Bowing
Antarctic tourism is increasing each year, the vast majority by ship. Though this allows people to enjoy the continent’s stunning landscapes, a new study reveals how this rise combined with forest fires in the Southern Hemisphere causes seasonal changes in black carbon levels.
“Even a tiny bit of black carbon in the bright snow surface will reduce the albedo, cause the snowpack to warm, and eventually cause it to melt.”
Refractory black carbon (rBC) is a type of black carbon that comes from burning fossil fuels and biomass. It plays a significant role in climate change because it not only warms the atmosphere but also contributes to the melting of ice. When rBC from ship emissions or wildfire smoke lands on snow, it darkens the surface and reduces the albedo, or the snow’s ability to reflect solar radiation. As Joe McConnell, a climate scientist at the Desert Research Institute involved in the study, explained, “Black carbon is a very good absorber of energy. Even a tiny bit of black carbon in the bright snow surface will reduce the albedo, cause the snowpack to warm, and eventually cause it to melt.”
Previous studies based on samples from near research facilities and popular tourist sites have revealed concentrations of rBC ranging from 1 to 8 nanograms of rBC per gram of snow—much higher than the typical 0.1–0.2 nanogram per gram observed in the past. Others have found seasonal patterns, with peaks during biomass-burning seasons. However, all of these studies have examined local and distant sources of rBC separately. According to the authors, this study is the first to attempt to look comprehensively at rBC sources in the northern Antarctic Peninsula.
Researchers conducted high-resolution measurements of rBC levels in a 20-meter ice core from the Detroit Plateau near the northern tip of the Antarctic Peninsula. After dating layers of the core, they zeroed in on rBC data from 2003 to 2008. Rates of deforestation and fires were particularly high during this period, and the summer of 2007–2008 marked the first tourism boom in Antarctica.
To assess the effects of both distant and local rBC emissions, the researchers also analyzed atmospheric rBC data from satellite measurements and models, such as the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as information on burned areas and tourism activities.
rBC Seasonality
Raul Cordero, a climate scientist at the University of Groningen in the Netherlands, was not involved in this study, but he coauthored a 2022 paper on how human presence in Antarctica affects black carbon levels.
“There’s something this paper has that our paper doesn’t,” he said. “We focused on local sources of black carbon emissions, while they suggest—and we agree—that some pollution comes from distant fires.”
The study reported that annual rBC concentrations ranged from 0.01 to 3.73 nanograms per gram and were highest during the spring and summer.
“Touristic activities occur when the snow and ice are most sensitive to black carbon.”
During Antarctic summer (December–February), tourist ships visited Antarctica, raising black carbon levels. Warmer temperatures and increased sunlight allowed this black carbon to absorb more heat. “Touristic activities occur when the snow and ice are most sensitive to black carbon,” said Newton Magalhães, a geoprocessing analyst at Rio de Janeiro State University in Brazil and first author of the new study. Therefore, summer peak levels of rBC are largely attributed to tourism.
In the fall (March–May), the Southern Hemisphere saw the lowest burned area and minimal tourism, leading to the lowest rBC emissions. During winter (June–August), tourist activities and research operations decreased, but biomass burning peaked in southern Africa and South America, contributing significantly to rBC emissions.
In spring (September–November), when tourism was low (or not present at all from 2003 to 2005), rBC concentrations remained high, suggesting contributions from distant sources. For instance, during the 2007 Amazon fire season, rBC levels in the Detroit Plateau core reached 3.7 nanograms per gram.
Magalhães noted that though both local and long-range sources contribute to rBC, “quantifying their [relative] contributions is still a challenge.” In winter, rBC peaks can typically be attributed to biomass burning, but it becomes difficult to pinpoint a source when tourism and burning co-occur. He suggested that future research could use carbon-14 to quantify the relative contributions from fossil fuels and biomass fuels. Fossil fuels contain little to no carbon-14 because of their age, whereas biomass fuels contain measurable carbon-14 levels.
Magalhães and McConnell suggest that in the future, tourist ships could reduce rBC emissions by using higher-quality fuel. “Black carbon is a result of incomplete combustion, so if you get complete combustion, you get very little or no black carbon. Higher-quality fuel means more efficient combustion,” said McConnell.
—Larissa G. Capella (@CapellaLarissa), Science Writer
