Last summer's forest fires in Yukon and Alaska sent carbon monoxide pollution around the world, scientists say.

Researchers looking at the effects of the fires on the atmosphere say the fires raised ozone levels around the northern hemisphere, and produced a record amount of carbon monoxide.

Last year's forest fires in Yukon fires dumped 30 billion kilograms of carbon monoxide into the atmosphere.

The Yukon wildfires in June to August 2004 added about 30 billion kilograms of carbon monoxide into the atmosphere – about as much as was released by human-related activities in the continental U.S. during the same period, the scientists said.

Six per cent of Yukon's forests were burned and the Alaskan government spend $100 million to fight fires in the state.

Researchers at the National Center for Atmospheric Research in Boulder, Colo., used a combination of computer models, satellite readings, ground sampling and numerical techniques to distinguish the carbon monoxide coming from wildfires from other sources.

Ground-level concentrations of ozone increased by 25 per cent or more in parts of the northern continental U.S., and as much as 10 per cent as far away as Europe, the team reported in this month's issue of the journal Geophysical Research Letters.

"Globally, we are all connected," said lead researcher Gabriele Pfister of the centre. "An event in one area can affect air pollution in another area far, far away from us."

The fire released about 30 billion kilograms of CO from June to August of last year, the researchers reported in this month's issue of the journal Geophysical Research Letters.

Fires in the north were particularly intense in the summer of 2004, largely because of unusually warm and dry weather.

Carbon monoxide is a toxic gas that can harm human health even at low levels. It's commonly produced by motor vehicles and industrial facilities. Ground-level ozone is produced from reactions with pollutants, including C0.

"These fires were hopefully a record event and let's hope these fires don't become the rule," said Pfister.

Pfister said the team is still processing data from observing stations as far away as the Azores in the middle of the Atlantic Ocean.

They are also planning to apply the modelling technique to carbon monoxide emissions in South America.