Industrial revolution, which played a major role in the rise of capitalism and mass-urbanisation across the world, is also perceived as a starting point of the ongoing warming of our globe. But now, it turns out we may have been off the mark as far as that perception is concerned.
A new analysis of ice core samples from Antarctica’s James Ross Island has revealed substantial levels of black carbon, which was seemingly deposited there in the 1300s—a long time before industrialisation came into the picture. Scientists soon realised that all this soot is a consequence of biomass burning. So it’s safe to say that we humans weren’t much of a party 700 years ago either.
McConnell, research professor of hydrology at DRI, who designed and led the study, said: “The idea that humans at this time in history caused such a significant change in atmospheric black carbon through their land clearing activities is quite surprising.
“We used to think that if you went back a few hundred years you’d be looking at a pristine, pre-industrial world, but it’s clear from this study that humans have been impacting the environment over the Southern Ocean and the Antarctica Peninsula for at least the last 700 years.”
Pursuing the black carbon’s trail
After observing these levels of black carbon deposits, scientists Joe McConnell and Nathan Chellman from DRI, and Robert Mulvaney from the British Antarctic Survey, began to wonder what their source might have been.
Further analysis of the samples from James Ross Island showed a significant increase in black carbon beginning around 1300, with levels tripling over the next 700 years and peaking during the 16th and 17th centuries. But during the same period, the black carbon levels in continental Antarctica remained relatively stable.
By running atmospheric simulations of black carbon transport and deposition in the Southern Hemisphere, the researchers narrowed down three potential black soot sources.
“From our models and the deposition pattern over Antarctica seen in the ice, it is clear that Patagonia, Tasmania, and New Zealand were the most likely points of origin of the increased black carbon emissions starting about 1300,” said Andreas Stohl of the University of Vienna.
The next step was to examine the paleofire records of the shortlisted sources. The only possibility that remained was New Zealand; the charcoal records suggested a significant rise in fire activity around the year 1300. This was also the projected date of the Māori people’s arrival, settlement, and subsequent burning of most of the forested areas in New Zealand.
The results were surprising given the distance between the country and site from where the ice core samples were collected in James Ross island was over 7000 km.
“Compared to natural burning in places like the Amazon, or Southern Africa, or Australia, you wouldn’t expect Māori burning in New Zealand to have a big impact, but it does over the Southern Ocean and the Antarctic Peninsula,” said Chellman, a postdoctoral fellow at DRI.
Implications of the findings
The present study kind of changes our perspective of the Earth and climate. It provides new evidence that emissions from human-related burning have impacted Earth’s atmosphere and possibly its climate far earlier and at scales far larger than previously thought.
“From this study and other previous work our team has done, such as on 2,000-year-old lead pollution in the Arctic from ancient Rome, it is clear that ice core records are very valuable for learning about past human impacts on the environment,” McConnell said.
Remains from biomass-burning that were rich in iron probably led to phytoplankton development in the nutrient-limited regions of the Southern Ocean.
Additionally, the results also clarify what we already knew about the arrival of the Māori. Māori arrival dates, based on radiocarbon evidence, range between the 13th and 14th centuries. However, ice core data allow for a more exact date, indicating the commencement of large-scale burning by early Māori in New Zealand to 1297, with a 30-year uncertainty.
The study was published in Nature this week and can be accessed here.
For weather, science, and COVID-19 updates on the go, download The Weather Channel App (on Android and iOS store). It’s free!