Wildfires currently burning across Russia have doubled in size over the past week, the state-run TASS news agency reported Monday, citing a source in the Federal Forestry Agency.

“Over the week, the total area of ​​forest fires has more than doubled,” TASS quoted its source as saying. “The most difficult situation is developing in Siberia and the Far East.”

According to Russia’s agency for aerial forest fire management Aviales, a total of 148 forest fires were burning across 67,913 hectares of land as of midnight Monday. At the same time last week, 155 fires were burning across 32,984 hectares of land.

Environmentalists have warned that this year’s blazes could become the worst in Russia’s history and exacerbate global climate change. Siberia’s wildfires have already burned an area larger than the size of Greece, Greenpeace Russia said.

The Forestry Agency says it will not extinguish 91% of the fires because they are located in “control zones.” Forests fall into control zones when the fires have no effect on local populations and when the cost of extinguishing them is greater than the residual damage of the fires.