July 6 (Bloomberg) -- Tea pickers in India, coffee-bean harvesters in Vietnam and millions of outdoor workers will be less productive because of rising temperatures from global warming, according to a study.

People working outside in Delhi, for example, may suffer a 30 percent drop in productivity in the coming decades should temperatures continue climbing, Australian National University researcher Tord Kjellstrom said today in a report for Oxfam.

Residents of tropical countries and cities are likely to be hurt, especially if temperatures rise as much as 10 degrees Celsius (18 degrees Fahrenheit) above current conditions, the Oxfam report said. Temperatures that surpass 35 degrees Celsius, or 95 degrees Fahrenheit, stress manual laborers, affect productivity and ultimately their income, the study said.

Mortality rates in Delhi rise by as much as 4 percent, and 6 percent in Bangkok, with every 1 degree boost in temperature, according to Oxfam, a U.K.-based anti-poverty group. The 2003 summer heatwave in Europe resulted in 35,000 deaths, many of them in France, after temperatures rose 5 degrees above normal.

The U.S., Canada and other G-8 members meet this week in Italy to discuss ways wealthier nations can support greenhouse- gas cuts in developing countries without harming economic growth. Developing countries such as India want industrialized countries to contribute financing and technology to help them adapt to hotter weather, drought and rising seas.

Tea production in India, the world’s largest grower, fell 10 percent in the five months through May after dry weather in the biggest growing region damaged the crop, the state-owned Tea Board said on July 3. Dry weather in northeastern India, which grows more than half of the nation’s tea crop, may cut output by at least 5 percent, officials said.

To contact the reporter on this story: Jeremy van Loon in Berlin at jvanloon@bloomberg.net.

Last Updated: July 6, 2009 07:38 EDT