Glaciers in at least one-third of World Heritage sites possessing them, including Yosemite National Park, will disappear by mid-century even if emissions are curbed, the U.N. Educational, Scientific and Cultural Organization warned in a new report Thursday.

Even if global warming is limited to just 1.5 degrees Celsius (2.7 degrees Fahrenheit), which now seems unlikely, all the glaciers in Yosemite and the ice patches in Yellowstone National Park, as well as the few glaciers left in Africa, will be lost.

Other glaciers can be saved only if greenhouse gas emissions “are drastically cut” and global warming is capped at 1.5 degrees Celsius, the Paris-based UNESCO warned in its report.

“This report is a call to action,” UNESCO Director-General Audrey Azoulay said in a statement and linked the report to United Nations Climate Change Conference, known as COP27, which is set to begin in Egypt next week. “COP27 will have a crucial role to help find solutions to this issue.”

About 50 of the organization’s more than 1,150 World Heritage sites have glaciers, which together constitute almost a tenth of the world’s glaciered area.

The almost 19,000 glaciers located at heritage sites are losing more than 60 billion tons of ice a year, which amounts to the annual water consumption of Spain and France combined, and accounts for about 5 percent of global sea-level rise, UNESCO said.

“Glaciers are retreating at an accelerated rate worldwide,” said Tales Carvalho Resende, a hydrology expert with UNESCO.

The organization described a “cycle of warming” in which the melting of glaciers causes the emergence of darker surfaces, which then absorb even more heat and speed up the retreat of ice.

Besides drastic cuts in emissions, the UNESCO report calls for better monitoring of glaciers and the use of early warning mechanisms to respond to natural disasters, including floods caused by bursting glacial lakes. Such floods have already cost thousands of lives and may have partly fueled Pakistan’s catastrophic inundations this year.

While there have been some local attempts to reduce melt rates — for example, by covering the ice with blankets — Carvalho Resende cautioned that scaling up those experiments “might be extremely challenging, because of costs but also because most glaciers are really difficult to access.”

Throughout history, glaciers have grown during very cold periods and shrunk when those stretches ended. The world’s last very cold period ended over 10,000 years ago, and some further natural melting was expected in Europe after the last “Little Ice Age” ended in the 19th century.

But as carbon dioxide emissions surged over the past century, human factors began to quicken what had been expected to be a gradual natural retreat. In Switzerland, glaciers lost a record 6 percent of their volume just this year.

While the additional melting has to some extent balanced out other impacts of climate change — for instance, preventing rivers from drying out despite heat waves — it is rapidly reaching a critical threshold, according to UNESCO.

In its report, the organization writes that the peak in meltwater may already have been passed on many smaller glaciers, where the water is now starting to dwindle.

If the trend continues, the organization warned, “little to no base flow will be available during the dryer periods.”

The changes are expected to have major ramifications for agriculture, biodiversity, and urban life. “Glaciers are crucial sources of life on Earth,” UNESCO wrote.

“They provide water resources to at least half of humanity,” said Carvalho Resende, who cautioned that the cultural losses would also be immense.

Around the world, global warming is exposing ancient artifacts faster than they can be saved by archaeologists.

“Some of these glaciers are sacred places, which are really important for Indigenous peoples and local communities,” he said.

UNESCO cited the example of the centuries-old Snow Star Festival in the Peruvian Andes, which has already been impacted by ice loss. Spiritual leaders once shared blocks of glacier ice with pilgrims, but the practice was stopped when locals noticed the rapid retreat in recent years.

Small glaciers at low or medium altitudes will be the first to disappear. UNESCO said ice-loss rates in small glaciered areas “more than doubled from the early 2000s to the late 2010s.”

This matches observations from researchers who have studied the retreat of glaciers. Matthias Huss, a European glaciologist, said scientists had seen “very strong melting in the last two decades” in Switzerland.

At the same time, there are fewer and fewer places cold enough for glaciers to actually grow. “Nowadays, the limit where glaciers can still form new ice is at about 3,000 meters [about 9,840 feet],” he said, explaining that in recent decades that altitude has risen several hundred meters.