Global warming threatens Asian rice production: study

Yahoo News 9 Aug 10;

WASHINGTON (AFP) – Even modest rises in global temperatures will drive down rice production in Asia, the world's biggest grower of the cereal grain that millions of poor people depend on as a staple food, a study published Monday warned.

Researchers from the United States, the Philippines and the Rome-based Food and Agriculture Organization (FAO) looked at the impact of rising daily minimum and maximum temperatures on irrigated rice production between 1994-1999 in 227 fields in China, India, Indonesia, the Philippines, Thailand and Vietnam.

They found that the main culprit in cutting rice yields was higher daily minimum temperatures.

"As the daily minimum temperature increases, or as nights get hotter, rice yields drop," said Jarrod Welch of the University of California, San Diego, and lead author of the study published in the Proceedings of the National Academy of Sciences of the United States.

"Up to a point, higher daytime temperatures can increase rice yield but future yield losses caused by higher night-time temperatures will likely outweigh any such gains because temperatures are rising faster at night," Welch said.

Rising temperatures in the past 25 years have already cut rice yields at several key growing locations by 10-20 percent.

The loss in production is expected to get worse as temperatures rise further towards the middle of the century, said Welch.

"If daytime temperatures get too high, they also start to restrict rice yields, causing an additional loss in production," he said.

Rice is a key global crop, eaten by around three billion people a day. In Asia, it is a staple food to some 600 million people who are among the world's one billion poorest inhabitants, the study and FAO data show.

A decline in rice production will mean more people will slip into poverty and hunger, the authors of the study warned.

"If we cannot change our rice production methods or develop new rice strains that can withstand higher temperatures, there will be a loss in rice production over the next few decades as days and nights get hotter," said Welch.

Rice yields falling under global warming
Richard Black BBC News 9 Aug 10;

Global warming is cutting rice yields in many parts of Asia, according to research, with more declines to come.

Yields have fallen by 10-20% over the last 25 years in some locations.

The group of mainly US-based scientists studied records from 227 farms in six important rice-producing countries such as Thailand, Vietnam, India and China.

This is the latest in a line of studies to suggest that climate change will make it harder to feed the world's growing population by cutting yields.

In 2004, other researchers found that rice yields in the Philippines were dropping by 10% for every 1C increase in night-time temperature.

That finding, like others, came from experiments on a research station.

The latest data, by contrast, comes from working, fully-irrigated farms that grow "green revolution" crops, and span the rice-growing lands of Asia from the Indian state of Tamil Nadu to the outskirts of Shanghai.

Describing the findings, which are published in Proceedings of the National Academy of Sciences (PNAS), lead researcher Jarrod Welch said:

"We found that as the daily minimum temperature increases, or as nights get hotter, rice yields drop."

The mechanism involved is not clear but may involve rice plants having to respire more during warm nights, so expending more energy, without being able to photosynthesise.

By contrast, higher temperatures during the day were related to higher yields; but the effect was less than the yield-reducing impact of warmer nights.

However, if temperatures continue to rise as computer models of climate project, Mr Welch says hotter days will eventually begin to bring yields down.

"We see a benefit of [higher] daytime temperatures principally because we haven't seen a scenario where daytime temperatures cross over a threshold where they'd stop benefiting yields and start reducing them," he told BBC News.

"There have been some recent studies on US crops, in particular corn, that showed the drop-off after that threshold is substantial," said the University of California at San Diego researcher.

The 2007 assessment of climate impacts from the Intergovernmental Panel on Climate Change (IPCC) concluded that although a modest temperature rise could increase crop yields in some regions, for "temperature increases more than 3C, average impacts are stressful to all crops assessed and to all regions".

A study published at the begining of last year concluded that half of the world's population could face a climate-induced food crisis by 2100, with the most extreme summers of the last century becoming routine towards the end of this century.

Hotter nights threaten food security - rice at risk
Climate change temperature increases will affect rice yields
FAO 9 Aug 10;

9 August, 2010 - Production of rice — the world's most important crop for ensuring food security and addressing poverty — will be thwarted as temperatures increase in rice-growing areas with continued climate change, according to a new study by an international team of scientists.

The research team found evidence that the net impact of projected temperature increases will be to slow the growth of rice production in Asia. Rising temperatures during the past 25 years have already cut the yield growth rate by 10-20% in several locations.

Published today in the Proceedings of the National Academy of Sciences (PNAS) — a peer-reviewed, scientific journal from the United States — the report analyzed 6 years of data from 227 irrigated rice farms in six major rice-growing countries in Asia, which produces more than 90% of the world's rice.

"We found that as the daily minimum temperature increases, or as nights get hotter, rice yields drop," said Mr. Jarrod Welch, lead author of the report and graduate student of economics at the University of California at San Diego (UCSD).

This is the first study to assess the impact of both daily maximum and minimum temperatures on irrigated rice production in farmer-managed rice fields in tropical and subtropical regions of Asia.

"Our study is unique because it uses data collected in farmers' fields, under real-world conditions," said Mr. Welch. "This is an important addition to what we already know from controlled experiments."

"Farmers can be expected to adapt to changing conditions, so real-world circumstances, and therefore outcomes, might differ from those in controlled experimental settings," he added.

Around three billion people eat rice every day, and more than 60% of the world's one billion poorest and undernourished people who live in Asia depend on rice as their staple food. A decline in rice production will mean more people will slip into poverty and hunger, the researchers said.

"Up to a point, higher day-time temperatures can increase rice yield, but future yield losses caused by higher night-time temperatures will likely outweigh any such gains because temperatures are rising faster at night," said Mr. Welch. "And if day-time temperatures get too high, they too start to restrict rice yields, causing an additional loss in production."

"If we cannot change our rice production methods or develop new rice strains that can withstand higher temperatures, there will be a loss in rice production over the next few decades as days and nights get hotter. This will get increasingly worse as temperatures rise further towards the middle of the century," he added.

In addition to Welch, other members of the research team are Professors Jeffrey Vincent of Duke University and Maximilian Auffhammer of the University of California at Berkeley; Ms. Piedad Moya and Dr. Achim Dobermann of the International Rice Research Institute (IRRI); and Dr. David Dawe of the Food and Agriculture Organization (FAO) of the United Nations.