Some of the world’s most protected forests are emitting more carbon than they absorb, owing to factors such as logging and wildfires, according to a new report released on Wednesday, with scientists concerned that protected areas are contributing to climate change.

According to the report, at least ten World Heritage sites, including Yosemite National Park in the United States, have been net carbon emitters over the last two decades.

“The fact that even some of the most iconic and well-protected forests, such as those found in World Heritage sites, can contribute to climate change is alarming and demonstrates the severity of this climate emergency,” Tales Carvalho Resende, report co-author and project officer for the United Nations Educational, Scientific and Cultural Organization (UNESCO), said in a statement.

Forests are important for mitigating climate change because of their ability to act as carbon sinks. Trees and other plants remove greenhouse gases from the atmosphere by absorbing carbon dioxide and emitting oxygen.

According to the study, which covered the years 2001 to 2020, all 257 forests act as a net carbon sink. Nonetheless, human activities such as logging and intense climate-related events such as wildfires are impeding their ability to capture and store more carbon than they emit, which experts say is a serious concern.

In addition to the United States, forests found to be net carbon emitters were discovered in Indonesia, Australia, and Russia, among other countries. UNESCO investigators and researchers from advocacy groups the World Resources Institute (WRI) and the International Union for Conservation of Nature (IUCN) combined satellite data with on-site monitoring and discovered that over a 20-year period, the heritage sites net absorbed 190 million tons of CO2.

According to the report, forests have stored 13 billion tons of carbon over centuries, which is equivalent to Kuwait’s proven oil reserves.

The findings were based on data published in January by the journal Nature Climate Change, which mapped global greenhouse gas emissions and absorption by forests.

The researchers used this information, as well as on-the-ground monitoring of the heritage sites, to better understand what is threatening forests, such as logging, agricultural incursions, droughts, and changing temperatures.

“I would expect all of them to be removing carbon from the atmosphere rather than being carbon sources,” Carlos Sanquetta, a forestry engineering professor at Brazil’s Federal University of Parana, told reporters. “Instead of contributing to carbon sequestration, they contribute to carbon emissions.”

He believes that, while the report produced important findings, it could have presented its methodology in greater depth. While only ten of the UNESCO-protected forests were found to be carbon emitters, other sites showed clear upward trajectories in emissions, according to the report.

“This is yet another clear indication that even forests we previously assumed were safe are now under increasing threat,” David Kaimowitz, one of the UN Food and Agriculture Organization’s forest directors, told reporters.

According to him, the report does not place enough emphasis on supporting indigenous and local communities, as well as activists who oppose forest destruction. He also questioned whether the report accurately represented all forests. “Readers should … not assume that the specific numbers presented here apply to forests everywhere,” he said.