Many people living in the Eastern Himalayas — particularly those at higher elevations — are noticing signs of climate change, including warmer weather and less snow, according to a survey.

The Himalayas, the world's tallest mountain range, are home to more than 750 million people, and at least twice that number live in the river basins that get their water from the Himalayas' 15,000+ glaciers. Despite the immense probable impacts of climate change in the region, the extent and consequences are not well known, says Kamaljit Bawa, a conservation biologist at the University of Massachusetts in Boston. “There are predictions and guesses, but no real data,” he says.

To help fill in the blanks, Bawa and his colleague Pashupati Chaudhary decided to gather local environmental knowledge. They surveyed 250 households in 18 villages in West Bengal, India and eastern Nepal, which are home to indigenous populations including Sherpa (Biol. Lett. doi:10.1098/rsbl.2011.0269; 2011). Because these villagers make their living off the land, they're intimately in tune with their surroundings, explains Bawa. “It's very cold there and it's often raining, so they're talking about the weather all of the time,” he adds.

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The researchers found nine different indicators of climate change that were reported by a two-thirds majority of respondents in one or more villages. Overall, about 73% of the respondents believe that the weather is getting warmer, 67% believe that summer starts earlier now than it did a decade ago, and nearly 70% believe that the monsoon season starts earlier. About 46% believe that there is less snow on the mountains than in previous years, and 70% believe that local sources of water are drying up. More than 53% of respondents reported substantially earlier budding in several species of plants, and almost 49% reported earlier flowering. On average, 54% reported seeing new crop pests in their villages in recent years, and 46% reported seeing mosquitoes for the first time.

When the researchers divided the villages into two categories — those lying between 1,000 and 2,000 metres elevation, and those between 2,000 and 3,000 metres — they found some dramatic differences between the groups. Although more than 77% of higher-altitude residents reported that summer had begun earlier in recent years, less than 58% of those living at lower altitudes reported the same. And although more than 75% of the respondents at higher altitudes reported finding new crop pests in recent years, only 33% of those living at lower altitudes did.

The results, Bawa says, are consistent with trends predicted by climate models and other studies. One study has reported a temperature rise of 0.01 to 0.04 °C per year in the Eastern Himalayas from January to March, and, in general, temperature rise from climate change is happening more quickly at high altitudes.

The researchers say the findings could provide a jump-start for other scientists seeking to test specific climate hypotheses in a region where scientific data are meagre at best.