Russia is now on track to have a record year for wildfires as hundreds of blazes torch huge swaths of Siberia for the third month in a row after an unusually hot and dry summer left forests primed to burn.

The fires, likely ignited by lightning and strengthened by strong winds, have already burned more than 21,000 square miles, an area larger than the state of Maryland. Though Siberia is sparsely populated — it’s home to just a quarter of Russia’s population — these blazes are alarmingly close to cities and are impacting people’s health.

But the impact of these wildfires is already spreading far beyond Russia’s borders. The smoke from the blazes now shrouds an area larger than the European Union and is moving into the Arctic, according to the World Meteorological Organization. Parts of the Arctic including Greenland have suffered wildfires of their own this summer. The region is already experiencing its worst wildfire season on record.

Where is the Siberian wildfire smoke spreading to?@ECMWF predicts that it will cross the Arctic Ocean and reach northern #Greenland over 13/14 August.



READ MORE▶️https://t.co/HJ2OAfPkE7pic.twitter.com/YlXwrlUX8h — WMO | OMM (@WMO) August 13, 2019

Residents of Novosibirsk, Russia’s third-largest city, located in southern Siberia, have suffered from the poor air quality, which have led to hacking coughs, stinging eyes, and hospital visits. The city of Ulan-Ude was also clouded by smoke. Dirty air stemming from blazes is often the deadliest health effect of wildfires, and the impacts can linger for years.

And the smoke is now crossing oceans. NOAA satellites have observed that the massive plumes have moved east and into North America in July.

Though wildfires are a regular event in Siberian forests, the scale of the current infernos is unusual. For some environmentalists, the biggest concern is that the soot from the fires can deposit on Arctic ice and speed up its melt rate. That in turn can cause major disruption to local ecosystems. And if that ice is on land, it can run into the ocean and contribute to sea level rise.

“The catastrophe in Siberia is not a catastrophe in Russia, it is a global ecological catastrophe,” Anton Beneslavsky, a Greenpeace Russia fire expert and volunteer firefighter, told Vice News.

The Russian government declared an emergency and mobilized the military to contain the fires. Airplanes and helicopters are working to constrain the flames but can do little to limit the smoke. Many of the fires are in remote areas that are difficult to reach.

The President instructed the Defence Ministry to assist in putting out the fires in Siberia https://t.co/e3HdNOseFb — President of Russia (@KremlinRussia_E) July 31, 2019

Last month, President Trump spoke with Russian President Vladimir Putin to offer US assistance in fighting the fires.

Fires are not unusual in Siberian forests, but the concern about this year’s blazes is their scale and their proximity to population centers. Siberia also saw massive fires last year, the year before, and the year before that. The most recent fires were preceded by temperatures upward of 14 degrees Fahrenheit warmer than the long-term average for the area. That fits within the pattern of what scientists expect as the global climate changes. As average temperatures rise, heat waves are becoming longer, more frequent, and more intense.