The worldwide production of rice accounts for more greenhouse gas emissions (GHG) in total than that of any other plant food. It was estimated in 2021 to be responsible for 30% of agricultural methane emissions and 11% of agricultural nitrous oxide emissions. Methane release is caused by long-term flooding of rice fields, inhibiting the soil from absorbing atmospheric oxygen, a process causing anaerobic fermentation of organic matter in the soil. A 2021 study estimated that rice contributed 2 billion tonnes of anthropogenic greenhouse gases in 2010, of the 47 billion total. The study added up GHG emissions from the entire lifecycle, including production, transportation, and consumption, and compared the global totals of different foods. The total for rice was half the total for beef.
A 2010 study found that, as a result of rising temperatures and decreasing solar radiation during the later years of the 20th century, the rice yield growth rate has decreased in many parts of Asia, compared to what would have been observed had the temperature and solar radiation trends not occurred. The yield growth rate had fallen 10–20% at some locations. The study was based on records from 227 farms in Thailand, Vietnam, Nepal, India, China, Bangladesh, and Pakistan. The mechanism of this falling yield was not clear, but might involve increased respiration during warm nights, which expends energy without being able to photosynthesize. More detailed analysis of rice yields by the International Rice Research Institute forecast 20% reduction in yields in Asia per degree Celsius of temperature rise. Rice becomes sterile if exposed to temperatures above 35 °C (95 °F) for more than one hour during flowering and consequently produces no grain.
Read more, here.