In the humid, lush region of Gauhati, where an important part of the world's breakfast is born, the evidence of climate change is – literally – a weak tea.

Growers in tropical Assam state, India's main tea growing region, say rising temperatures have led not only to a drop in production but to subtle, unwelcome changes in the flavour of their brews. The area in north-eastern India is the source of some of the finest black teas. Assam teas are notable for their heartiness, strength and body, and are often sold as "breakfast" teas.

"Earlier, we used to get a bright strong cup. Now it's not so," said LP Chaliha, a professional tea taster.

Rajib Barooah, a tea planter in Jorhat, Assam's main tea growing district, agreed that the potent taste of Assam tea has weakened. "We are indeed concerned," he said. "Assam tea's strong flavour is its hallmark."

Tea growers want the Indian government to fund studies to examine the flavour fallout from climate change.

Assam produces nearly 55% of the tea crop in India, a nation that accounts for 31% of global tea production. However, production has dipped significantly, and plantation owners fear it will drop further as temperatures rise and rainfall patterns change.

Assam produced 564,000 tons of tea in 2007, but slipped to 487,000 tons in 2009. The 2010 crop is estimated to be about 460,000 tons. The drop in production has squeezed consumers. Prices have gone up about 10% over the past year.

The tea industry employs about three million people across India.