By Chris Hogg
BBC News, Tokyo
In Japan government scientists are trying to find ways to reduce the impact of global warming on the country's rice crop.
Researchers study the effect of greenhouse gases on rice
There are fears that the extremes of temperature that some researchers are predicting could affect both the yield and the quality of rice, a staple of the Japanese diet.
Flowering grain crops like maize, wheat and rice are particularly vulnerable to changes in temperature.
Rice is believed to have been cultivated in Japan for more than 2,500 years.
Although people are eating less than they used to, on average each person here still eats more than a kilogramme a week.
Japan is getting warmer. In the last decade or so the country's annual average temperature has been between 0.2 and one degree higher than the average recorded in the last 30 years of the 20th Century.
Research being carried out by Japanese government scientists suggests that if this trend continues, rice yields and quality could suffer.
"Global warming can affect rice in many ways," says Toshihiro Hasegawa, a senior researcher at the National Institute of Agro-Environmental Sciences near Tokyo.
"The plant itself can be very sensitive to temperature at any time of the growth stages. But the most devastating effect can be seen in the late stage of the rice growth."
The pollination stage for rice can last as little as an hour. That is why extremes of heat can do such damage.
Experiments carried out in controlled conditions in laboratories suggest that if it is warmer than 36C pollination fails.
In reality out in a rice paddy there are other factors such as wind speed and direction or altitude which affect the process.
So it is difficult for scientists to be precise about how soon we might start to see this kind of problem, and how damaging the effects might be.
Susumu Matsumoto is afraid Japanese rice might lose its taste
So far, they say, the main effect of global warming on the rice crops has been changes to the appearance of some grains affected by very hot weather.
But they fear that if Japan continues to heat up people might start to notice a change in the taste of the rice too unless new methods can be employed to protect the plants from the sun's rays.
"It would be a shame if high quality Japanese rice was to lose its good taste due to the effects of global warming," says Junji Mori, a commuter making his way home at Tokyo's Shinbashi station.
"Some rice you get here is imported and you can tell immediately from its taste that it is not Japanese."
Another commuter, Susumu Matsumoto, agrees. "I'm worried that Japanese rice might not taste as good," he says.
Mr Hasegawa and his colleagues at the Institute are less concerned.
"Yes this is a really important problem," he says, "but Japan has more than a thousand varieties of rice and different strains of each one."
The scientists are now looking at which varieties would be most resistant to high temperatures.
They are examining whether different strains which flower at different times of day when the temperatures are likely to be lower could be the answer.
Mr Hasegawa is optimistic that a solution to the problem can be found.
But others are not so sure.
"How do they know how much time they have?" asks Prof Stephen Hesse from Chuo University.
"We don't really have any idea, except in general terms of how fast and how high temperatures will rise."
Professor Hesse says he welcomes the fact that the Japanese government is looking at the problem now, "but we don't know whether they have a five year window or a 25 year window to find a solution" he warns.
The scientists at the Institute have set up a research site in a field to try to create the effect of an increase in greenhouse gases.
Carbon dioxide (CO2) is sprayed over the area, the multiple pumps reacting to gusts of winds to ensure the greater levels of CO2 remain constant.
The rice growing underneath is compared to that growing a few metres away under normal conditions.
Scientists are also looking ways to reduce the amount of methane that builds up in paddy fields.
The carbon in soil when trapped under water used to irrigate the rice paddies is not converted to CO2 but to methane, said to have more than twenty times the greenhouse gas effect of carbon dioxide.
About a quarter of all methane produced in Japan comes from rice fields and the country needs to cut emissions.
"Many other industries have been aware of the need to control emissions in the past," says Toshihiro Hasegawa.
"In agriculture there was more focus on environmental concerns. But scientists can help farmers to change their behaviour. We need to take strong action."