How Assam's tea is beginning to feel the strain of global warming

Lush green tea plantations, so bright they often look fluorescent, blanket the hills of Assam in northeastern India. Women plucking the leaves in black aprons with large baskets on their backs dot the gardens that contribute to India's production of nearly a third of the world's tea. But this picturesque industry that the British began in the early 19th-century faces a very modern problem: climate change.

Researchers and planters worry that a rise in temperatures and change in rainfall patterns are threatening the production and quality of Assam's famous tea.

About 850 tea gardens in Assam produce 55 percent of India's tea, but crop yields are decreasing and amid fears of a correlation with environmental change. Production in the state fell from 564,000 tons in 2007 to 487,000 tons in 2009, and the crop was estimated to have fallen to 460,000 tons in 2010, according to the Assam Branch Indian Tea Association. "Climate changing is definitely happening," said Mridul Hazarika, the director of the Tea Research Association, which is conducting studies on how the changes are hitting tea production. "It is affecting the tea gardens in a number of ways."

In the tea-growing areas of Assam, average temperatures have risen 2C and rainfall has fallen by more than a fifth in the past 80 years. Globally, 2010 was the hottest year on record, according to temperature readings by Nasa's Goddard Institute of Space Studies. An increase in temperatures affects the ability of the plant to grow, Hazarika said.

Tea planters have also noticed that the change in winter temperatures has affected the dormancy period of their plants. Prabhat Bezboruah, a tea planter based in Jorhat, Assam, said that 10 years ago winter temperatures dropped to around 4C or 5C, but the temperature in his region this winter has not gone below 9C. "We're used to seeing everything shut down," he said. "Now what's happening is we're not getting a dormancy. There is still some leaf on the bush."

Mr Bezboruah said the planters must wait and see what result this will have on next year's crop. Another environmental problem for the gardens has been an increase in erratic weather. Weather extremes cause additional stress to the plants, which they have not previously had to deal with, Mr Hazarika said. This stress could affect the bushes' production levels.

April and May saw an unusually high rainfall in the tea-growing areas. The wet and humid conditions led to an explosion in the population of a tropical plant pest.

"When there is a lot of rain and a lot of dampness, certain kinds of insects thrive in tea," said Dhiraj Kakati, the secretary of the Assam Branch Indian Tea Association. He added that no conclusive evidence as of yet has proven that climate change caused this high rainfall or production loss.

Many tea gardens suffered a huge loss from these pests because they did not use aggressive methods to kill the insects. The gardens export their crops and did not use pesticides that are restricted because of environmental concerns, Kakati said.

In addition to the indirect impact on the plants via the pests, last year's excessive rainfall directly hurt the crops because it led to more hours of overcast skies and less sunlight and oxygen, according to Mr Hazarika. His organisation's research found that Assam experienced an average of an hour less of sunshine each day during this past growing season.

There is also a fear among researchers and planters that environmental changes will affect the quality of the tea by weakening its powerful taste.

"We are indeed concerned," Rajib Barooah, another tea planter in Jorhat, told the Associated Press. "Assam tea's strong flavour is its hallmark."