NAIROBI, Kenya — From ancient ruins in Thailand to a 12th-century settlement off Africa’s eastern coast, prized sites around the world have withstood centuries of wars, looting, and natural disasters. But specialists say they might not survive a more recent menace: a swiftly warming planet.

“Our world is changing, there is no going back,” Tom Downing of the Stockholm Environment Institute said yesterday at the U.N. climate conference, where he released a report on threats to archaeological sites, coastal areas, and other treasures.

Recent floods attributed to climate change have damaged the 600-year-old ruins of Sukhothai in northern Thailand, the report said, while increasing temperatures are “bleaching” the Belize barrier reef and a rising sea level is sending damaging salt into the wetlands of Donana National Park in Spain.

Mr. Downing also said the ocean could eventually engulf ancient settlements such as the Old City on Kenya’s Lamu island, which dates to the 12th century and has been named a UNESCO World Heritage site.

Lamu is vital to Africa’s history; Omani Arab sultans who ruled the eastern coast of the continent first settled there before moving to Zanzibar. They left behind winding alleyways and an unspoiled 8-mile-long sandy beach that now attracts tourists to Lamu.

Thailand’s ruins of Sukhothai — which means “dawn of happiness” — include artifacts from ancient royal palaces, Buddhist temples, and city gates. Founded in 1238, Sukhothai was once capital of a Thai kingdom.

“Some of the developments we are faced with mean the parks of today may not be relevant tomorrow,” executive director of the U.N. Environment Program, Achim Steiner, said. “Adaptation to climate change should and must include natural and culturally important sites.”

He said the response cannot be to simply “lock things up in museums and zoos.” Instead, he said, governments worldwide must act to stem global warming. Scientists attribute the past century’s 1-degree rise in average global temperatures at least in part to the accumulation of carbon dioxide, methane, and other greenhouse gases in the atmosphere — byproducts of power plants, automobiles, and other fossil fuel-burning sources. Continued global warming will lead to shifts in climate zones, seas rising from heat expansion and runoff from melted land ice, and more extreme weather, scientists say.

The two-week climate conference, which started Monday, has drawn delegates from around the world to address climate change. The 189 parties to the 1992 U.N. climate treaty are divided into two groups: the 165 that ratified the treaty’s 1997 Kyoto Protocol mandating cutbacks in greenhouse gases, and a handful of others, led by America, that did not.

Under the Kyoto accord, 35 industrial countries are obliged to reduce their emissions by 5% below 1990 levels by 2012. President Bush rejected the Kyoto Protocol in 2001, saying it would hamstring the American economy and that it excluded poorer countries from its mandates.