take place on a global scale. Climate change affects agriculture in a number

of ways, including through changes in average temperatures, rainfall, and

climate extremes; changes in pests and diseases; changes in atmospheric carbon

dioxide and ground-level ozone concentrations; changes in the

nutritional quality of some foods; and changes in sea level.

Climate change is already affecting agriculture, with effects unevenly

distributed across the world. Future climate change will likely negatively

affect crop production in low latitude countries, while effects in northern

latitudes may be positive or negative. Climate change will probably increase

the risk of food insecurity for some vulnerable groups, such as the poor.

Agriculture contributes to climate change by anthropogenic emissions of

greenhouse gases, and by the conversion of non-agricultural land into

agricultural land. Agriculture, forestry and land-use change contributed around

20 to 25% to global annual emissions in 2010.

There are range of policies that can reduce the risk of negative climate

change impacts on agriculture, and to reduce GHG emissions from the

agriculture sector. Impact of climate change on agriculture

Despite technological advances, such as improved varieties, genetically modified

organisms, and irrigation systems, weather is still a key factor in

agricultural productivity, as well as soil properties and natural communities.

The effect of climate on agriculture is related to variabilities in local

climates rather than in global climate patterns. The Earth's average surface

temperature has increased by 1.5 °F since 1880. Consequently, agronomists

consider any assessment has to be individually consider each local area.

On the other hand, agricultural trade has grown in recent years, and now

provides significant amounts of food, on a national level to major importing

countries, as well as comfortable income to exporting ones. The international

aspect of trade and security in terms of food implies the need to also consider

the effects of climate change on a global scale.

A study published in Science suggests that, due to climate change, "southern

Africa could lose more than 30% of its main crop, maize, by 2030. In South Asia

losses of many regional staples, such as rice, millet and maize could top 10%".

The Intergovernmental Panel on Climate Change has produced several reports that

have assessed the scientific literature on climate change. The IPCC Third

Assessment Report, published in 2001, concluded that the poorest countries

would be hardest hit, with reductions in crop yields in most tropical and

sub-tropical regions due to decreased water availability, and new or changed

insect pest incidence. In Africa and Latin America many rainfed crops are

near their maximum temperature tolerance, so that yields are likely to

fall sharply for even small climate changes; falls in agricultural

productivity of up to 30% over the 21st century are projected. Marine life and

the fishing industry will also be severely affected in some places.

Climate change induced by increasing greenhouse gases is likely to affect

crops differently from region to region. For example, average crop yield is

expected to drop down to 50% in Pakistan according to the UKMO scenario whereas

corn production in Europe is expected to grow up to 25% in optimum hydrologic

conditions. More favourable effects on yield tend to

depend to a large extent on realization of the potentially beneficial effects of

carbon dioxide on crop growth and increase of efficiency in water use.

Decrease in potential yields is likely to be caused by shortening of the

growing period, decrease in water availability and poor vernalization.

In the long run, the climatic change could affect agriculture in several ways

productivity, in terms of quantity and quality of crops

agricultural practices, through changes of water use and agricultural inputs

such as herbicides, insecticides and fertilizers

environmental effects, in particular in relation of frequency and intensity of

soil drainage, soil erosion, reduction of crop diversity

rural space, through the loss and gain of cultivated lands, land speculation,

land renunciation, and hydraulic amenities.

adaptation, organisms may become more or less competitive, as well as humans may

develop urgency to develop more competitive organisms, such as flood

resistant or salt resistant varieties of rice.

They are large uncertainties to uncover, particularly because there is lack of

information on many specific local regions, and include the uncertainties

on magnitude of climate change, the effects of technological changes on

productivity, global food demands, and the numerous possibilities of

adaptation. Most agronomists believe that

agricultural production will be mostly affected by the severity and pace of

climate change, not so much by gradual trends in climate. If change is gradual,

there may be enough time for biota adjustment. Rapid climate change,

however, could harm agriculture in many countries, especially those that are

already suffering from rather poor soil and climate conditions, because there is

less time for optimum natural selection and adaption.

But much remains unknown about exactly how climate change may affect farming

and food security, in part because the role of farmer behaviour is poorly

captured by crop-climate models. For instance, Evan Fraser, a geographer at

the University of Guelph in Ontario Canada, has conducted a number of

studies that show that the socio-economic context of farming may

play a huge role in determining whether a drought has a major, or an

insignificant impact on crop production. In some cases, it seems that even minor

droughts have big impacts on food security, versus cases where even

relatively large weather-related problems were adapted to without much

hardship. Evan Fraser combines socio-economic models along with

climatic models to identify “vulnerability hotspots” One such study

has identified US maize production as particularly vulnerable to climate

change because it is expected to be exposed to worse droughts, but it does

not have the socio-economic conditions that suggest farmers will adapt to these

changing conditions. = Observed impacts =

So far, the effects of regional climate change on agriculture have been

relatively limited. Changes in crop phenology provide important evidence of

the response to recent regional climate change. Phenology is the study of

natural phenomena that recur periodically, and how these phenomena

relate to climate and seasonal changes. A significant advance in phenology has

been observed for agriculture and forestry in large parts of the Northern

Hemisphere. Droughts have been occurring more

frequently because of global warming and they are expected to become more

frequent and intense in Africa, southern Europe, the Middle East, most of the

Americas, Australia, and Southeast Asia. Their impacts are aggravated because of

increased water demand, population growth, urban expansion, and

environmental protection efforts in many areas. Droughts result in crop failures

and the loss of pasture grazing land for livestock.

= Projections = As part of the IPCC's Fourth Assessment

Report, Schneider et al. projected the potential future effects of climate

change on agriculture. With low to medium confidence, they concluded that

for about a 1 to 3 °C global mean temperature increase there would be

productivity decreases for some cereals in low latitudes, and productivity

increases in high latitudes. In the IPCC Fourth Assessment Report, "low

confidence" means that a particular finding has about a 2 out of 10 chance

of being correct, based on expert judgement. "Medium confidence" has about

a 5 out of 10 chance of being correct. Over the same time period, with medium

confidence, global production potential was projected to:

increase up to around 3 °C, very likely decrease above about 3 °C.

Most of the studies on global agriculture assessed by Schneider et al.

had not incorporated a number of critical factors, including changes in

extreme events, or the spread of pests and diseases. Studies had also not

considered the development of specific practices or technologies to aid

adaptation to climate change. The US National Research Council

assessed the literature on the effects of climate change on crop yields. US NRC

stressed the uncertainties in their projections of changes in crop yields.

Their central estimates of changes in crop yields are shown above. Actual

changes in yields may be above or below these central estimates. US NRC also

provided an estimated the "likely" range of changes in yields. "Likely" means a

greater than 67% chance of being correct, based on expert judgement. The

likely ranges are summarized in the image descriptions of the two graphs.

Food security The IPCC Fourth Assessment Report also

describes the impact of climate change on food security. Projections suggested

that there could be large decreases in hunger globally by 2080, compared to the

2006 level. Reductions in hunger were driven by projected social and economic

development. For reference, the Food and Agriculture Organization has estimated

that in 2006, the number of people undernourished globally was 820 million.

Three scenarios without climate change projected 100-130 million undernourished

by the year 2080, while another scenario without climate change projected 770

million undernourished. Based on an expert assessment of all of the

evidence, these projections were thought to have about a 5-in-10 chance of being

correct. The same set of greenhouse gas and

socio-economic scenarios were also used in projections that included the effects

of climate change. Including climate change, three scenarios projected

100-380 million undernourished by the year 2080, while another scenario with

climate change projected 740-1,300 million undernourished. These

projections were thought to have between a 2-in-10 and 5-in-10 chance of being

correct. Projections also suggested regional

changes in the global distribution of hunger. By 2080, sub-Saharan Africa may

overtake Asia as the world's most food-insecure region. This is mainly due

to projected social and economic changes, rather than climate change.

Individual studies Cline looked at how climate change might

affect agricultural productivity in the 2080s. His study assumes that no efforts

are made to reduce anthropogenic greenhouse gas emissions, leading to

global warming of 3.3 °C above the pre-industrial level. He concluded that

global agricultural productivity could be negatively affected by climate

change, with the worst effects in developing countries.

Lobell et al. assessed how climate change might affect 12 food-insecure

regions in 2030. The purpose of their analysis was to assess where adaptation

measures to climate change should be prioritized. They found that without

sufficient adaptation measures, South Asia and South Africa would likely

suffer negative impacts on several crops which are important to large food

insecure human populations. Battisti and Naylor looked at how

increased seasonal temperatures might affect agricultural productivity.

Projections by the IPCC suggest that with climate change, high seasonal

temperatures will become widespread, with the likelihood of extreme

temperatures increasing through the second-half of the 21st century.

Battisti and Naylor concluded that such changes could have very serious effects

on agriculture, particularly in the tropics. They suggest that major,

near-term, investments in adaptation measures could reduce these risks.