees.
In looking to future needs, two activities that can be pursued now
are particularly important. Firstly, there is large need for technical ad-
vances in agriculture in developing countries requiring investment and
widespread local training. In particular, there needs to be continued de-
velopment of programmes for crop breeding and management, especially
in conditions of heat and drought. These can be immediately useful in the
improvement of productivity in marginal environments today. Secondly,
as was seen earlier when considering fresh water supplies, improvements
need to be made in the availability and management of water for irriga-
tion, especially in arid or semi-arid areas of the world.