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The billowing black smoke that has engulfed the United States' Pacific Northwest in recent years has caused atmospheric carbon monoxide levels to rise, scientists at the National Center for Atmospheric Research have found, explaining that the contaminants were offsetting recent reductions in emissions.

As the American West faces increasing threats from large fires fueled by a warming and drier climate, researchers have documented the impact of smoke on public health and safety. 

See more: The Cost of Climate Change

Scientists are increasingly discovering that the fires may be part of a feedback loop that could accelerate the change in conditions and that the health impacts officials have long warned would worsen as a result of the climate crisis may, in fact, already be here. 

Carbon monoxide concentrations fell by half a percentage point per year globally over the 16-year study period. 

However, the scientists discovered that August was an outlier across North America. Carbon monoxide levels in the atmosphere have a seasonal cycle, with ebbs and flows caused by a photochemical process. 

Before 2011, the regions followed this pattern, with pollutant levels peaking in the spring and declining in the late summer. 

A new trend began to emerge in a more recent period studied by the researchers - from 2012 to 2018.

In August, when CO was expected to be at its lowest, there were spikes instead. The scientists discovered that this not only affected atmospheric carbon monoxide but was also discovered closer to the Earth's surface. 

The deviation from the global trend was greatest in the Pacific north-west, where wildfire risks were high during that month, but the effect lingered in data collected across the country. 

Four different global fire emission inventories consistently showed that carbon monoxide fire emissions peaked in the Pacific north-west in August, supporting the study's findings. 

Carbon monoxide levels in the region were not increasing during the study period, according to data from two other inventories that catalog emissions from human activity, allowing the researchers to rule out other causes of the August surge and its spread.

The toxic output of fires is hazardous, contributing to an estimated loss of more than 15,000 lives in the United States each year. 

According to some scientists, that figure will more than double by the end of the century.

According to a separate study published last year, smoke from Western fires has been linked to up to 5,900 asthma-related emergency department visits per year.

Almost three-quarters of these visits and hospitalizations related to smoke inhalation occurred outside of the western US.

While some questions about the link between ignitions and the climate crisis remain, it is clear that rising temperatures are hastening the desiccation of landscapes and priming them to burn. 

Land management, including the use of prescribed fire – which does not burn with the same intensity or smoke – is critical in mitigating the risk of disasters. People continue to be the primary cause of fires. However, as the West warms, larger fires are expected to follow. According to the findings of this study, this could have a longer-term impact.