Climate Change and Agricultural Productivity

In my last post, we explored the link between health and food security. What we’ve found so far is that food security is essential for maintaining a healthy population. In particular, food accessibility is so integral.

However, the food production network is not limited to solely growing the food, but also includes human capital, such as roads and storage. And as a whole, the food system is vulnerable as soon as even one component of food security is threatened.  The earth is projected to become warmer and wetter; however, this change will probably not be gradual changes, but instead as more frequent, longer, and intense hotspells and rain which will affect the different components of the food system. In this post, I will be exploring how climate affects agricultural productivity and in particular, will be mainly looking at temperature, CO2, and precipitation.

Temperature and agricultural productivity

With higher seasonal temperatures can influence agricultural productivity and food security. Due to warming, it is predicted that crops such as cereals and soya beans will benefit as their range and productivity will increase northwards. The warming Earth could mean a 30% increase in yields by 2050 for some crops. With added technological advancement, we could see a possible 37 to 101% increase in wheat yield by 2050 in Europe.

However, for some regions such as the tropics with temperatures already reaching the physiological maxima, evaporation rates will increase due to high heat stress. Extreme temperatures and precipitation which may hinder crop growth. A 2 degree increase may mean increase in yields for mid-latitudes whereas in the lower latitudes may mean a 10% decrease, as shown in Figure 1 .

Figure 1 Sensitivity of different crops (maize, wheat, and rice from mid- to high-latitudes vs low latitudes) to temperature change (Source)

Atmospheric Change and Agricultural Productivity

Increase in CO2 can affect photosynthesis and transpiration, and two different photosynthetic pathways show different crop yields. There are different types of plants with different levels of photosynthetic efficiency. Plants that undergo C3 pathways of photosynthesis have lower efficiency compared to plants that undergo C4 photosynthesis. The majority of plants and crop plants are C3 (wheat, rice, etc.), whereas the C4 pathway plants (such as maize and sugar cane) can be seen as an evolution of C3 to C4 in hot and sunny regions with soil moisture limitations. C3 plants are limited by carbon dioxide, and tend to fare well in cooler temperatures, whereas C4 plants thrive off CO2 (Figure 2). So you could argue that C4 will benefit from global warming.

Figure 2 CO2 on C3 and C4 plants (Source)

The ‘greenhouse fertilization effect’ details the effect where due to the increase of CO2 in the atmosphere, there will be increased plant growth, thus C3 plants may grow bigger quickly compared to C4 despite photosynthesizing more efficiently. However, this greenhouse fertilization effect can be counteracted by other climate change outcomes such as temperature, water, and nutrient restraints. Every plant has an optimum for these different factors, and when they have been surpassed, this may mean that crops will not grow as efficiently. However, an increase in CO2 is not necessarily great for crop production as it decreases its nutritional value, which directly threatens human health. 

Higher CO2 levels have been linked with reduced quality in alfalfa and soybean plants as they decrease in protein and nitrogen content. This has further implications on livestock support, which threatens food production. Additionally, although C4 pathways were more prominent during the Ice Age with low humidity and low carbon dioxide levels, increased CO2 showed that C3 plants fare better in terms of yield.

Figure 3 Graph showing change in yield for the 2020s, 2050s, and 2080s (compared to 1990s) with and without CO2 effects (Source)

Figure 3 shows that Europe and North America will benefit (albeit for a short time) from climate change, whilst most countries will show general decrease in yields. Therefore decreasing CO2 concentrations in the atmosphere may be the best way forward to save our agricultural yields. For example, Arnell et al. suggests that minimizing CO2 to 550ppm may soften the production loss.

To conclude this post, it is evident that temperature and CO2 have impacts on agricultural productivity. It's also quite evident that there's going to be a slight imbalance in impact around the world. In my next post, I'm thinking of expanding on other factors that influence agricultural productivity (such as water, pests, extreme events.)

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