Wildfires are raging across over 15,000 square miles of Siberia, an area larger than the size of Massachusetts, and are causing what one environmental expert calls a “global ecological catastrophe.”

Some 46 thousand square miles have already been destroyed, and with the fires now threatening towns and cities, and large clouds of black smoke engulfing Russia's third-biggest city, Novosibirsk, the Kremlin has come under increasing pressure from the public and from environmentalists to act to tackle the fires.

But experts say that these moves will do little to bring the fires under control.

"Unfortunately, with the current size of four million hectares [15,400 square miles] and firefighting efforts limited to 100,000 hectares [386 square miles], additional army forces, which are mostly aircraft, will not make a big difference, especially as the military are not experts in fighting forest fires,” Anton Beneslavsky, Greenpeace Russia fire expert and volunteer firefighter, told VICE News.

Large wildfires are an annual occurrence in sparsely populated northern Russia, but this year strong winds and dry weather conditions have seen the fires threaten populated areas.

Putin ordered 10 planes and 10 helicopters with firefighting equipment to help prevent the fires from reaching towns and cities, but smoke from the blaze has already done damage in populated areas.

"The smoke is horrible," Raisa Brovkina, a pensioner in Novosibirsk, told state television after being hospitalized for smoke inhalation. "I am choking and dizzy.”

Russia typically doesn’t try and fight the fires and has created control zones inside which blazes are allowed to run their course. The Kremlin says that the cost of tackling these fires is much greater than the damage they cause.

But for weeks, environmental activists have been warning of the size and scale of this year’s blaze, and now some are criticizing the government for not acting sooner this year.

Scientists and rights groups have launched petitions in recent days to try and persuade the Kremlin to do more.

A petition by an ecologist from the Siberian city of Tomsk has garnered over 860,000 signatures, while one by the Russian charter of Greenpeace has been signed by 330,000 people as of Thursday morning.

The petitions have pressured the government to declare states of emergency in five regions.

On Wednesday evening, the Kremlin announced that Putin and Trump had spoken about the wildfires by phone.

“The U.S. president offered Russia cooperation in fighting forest fires in Siberia,” the Kremlin statement said. “President Putin expressed his sincere gratitude for such an attentive attitude and for the offer of help and support.”

The White House confirmed the call, saying Trump “expressed concern over the vast wildfires afflicting Siberia” adding that they also discussed “trade between the two countries.”

However, it’s unclear what the U.S. can do to help stop the fires from burning out of control.

As well as the damage caused to the Siberian landscape and the danger posed to the public's health in Russia, the fires have a global impact, thanks to the increased CO2 and black carbon emissions. The fires also speed up the rate at which ice melts in the Arctic.

“The catastrophe in Siberia is not a catastrophe in Russia, it is a global ecological catastrophe,” Beneslavsky said.