The city of Chicago has become a zone of smoke due to wildfires that have spread across Canada

In Chicago, Illinois, where only the skyline was obscured by fog on Tuesday, the mayor called on children, the elderly, pregnant women and people with heart and lung problems to avoid strenuous activity and spend some time outside. “Cities across North America have experienced unhealthy air quality this summer due to wildfire smoke, affecting more than 20 million people today in New York City, Washington DC, Montreal and Chicago,” Mayor Brandon Johnson wrote on Facebook on Tuesday. The “disturbing episode” highlights the damaging effects the climate crisis is having on city dwellers and people around the world.

Fires have been raging across Canada for weeks. In early June, smog blanketed parts of the US East Coast, causing the worst air quality in the New York metropolitan area in decades. Even in Portugal, a cloud of smoke is currently darkening the sky – according to the Portuguese Institute for the Ocean and Atmosphere (IPMA), it also comes from a fire in Canada.