The ancient capital in western Japan was the venue for negotiations in 1997 that drafted the Kyoto Protocol, the landmark UN treaty that for the first time legally requires cuts in carbon emissions blamed for global warming.
But long before the treaty, Kyoto was also known for another sort of greenery -- a landscape studded with hundreds of historic temples, shrines and castles where the gardens are said to be in harmony with each season.
At Tenryu-ji temple, listed as a World Heritage site, the gates close to tourists at twilight to allow the Zen monks meditate in front of the garden to try to conquer their worldly desires.
"It's not an exaggeration to say that gardens represent the beauty of Kyoto," said Josho Toga, head priest of the 14th-century temple in the Arashiyama hills on Kyoto's outskirts. "And moss is indispensable for the gardens."
Toga, wearing a grey monk's robe, pointed to the moss in the traditional "sansui" garden that had turned from watery green to dark brown.
"The moss is in danger as recent changes to the climate have visibly damaged it," Toga said.
"Nature is honest," he continued. "It moves with the subtle changes in the surroundings and moss in particular is sensitive."
More than 100 kinds of moss are growing at Tenryu-ji, forming a green carpet against white sand that looks like ripples of water flowing around the arranged rocks.
Kyoto in recent years has rarely had drizzling rain, which produces the mist that allows moss to grow, said Nobuyuki Hiraki, chief landscaper at the Stone Gardening firm in charge of preserving gardens at Tenryu-ji and other major temples.
"Once part of nature begins to be destroyed, it can disappear instantly," he said. "I'm afraid that Kyoto will no longer be Kyoto in, say, 100 years."
According to a survey covering 13 of Kyoto's 17 designated World Heritage sites, nine said the moss in their gardens was not growing well compared with 10 years ago.
Eight of them felt "a strong sense of fear" for the moss due to higher temperatures, less precipitation and air pollution, the poll showed.
Yoshitaka Oishi, a moss researcher at Kyoto University who conducted the survey early this year, pinned the blame on global warming.
Average temperatures in the city have increased by more than two degrees Celsius over 70 years, while drizzling rain was recorded merely once or twice a year over the past decade, compared with some 70 days in the early 1960s, Oishi said.
Many temples in Kyoto have even turned to bringing in moss from other places, Oishi said.
"But that's not the right solution," he said. "We would lose an important part of Japanese culture if we fail to take special care of moss."
But the damage would be more than symbolic.
Some 48 million tourists, mostly domestic, flock to Kyoto each year, spending 637 billion yen (six billion dollars), according to city officials.
Kyoto, home of the imperial family for more than a century until they moved to Tokyo in 1869, was the birthplace of many aspects of Japanese culture -- the tea ceremony, flower arrangement, kimonos, kabuki theatre and geishas.
"The landscape and nature in Kyoto are valuable assets for the Kyoto economy," said Katsuhito Nakano, chief analyst at Kyoto Research Institute Inc., a research unit with the Bank of Kyoto.
"People in Kyoto are serious about the environment as they feel responsible as the home of the Protocol, but climate change cannot be resolved only by Kyoto," Kanano said.
Japan, whose economy is recovering from recession in the 1990s, is far behind in meeting its obligations under the Kyoto Protocol, which is boycotted by the United States and makes no demands of developing nations.
Autumn colours, another scenic attraction in Kyoto, have also been hit by climate change, researchers say, with leaves turning dull rather than becoming bright red.
"Kyoto represents Japan. It's an important part of our country's heritage," said Sayuri Kizawa, a 29-year-old nurse visiting from central Japan. "I think it's our duty to maintain Kyoto."
Toga, the head priest at Tenryu-ji, said it was not only tourists who would suffer a loss.
"The garden is not originally for tourists. It used to be and still is a place for meditation," Toga said. "A garden is a small universe."