If farmers think they have a tough time producing enough rice, wheat and other grain crops, global warming is going to present a whole new world of challenges in the race to produce more food, scientists say.
In a warmer world beset by greater extremes of droughts and floods, farmers will have to change crop management practices, grow tougher plant varieties and be prepared for constant change in the way they operate, scientists say.
"There certainly are going to be lots of challenges in the future. Temperature is one of them, water is another," said Lisa Ainsworth, a molecular biologist with the US Department of Agriculture.
Spiraling grain prices in recent months have startled governments long used to affordable rice, wheat, soy and maize.
But rising demand and likely greater climate variability and more fluctuations in crop output could mean even more uncertainty for prices.
Current estimates suggest demand for cereals will jump by more than 50 per cent by 2050 as the world's population rises from 6.6 billion to about nine billion.
The world has already warmed by about 0.7 degrees Celsius on average since the 1800s and studies show higher temperatures can cut yields, particularly in the tropics where a lot of rice is grown.
"In northeastern China, low temperatures, a short growing season and lack of water limit production, so rising temperatures in the future may have beneficial impacts there," said Dr Ainsworth.
"However, in the southern parts of the country, higher temperatures will likely cause yield losses," she told Reuters.
Pollution is another threat. Ozone, which is produced at ground-level by sunlight interacting with pollution from burning fossil fuels, can cut plant productivity. The higher the ozone levels, the worse the damage.
In the northern hemisphere, ozone is a growing problem and is estimated to cost farmers billions of dollars in lost production.
"In the major rice-growing regions, which are India and China, ground-level ozone concentrations even today are very high and certainly exceed the threshold for damage. Ozone is already decreasing yield potential in many areas," Dr Ainsworth said.
Rice is grown in more than 100 countries. More than half the world's population rely on it as their main food source.
A major UN climate panel report last year said in low-latitude regions, even moderate temperature rises of between one and two degrees Celsius could trim crop yields. In cooler mid to high-latitude regions, localised increases up to three degrees Celsius plus higher amounts of carbon dioxide in the air could be beneficial to yields, provided there was enough water.
But anything beyond three degrees locally would be bad for crop yields, said the panel's Fourth Assessment Report on the impacts of climate change, which drew on the expertise of hundreds of scientists from around the world. Studies show that higher carbon dioxide levels, on their own, can boost rice and wheat production but any benefit is negated by the stress caused by higher temperatures, lack of water from changes in rainfall patterns and pollution.
Plants breathe in CO2 to make sugars and other complex compounds grow. Carbon dioxide levels from burning fossil fuels are rising rapidly and are now the highest than at any time in the past 650,000 years.