Ten of the world’s most highly protected forests have become net sources of carbon, as they are degraded by human activity and climate change.

The alarming insight is from a study of  planet-warming gases emitted from and absorbed by forests in Unesco World Heritage sites.

It revealed 10  protected forests had emitted more carbon than they locked away over the past 20 years.

World heritage forests span an area twice the size of Germany.

The same research also revealed the network of 257 World Heritage forests around the world collectively removed 190 million tonnes of carbon from the atmosphere every year.

“That is nearly half of the UK’s annual carbon emissions from fossil fuels,” said Dr Tales Carvalho Resende, from the United Nations Educational, Scientific and Cultural Organization (Unesco), who co-authored the report. 

“We now have the most detailed picture to date of the vital role that [these] forests play in mitigating climate change.” 

Combining satellite-derived data with monitoring information at the site level, researchers estimated the carbon absorbed and emitted by  World Heritage forests between 2001 and 2020.

But as well as calculating the billions of tonnes of carbon absorbed by all that “biomass” of trees and vegetation, the research revealed how much pressure some of these sites were under.