Long-dead birds gathering dust in museums are helping scientists to better understand climate change.
By examining soot on the feathers of bird specimens collected by museums over the last 150 years, scientists are getting a rare glimpse into the history of U.S. carbon emissions. Their findings, published Monday in Proceedings of the National Academy of Sciences, could also aid in predictions of future climate change.
The researchers—biologist Shane DuBay and photography expert Carl Fuldner, both of the University of Chicago—examined more than 1,300 birds collected between 1880 and 2015 from Pennsylvania, Ohio, Indiana, Michigan, Illinois and Wisconsin, the region historically most heavily involved in manufacturing and coal burning.
Those specimens helped them construct a record of "black carbon" concentrations in the United States.
Black carbon is a type of particulate matter produced by the burning of fossil fuels. It's long been known as a major source of air pollution and a threat to public health, but in recent years, it's also been identified as a potent contributor to climate change. In fact, two analyses—one in 2008 and another in 2013—have suggested that black carbon is the second-greatest human cause behind the planet's warming, right behind carbon dioxide.
The reason behind its powerful influence is apparent in the name—the dark color of the particles allows them to absorb more heat than other pollutants. As a result, "historical emission inventories of black carbon [are] an essential tool for assessing past climate sensitivity and modeling future climate scenarios," the researchers write.
The problem is that there are no direct records of black carbon emissions throughout most of society's industrial history. Scientists have previously relied on two methods to estimate historical emissions: models and data from Arctic ice core samples, which contain information on the air quality up to hundreds and even thousands of years in the past.
But while their findings tend to be similar, the two methods don't always produce exactly the same estimates. And so scientists are still questioning just how much black carbon has been going into the atmosphere, according to Veerabhadran Ramanathan of the University of California, San Diego, one of the researchers who first identified the climate-forcing significance of black carbon back in 2008.
"This paper presents an ingenious new way of reducing that uncertainty," Ramanathan, who was not involved with the new study, said by email.
Researchers used a special technique that measures the amount of light reflected off the birds' feathers. The darker the feathers, the more soot they contained.
The researchers also relied on bird species that molt, or shed their feathers, every year. Each molt would have cleared away all of the previous year's accumulation of soot, meaning that each of the specimens presented a snapshot of only the black carbon concentrations present during the year they died and were collected. As a result, the researchers were able to construct a record of black carbon concentrations over the course of nearly 150 years.
The results indicate that black carbon concentrations may have been higher in the past than model estimates have suggested, particularly between 1880 and 1910. This means that black carbon may have had a greater impact on the Earth's changing climate in the past than scientists realize, the researchers suggest.
And the birds may yet help unlock more secrets.
As the authors note, the size and shape of black carbon particles help determine the heat they absorb and their impact on the climate. "Thus knowing the historical size distribution of black carbon particles is critical for evaluating their climate impacts and building a usable emission inventory," they write.
In the future, they suggest, scientists could further analyze the bird specimens' carbon deposits to construct a record of their physical properties from any given time and location, thereby creating an even more detailed record of the emissions that have shaped our climate up to this point.
In the meantime, the findings so far don't necessarily drastically change scientists' understanding of historical black carbon emissions, but they refine it in ways that could help make model predictions more accurate in the future. And as the researchers point out, they also demonstrate that unconventional sources of information—even dead, stuffed birds, long hidden away in museums—can produce surprising insights into both the past and the future.
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.