Opinion: Ireland may be the world's most food secure nation, but how will expected changes in climate impact on our crops?

The recent Global Food Security Index compiled by the Economist Intelligence Unit classified Ireland as the world’s most food secure nation. The mild, wet climate in Ireland is generally favourable for plant growth and thus crop production, but irregular precipitation patterns mean that rain does not always fall when it is wanted. While 2017 was a good year for grass growth and therefore the Irish dairy industry, the wet weather in early autumn this year had the consequence that some farmers struggled to harvest their crops, especially in Donegal where extreme rainfall had devastating consequences.

In a future climate, there may be more winter rain, leading to an increased risk of flooding, especially in the west of Ireland. Flooding is a problem for plants because the roots need oxygen and oxygen diffusion is reduced in flooded soils. But excess rain is not the only problem Ireland may have in a future climate. Less summer rain can result in droughts in the south-east and therefore a requirement for irrigation of crops such as potato.

Overall, Ireland may suffer less severe consequences from climate change than other parts of the world, and some aspects of agriculture may even benefit in the future

In addition to altered rainfall patterns, increased temperature and the rising CO2 concentration that is responsible for this temperature increase influence plant growth. To predict the overall impact of climate change on plant growth, we need to understand better how plants function.

The rising CO2 concentration has a direct effect on plant growth as CO2 is used in photosynthesis, a process that enables plants produce the carbohydrates they need for growth using the energy from sunlight. At current levels, CO2 is not saturating, so future increases in CO2 could theoretically lead to higher rates of photosynthesis and plant growth through a CO2 fertilisation effect.

However, it has been shown that most crops acclimate to higher CO2 concentrations, and, as a consequence, the actual stimulation of photosynthesis is not as large as one may expect. In addition, increased photosynthesis does not necessarily translate into higher yield, as yield improvements also require enhanced growth of the part of the crop that we harvest, such as grains. More research is required to gain a better understanding of grain growth can be stimulated to achieve higher yield in future high CO2 conditions.

To some extent, high CO2 concentrations can protect plants from the impact of drought: Plants take up CO2 through pores in the leaves called stomata, but they also lose water in transpiration through these pores. In higher CO2 concentrations, plants can partially close their stomata and still take up enough CO2, which means that they lose less water through transpiration.

In Ireland, where droughts are expected to be moderate (at least in the near future), the positive effect of high CO2 concentrations may compensate in part for less summer rain. However, recent research has shown that this protective mechanism may no longer work in hotter and drier climates. Instead the plants overheat and the CO2 fertilisation effects may be wiped out.

As temperature rises, grass growth will increase

A small rise in temperature could have positive effects on Irish agriculture with higher spring temperatures increasing grassland productivity in Ireland. Research on grass growth by Teagasc has shown that little grass production occurs below five degrees C, as the plants simply shut down growth and preserve their resources rather than investing them in the production of new leaves.

As temperature rises, grass growth will increase until an optimum temperature of about 20-25°C is reached. Forage maize production is also expected to increase in a warmer Irish climate, whereas cereal yield may decline under more extreme climate change scenarios because of a shorter grain filling period.

While good for grass growth, milder winters could have negative effects on winter cereals and oilseeds. Winter crops require a prolonged period of low temperature in winter to flower in spring. This process, called vernalisation, may not be effective in very mild winters, which could result in the lack of flowering and crop failures. On the other hand, flowering of forage grasses in pastures is not desirable as it decreases the forage quality, and lack of vernalisation in warmer winters may reduce flowering and instead promote vegetative growth, which would be good for the dairy industry.

To predict the overall impact of climate change on plant growth, we need to understand better how plants function.

Overall, Ireland may suffer less severe consequences from climate change than other parts of the world, and some aspects of agriculture may even benefit in the immediate future. Food imports, on the other hand, may be threatened as agriculture in already hot and dry countries becomes increasingly unsustainable. Transpiration in plants leads to a high demand for water in crop production. For example, over 1000 litres of water are required to produce one kg of wheat and the water consumption for rice is about 5000 litres per kg. Due to this high water demand, crops in large parts of the world have to be irrigated. By importing irrigated crops from southern Europe, Asia and the USA, Ireland contributes to water deficit in these countries. In particular, the import of crops such as rice, grapes and almonds results in unsustainable water use in other parts or the world.

The severe impact of climate change on crop production in hot and dry climates, combined with population growth, is one of the main reasons why it is vital to reduce greenhouse gas emissions. In the context of global food security, it is therefore promising that CO2 emissions have stabilised in recent years, although the persistently high emissions mean that the atmospheric CO2 concentration will continue to rise. Worryingly, emissions of other greenhouse gases, chiefly methane, has increased globally. In Ireland, a third of greenhouse gas emissions originate from agriculture and within this category methane-producing ruminant animals (cows and sheep) are the largest contributors. While Ireland has international obligations to curb greenhouse gas emissions, it is also in Ireland’s own interest to help prevent more extreme climate change that would have a negative impact on Irish agriculture, e.g. through altered precipitation patterns and an increased frequency of extreme weather events.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ