Canada'sworst wildfire season on recordtarnished the country'sair qualityand had similar effects on pollution inparts of the United States, according to a new report. University of Chicago researchers on Thursday released their annualAir Quality Life Index, a situational update on air pollution and how it impacts life expectancy. The AQLI report said particulate pollution "remained the greatest external threat to human life expectancy," comparing the impact to smoking. Researchers from the university's Energy Policy Institute analyzed pollution data collected throughout 2023 and compared it with previous years. Michael Greenstone, a professor at the University of Chicago who created the AQLI, told CBS News his team focused on airborne particulate matter — small particles that are able to invade and wreak havoc on the body more easily than larger ones. The data is taken from satellite readings that refresh each year and can take time to process, which is why the latest figures date back a couple of years, Greenstone said. While global pollution only rose slightly between 2022 and 2023, the report's authors found that updated levels remained almost five times higher thanthe limit recommendedby the World Health Organization to protect public safety. Local changes in air quality varied from one country to the next. The differences were particularly stark in the U.S. and Canada, where airborne particulate concentrationsincreased more than anywhere else. "Evidence of a link between climate change, wildfire smoke, and rising particulate pollution has been increasing over the past two decades," the authors wrote in their report, citing a recent study that found human-caused climate change "increased the likelihood of autumn wind-driven extreme wildfire events, especially in the Western U.S." Extreme wildfires, particularly forest fires, have become larger, more common and more intense since the beginning of this century,according to NASA. The Canadian wildfires caused particulate concentrations in Canada to soar to levels not seen since 1998, according to the AQLI. In the U.S., the wildfires drove up pollution to levels not seen since 2011 — a 20% uptick from the levels recorded in 2022. Wisconsin, Illinois, Ohio, Pennsylvania, Oklahoma and Mississippi were markedly affected, with pockets of those states replacing 20 counties in California as the most polluted nationwide. Out of 3,137 American counties, the number of locations with pollution levels above thenational U.S. standardrose to 308 in 2023, up from just 12 in 2022, according to the report. Forty-eight of the counties were in Ohio, 41 were in Wisconsin, 31 were in Pennsylvania, 26 were in Indiana and 19 were in Illinois, with the remaining 143 spread across the rest of the country. In Canada, the researchers said that 50% of residents in 2023 breathed air that contained particulates in amounts exceeding theirnational air quality standard. That was a sharp turnaround in the country's progress in pursuit of cleaner air, which had resulted in particulate levels falling below the national standard in previous years, said the report's authors, noting that particulate levels in Canada's most polluted regions were roughly equal to those of Bolivia and Honduras, two countries that face are known to face challenges addressing air quality and pollution. The Canadian provinces of Alberta, British Columbia and the Northwest Territories experienced the country's worst pollution, according to the report. That reflected some of the locations ofdestructive wildfiresthat collectivelyburned more than 71,000 acres of landfrom the East to West Coasts.Smoke from those blazespermeated the atmosphere over Canada and the U.S., creating hazy, and at times, orange, skies while health posing threats to people with certain conditions. Wildfiresscorching Canada this summerhave again given rise to serious air quality concerns, for Canadians and Americans alike. "It's correct to think of this air pollution from the wildfires as, kind of, the ghost of fossil fuels past," Greenstone told CBS News. He said that the U.S. hasover the last half-centurymade "enormous progress" toward blocking particulates generated through the burning of fossil fuels, like oil and gas, from entering the air. The AQLI credited the implementation of theClean Air Actfor reducing particulate concentrations by over 60% since 1970, which it says added 1.4 years to the life expectancy of American residents. But the devices used to block particulates do not prevent carbon dioxide from infiltrating the atmosphere, driving up temperatures and increasing both the incidence and the severity of wildfires, Greenstone added. When trees burn in a fire, more particulates are produced and released again. "The point we're trying to make is that CO2 that's released when we use fossil fuels, both historically and today, it stays up in the atmosphere for centuries, and it raises temperatures, and it will continue to for centuries," Greenstone said. "What we're seeing is an important consequence of that, which is, it's going to increase the incidence of wildfires going forward. And those wildfires are causing us to breathe air that is going to cause us to lead shorter and sicker lives." 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