A cloud of smoke that is bigger than the European Union is covering large parts of Siberia.
Wildfires in Russia continue to reach for a third month across the normally frozen region.
The UN's World Meteorological Organization (WMO) said the wildfire smoke covers more than 5 million square km (more than 1.2 billion acres or 500 million hectares), a size larger than the European Union, which is about 4.5 million square km or 1.1 billion acres or 450 million hectares.
A number of large fires in Russia, Greenland, Alaska and Canada have discharged 50 megatonnes of CO2 in June and 79 megatonnes in July, The Guardian reported.
A total of 25 megatonnes has been discharged so far in August.
Russian president Vladimir Putin called in the army last month to combat the fires, while four regions of Siberia declared a state of emergency.
It is thought that the blazes have destroyed 4.3m hectares in Siberia alone.
Greenpeace Russia wildland fire expert Anton Beneslavskiy said: “These fires should have been put out at the very beginning, but were ignored due to weak policies.
“Now it has grown into a climate catastrophe that can not be stopped by human means.
“Russia should increase efforts in forest protection and provide sufficient funding for firefighting and fire prevention.
“The problem of wildfires should be addressed at the international level in the global climate agreements to keep global warming below 1.5°C.”
Greenpeace warned the situation will “remain catastrophic” in the next two weeks because of weather conditions.
Smoke has blown away from major Siberian cities but continues to surround settlements in remote forest areas, it said.