Air quality on the west coast of the US has deteriorated to become the worst in the world as wildfires choke major cities, forcing residents to stay indoors for days on end.
On Tuesday Portland, Oregon and Seattle, Washington had the dirtiest air in the world, ahead of Bishkek, Kyrgyzstan and Delhi, India.
Pollution from fire smoke has meant air is dangerously polluted as far south as Los Angeles and as far north as Vancouver, Canada, but Portland and other Oregonian cities have been particularly badly affected.
Data from US agency the EPA showed that much of the state was experiencing an Air Quality Index (AQI) of over 400 - classed as "hazardous".
Residents were warned to stay indoors and use air purifiers if possible, with elderly people, pregnant women, children and those with underlying conditions such as asthma at particular risk of suffering complications including heart and lung problems.
Dr Jennifer Vines, the lead health officer for the Portland city area, said the region was seeing a "sharp increase" in hospital visits for respiratory issues.
"Many of those visits seem to be related to asthma and people directly relating their visit to the smoke," she told local broadcaster PBS.
As well as trouble breathing, headaches and coughs, small particulate matter from fire smoke entering the lungs and bloodstream is thought to lead to an elevated risk of heart and lung disease and other long-term health problems.
Last week parts of the state experienced figures off the AQI charts, with readings as high as 700 recorded.
At least 35 people have died in the fires which have spread across California, Oregon and Washington, with more than a million acres burned in Oregon alone, double the average for previous years.
Fire spread has been exacerbated by record high temperatures, dry conditions and unusual weather events, including a mostly dry lightning storm in California last month.
Globally, fires also burned in Brazil and Portugal. The Amazon burned for the second consecutive year, with mining and agriculture also driving fires in Colombia, Peru and Venezuela.
Mike Barrett, executive director of science and conservation at the WWF, said that the atmosphere above the Amazon was drying out because of particulate matter being released by burning, raising the risk of further fires.
"The best scientific estimates are that if we lose in the order of another five per cent of the forest, the effect is that it actually then ceases to be a functional rainforest. It will convert to a dry savanna.
"The reason for that is because a rainforest generates a lot of its own moisture. As you take more and more trees, more and more vegetation out of the system, it's unable to do that. So you have this over-drying," he said.
On Tuesday the United Nations said that the world was due to run out of names for the Atlantic hurricanes and tropical storms that typically strike between June and November, for only the second time in history.
The storms are named using the English alphabet, with male and female names alternating, and excluding the letters Q, U, X, Y and Z.
Just one name - Wilfred - remains unused, leading subsequent storms to be named using the Greek alphabet instead.
"The 2020 Atlantic hurricane season is so active that it is expected to exhaust the regular list of storm names," said Clare Nullis, spokeswoman for the UN's Geneva-based World Meteorological Organization (WMO).