Humans had an impact on the Himalayas long before a person ever set foot on them, research suggests.
A new study, published in the journal PNAS, has found that by-products of burning coal in Europe in the late 18th century made their way to the Dasuopu glacier, which is 7200 metres above sea level on Shishapangma, the world’s 14th highest mountain.
Shishapangma was first climbed in 1964.
Ice cores were drilled at the glacier (making them the highest ever collected) back in 1997, and these provide a record of snowfall, atmospheric circulation and other environmental changes over time.
Recently Paolo Gabrielli from Ohio State University, US, and colleagues analysed one of the cores – containing ice they believe formed between 1499 and 1992 – looking for signs of 23 trace elements.
They found higher-than-natural levels of a number of toxic metals, including cadmium, chromium, nickel and zinc, from around 1780 – the start of the Industrial Revolution in the UK.
These metals are all by-products of burning coal. They were likely transported by winter winds, which travel around the globe from west to east.
The researchers say it also is possible some of the metals, notably zinc, came from large-scale forest fires, including those used in the 1800s and 1900s to clear trees for farms.
“What happens is at that time, in addition to the Industrial Revolution, the human population exploded and expanded,” Gabrielli says. “And so there was a greater need for agricultural fields and, typically, the way they got new fields was to burn forests.”
The contamination in the ice core was most intense from about 1810 to 1880. Gabrielli says that is likely because winters were wetter than normal in Dasuopu during that period, meaning more ice and snow formed.
That ice and snow would have been contaminated by fly ash from the burning of coal or trees that made its way into the westerly winds – and greater quantities of contaminated ice and snow means more contamination on the glacier.
Gabrielli stresses that it is important to note the difference between “contamination” and “pollution”.
“The levels of metals we found were higher than what would exist naturally but were not high enough to be acutely toxic or poisonous,” he says.
“However, in the future, bioaccumulation may concentrate metals from meltwater at dangerous toxic levels in the tissues of organisms that live in ecosystems below the glacier.”