Climate change and crop production

How a changing climate affects crops

Climate change is a long-term change in average temperature, rainfall and other climate patterns. The main cause today is the rise in greenhouse gases (GHGs) that trap outgoing heat: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), chlorofluorocarbons (CFCs) and water vapour. Agriculture both suffers from and adds to it: flooded rice fields and ruminant animals release methane; nitrogen fertilisers release nitrous oxide; burning crop residues and fuel release CO₂.

Effects on crops:

• Higher temperature speeds up crop development and shortens the grain-filling period, lowering yield. Late-sown wheat suffers terminal heat stress.
• Elevated CO₂ can raise photosynthesis, especially in C₃ crops (wheat, rice, soybean), the "CO₂ fertilisation effect". C₄ crops (maize, sorghum, sugarcane) gain less because they already concentrate CO₂.
• Erratic rainfall, more droughts and floods, rising sea level and salt entry into coastal fields.
• New pest and disease patterns and changed pollination.

Adaptation includes heat- and drought-tolerant varieties, changed sowing dates, water harvesting, crop diversification and conservation agriculture. Mitigation includes better rice water management, efficient fertiliser use and avoiding residue burning.

Climate classification

• Köppen classified climates using temperature, rainfall and natural vegetation, with letter groups (A tropical, B dry, C warm temperate, D cold, E polar).
• Thornthwaite based his classification on precipitation effectiveness and moisture (water balance).

Key points

• Main GHGs: CO₂, CH₄, N₂O, CFCs, water vapour.
• Paddy fields and ruminants → methane; nitrogen fertilisers → nitrous oxide.
• C₃ crops benefit more from extra CO₂ than C₄ crops.
• Köppen: temperature, rainfall, vegetation; Thornthwaite: moisture/precipitation effectiveness.

Exam tips

Expect "source of methane", "C₃ vs C₄ response" and "basis of a classification" questions. Link each GHG to an agricultural source.

Common mistakes

• Thinking all crops benefit equally from higher CO₂.
• Believing higher temperature always increases yield; it usually shortens crop duration and lowers yield.