Why does climate warming lead to reduced grain production?

Global warming will make the world's major grain belts expand to the polar regions. The expansion speed is 1℃ for every increase in the annual average temperature, the crops in the mid-latitude areas in the northern hemisphere will push northward 150 km -200 km, which will prolong the growth period of crops in the colder high-latitude areas and increase the output accordingly. However, rising temperature will also increase extreme weather in mid-latitude areas, increase surface evaporation, lower groundwater level and aggravate drought. Rising temperature will aggravate high temperature and summer drought in low latitudes. All these will lead to a decline in grain production in the middle and low latitudes. The main grain producing areas in the world are all distributed in the middle and low latitudes, and the cultivated land area in the high latitudes is limited, so the increased grain output in the high latitudes is far from making up for the reduced grain output in other regions.

In addition, climate warming will not only aggravate land desertification, but also multiply agricultural pests and diseases, so the harm to crops will also increase.

Climate warming will also lead to rising sea level, backward flow of seawater and inland expansion of saline soil, which will make the salinization and swamping of crop growing areas more serious, reduce the planting area in coastal areas and reduce the grain yield.

As for the impact of increasing carbon dioxide on increasing food production, it is extremely limited. It is true that carbon dioxide is an important raw material for green plants to carry out photosynthesis and make organic matter, but it is not the only raw material. Although carbon dioxide has a positive effect on plant growth, it is often affected by sunlight, moisture and nutrients, which greatly reduces this positive effect. Generally speaking, the content of carbon dioxide in the atmosphere has basically reached the "on-demand" level of plant photosynthesis, and it is empty to increase it again.