May 27, 2020

Fires in the Amazon melt the Andean glaciers | Science

The fires that burn the Amazon rainforest and savanna have another effect far from there: thaw the Andean glaciers. It is the conclusion reached by a study that shows how the soot from burning travels through the air to the mountains and, when deposited on the ice, increases the solar radiation it traps, accelerating its fusion. The work has focused on a small glacier, but its results could be reproduced in the hundreds of glaciers of the Andes, already punished by climate change.

On August 23, 2010 there were 148,946 fires in the Amazon region. That southern summer was the worst of the century in terms of fire, even greater than this year's. The smoke, populated with soot or black carbon from combustion, clouded the Andes, as the archive shows NASA satellite images. Days after the fires surge of that year there was a peak of discharge of water from several glaciers. Now, Brazilian and French researchers have joined the points.

In a paper published in the scientific journal Scientific Reports, the researchers collected existing data on fires so far this century in the Amazon region. The vast majority occur between August and October, when the transition between the dry and wet seasons occurs. In those months, the lack of rainfall prevents them from dragging soot from burning. It is estimated that the burnt vegetation cover in South America generates about 800,000 tons of soot per year.

On August 23, 2010 there were almost 150,000 fires in the Amazon region

To complicate matters, in the months of the fire season the prevailing winds in the region, until then from the west, roll east / northeast, towards the Andean peaks. To find out where the smoke column is headed, scientists also analyzed more than 2,000 smoke paths in those months since 2000 and 2016. With these data they were able to create a model of black carbon particle deposition on ice and how these impurities reduced its albedo effect, that is, its ability to reflect solar radiation.

The scientists applied their model to the Zongo, a small glacier of the Cordillera Real, in the Bolivian portion of the Andes. There, French glaciologists (some co-authors of the research) have a base from which the data on soot particles accumulated in the ice and the annual discharge in the form of water lost by the glacier have emerged. In 2010, the study indicates that for every square meter of ice there was 1.17 milligrams of black carbon in its most superficial layer. In concentration, in September of that same year there were 73.4 parts of soot per billion of matter (ppmm). The figure fell to 29.2 ppb in October.

With these figures, the study authors estimate that only soot could reduce the albedo effect by up to 7.2%. "That means that due to the deposition of black carbon, snow absorbs up to 7% of the incident radiation," says a researcher at the State University of Rio de Janeiro and lead author of the study, Newton de Magalhães Neto. If pollution from other sources (dust, urban pollution, etc.) is added, the reduction percentage could reach up to 20.2%. The consequence is a greater thaw: "We estimate that between 3% and 4% of the melting of the glacier is due to fires," adds Neto.

Although the result can only be applied to this glacier, the authors of the work believe that the fires would also be aggravating the melting of more Andean glaciers. In fact, previous studies in a hundred glaciers of the Cordillera Blanca, in the Peruvian Andes, they found a concentration of black carbon of up to 80 ppmm, even higher than that found in the Zongo.

"The snow can reflect up to 85% of the solar radiation while the albedo effect of the ice is less, from 30% to 40% of the radiation," recalls the physicist at the Polytechnic University of Madrid and president of the International Glaciological Society Francisco Navarro Among the elements that can reduce albedo the most are pollution from human activities or dust from deserts. "But the maximum reduction is produced by volcanic eruptions, especially if the volcano has an associated glacier. So, the albedo can be reduced by up to 50%," adds Navarro.

As for the Andean glaciers such as Zongo, Navarro recalls that the majority are small, with a very high mountain, "so the effect will be local (affecting water reserves for the hillside communities below), but not global. "Also, as with eruptions, fires are more or less punctual." For glaciers, global warming of the atmosphere with climate change and punctual volcanoes and fires ", complete.

(tagsToTranslate) fire (t) amazon (t) melt (t) Andean glacier (t) soot (t) fire (t) increase (t) solar radiation (t) (t) absorb (t) ice ( t) favor (t) fusion

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