- The Amazon rainforest was historically too wet to burn on a large scale, but that has changed as climate change and deforestation have made the biome hotter and dryer.
- A new study finds that fire impacts (specifically in 2007 and 2010, bad fire years), are resulting in black carbon deposits that darken Andes mountain glacial snows. Absorption rather than reflection of solar radiation makes for increased glacial melt.
- The amount of melting depends on how much Amazon fire soot reaches the glacial surface, which is dependent on the amount of soot produced and also on atmospheric conditions, such as wind direction. This black carbon initiated melting isn’t accounted for in current climate models, meaning that the models may be underestimating future melt.
- Black carbon initiated melting over the short term is expected to result in increased water outflows from mountain glaciers, possibly causing flooding. But once the glaciers melt away, severe water shortages could occur in the Andes, though there is no timeframe for such an outcome.
Fires in the Amazon may be melting Andean mountain glaciers at an increased rate, according to a study published in Scientific Reports. Smoke plumes billow from Amazon forest fires and travel with the wind, carrying aerosols such as black carbon to settle upon the surfaces of mountain glaciers, darkening snow.
As a result, the snow’s albedo — the amount of light and radiation reflected from the surface — is reduced. With less sunlight reflected, the glacier warms and melts more rapidly.
“What we found in our study was that for the tropical Andean glaciers, the main source of black carbon is the Amazon biomass burning. And that the black carbon content in snow due to Amazon fires is sufficient to cause melting,” study lead author Dr. Newton de Magalhães Neto of Brazil’s Rio de Janeiro State University, told Mongabay.
The phenomenon may be relatively new, as the Amazon rainforest historically was too wet to burn significantly; climate change coupled with deforestation has caused it to grow increasingly dryer over recent years.
The research team used data from past fire events, precipitation, glacial melting and the movement of smoke plumes from the southwestern Amazon to model effects on glacial melting, specifically for the Bolivian Zongo Glacier. The research focused on black carbon deposition in 2007 and 2010, years when fires surpassed the devastating levels seen in 2019.
According to the researchers’ model, both black carbon and dust in low concentrations (10 parts per million) on the surface of the snow can increase annual melting on the glacier by 3-4% separately, or by 6-8% in combination. Higher levels of dust (100ppm) can increase annual glacial melting by 12-14% when combined with black carbon.
“For us that was not a big surprise. We already knew that in Greenland, surface melting occurs not only due to greenhouse gases warming but also due to surface deposition of black carbon,” said de Magalhães Neto. “Greenland receives large amounts of black carbon of fossil fuel origin due to North American and European industrialization, boreal forest burning from Canada, and from coal use in Russia, and black carbon plays a key role in the surface melting process.”
To make the same connection in the tropics, however, the researchers had to prove that smoke plumes from the southwestern Amazon could reach the altitude of Andean tropical glaciers. The team did this by using CALIPSO (a satellite that utilizes lidar, infrared and imaging analyses to evaluate clouds). CALIPSO could verify that a plume of smoke containing the same aerosol composition was appearing over both the Amazon basin and Andean mountains.
CALIPSO, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, combines an active Lidar instrument with passive infrared and visible imagers to probe the vertical structure and properties of thin clouds and aerosols. Video courtesy of NASA Langley Research Center.
Deforestation is on the rise in the Amazon, and the rainforest drying trend is ongoing, which raises the potential for increased fires in the future. However, the quantity of fire emissions isn’t the only contributor to the darkening of Andes glaciers. How easily black carbon can travel from the Amazon to the mountains, according to de Magalhães Neto, is also a consideration. Changes in the atmosphere could mean more efficient transport of dust and carbon to glacial surfaces.
“It is difficult to predict what this year’s  fires mean for melting without modeling the process for this year and measuring black carbon on the glaciers,” said de Magalhães Neto. The most important [concept] is to have in mind that such an impact does exist.”
A survey of other tropical Andean glaciers found that nearly half of all glacial area has vanished since 1975, with over 80% disappearing in areas below 5,000 meters (16,404 feet). Current models predicting the response of Andean glaciers to climate change do not include the contributions of black carbon and dust to melting — meaning that their melt rate could be higher than expected.
“Know that the most important cause of glaciers melting in the Andes is climate change (mainly atmospheric warming due to greenhouse gases). Amazonian fires act as an extra forcing that aggravates the situation,” said de Magalhães Neto. “A joint policy of reducing greenhouse gas emissions and stopping deforestation and fires would be the most effective way to mitigate the ongoing melting of glaciers.” However, implementing such mitigation efforts now while Brazil’s President Jair Bolsonaro is in office, pushing his anti-environmental policies, seems unlikely.
Communities and ecosystems downstream from glaciers rely on glacial melt as a source of freshwater, especially during dry seasons and times of drought. Increased glacial melting may disrupt the hydrological balance and could have disastrous implications for the freshwater resources in regions already faced with water insecurity in the Andes Amazon.
“First, an initial increase in glacier water discharge is expected as a result of the increased melting. However, the melting of the glaciers will reach a point where the discharge will begin to decrease,” explained de Magalhães Neto. This “will result in a water deficit to the ecosystem, which can cause future declines of agriculture, potable water and power generation for people that live in the arid regions of the western Andes and result in a water crisis.” How quickly or soon such a crisis might occur isn’t yet known.
Banner image caption: Forest fires burn out of control in the municipality of Colniza, Mato Grosso state, Brazil, August 2019. Image by Victor Moriyama / Greenpeace.
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