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Tree rings show scale of Arctic pollution is worse than previously thought, EUREKALERT, UNIVERSITY OF CAMBRIDGE, Research News 28 Sept 20, The largest-ever study of tree rings from Norilsk in the Russian Arctic has shown that the direct and indirect effects of industrial pollution in the region and beyond are far worse than previously thought.An international team of researchers, led by the University of Cambridge, has combined ring width and wood chemistry measurements from living and dead trees with soil characteristics and computer modelling to show that the damage done by decades of nickel and copper mining has not only devastated local environments, but also affected the global carbon cycle.

The extent of damage done to the boreal forest, the largest land biome on Earth, can be seen in the annual growth rings of trees near Norilsk where die off has spread up to 100 kilometres. The results are reported in the journal Ecology Letters.

Norilsk, in northern Siberia, is the world’s northernmost city with more than 100,000 people, and one of the most polluted places on Earth. Since the 1930s, intensive mining of the area’s massive nickel, copper and palladium deposits, combined with few environmental regulations, has led to severe pollution levels. A massive oil spill in May 2020 has added to the extreme level of environmental damage in the area.

Not only are the high level of airborne emissions from the Norilsk industrial complex responsible for the direct destruction of around 24,000 square kilometres of boreal forest since the 1960s, surviving trees across much of the high-northern latitudes are suffering as well. The high pollution levels cause declining tree growth, which in turn have an effect of the amount of carbon that can be sequestered in the boreal forest…….

The researchers used a process-based forward model of boreal tree growth, with and without surface irradiance forcing as a proxy for pollutants, to show that Arctic dimming since the 1970s has substantially reduced tree growth.

Arctic dimming is a phenomenon caused by increased particulates in the Earth’s atmosphere, whether from pollution, dust or volcanic eruptions. The phenomenon partially blocks out sunlight, slowing the process of evaporation and interfering with the hydrological cycle.

Global warming should be expected to increase the rate of boreal tree growth, but the researchers found that as the pollution levels peaked, the rate of tree growth in northern Siberia slowed. They found that the pollution levels in the atmosphere diminished the trees’ ability to turn sunlight into energy through photosynthesis, and so they were not able to grow as quickly or as strong as they would in areas with lower pollution levels.

“What surprised us is just how widespread the effects of industrial pollution are – the scale of the damage shows just how vulnerable and sensitive the boreal forest is,” said Büntgen. “Given the ecological importance of this biome, the pollution levels across the high-northern latitudes could have an enormous impact on the entire global carbon cycle.”  https://www.eurekalert.org/pub_releases/2020-09/uoc-trs092420.php