The first human activities had a bigger impact than expected on the Earth’s atmosphere

Several years ago, while analyzing ice core samples from James Ross Island in Antarctica, scientists Joe McConnell, Ph.D., and Nathan Chellman, Ph.D., of DRI, and Robert Mulvaney, Ph.D., of the British Antarctic Survey noticed something unusual: a substantial increase in carbon black levels that began around AD 1300 and has continued to the present day.

Carbon black, commonly referred to as soot, is a light absorbing particle that comes from combustion sources such as biomass burning (e.g. forest fires) and, more recently, the burning of fossil fuels. Working in collaboration with an international team of scientists from the United Kingdom, Austria, Norway, Germany, Australia, Argentina and the United States, McConnell, Chellman and Mulvaney set out to uncover the origins of the unexpected increase in carbon black captured in the Antarctic Ice.

The team’s findings, published this week in Nature, point to an unlikely source: ancient Maori land-burning practices in New Zealand, carried out on a scale that impacted the atmosphere in much of the southern hemisphere and eclipsed other pre-industrial emissions from the region over the past 2,000 years.

“The idea that humans at this time in history caused such a large change in atmospheric carbon black through their land clearing activities is quite surprising,” said McConnell, a research professor of hydrology at DRI who has designed and led the study. “We used to think that if you went back a few hundred years back you would be in front of a pristine pre-industrial world, but it is clear from this study that humans have an impact on the environment beyond. over the Southern Ocean and the Antarctic Peninsula for at least the past 700 years. “

Trace carbon black to its source

To identify the source of the carbon black, the study team analyzed a set of six ice cores collected from James Ross Island and mainland Antarctica using the unique continuous analytical system of ice cores from DRI. The method used to analyze carbon black in ice was first developed in McConnell’s lab in 2007.

While the James Ross Island ice core showed a noticeable increase in black carbon starting in 1300, with levels tripling over the next 700 years and peaking in the 16^e and 17^e centuries, black carbon levels at sites in mainland Antarctica over the same period have remained relatively stable.

Andreas Stohl, Ph.D., University of Vienna led simulations of atmospheric models of black carbon transport and deposition around the southern hemisphere which supported the results.

“From our models and the Antarctic deposition model seen in the ice, it is clear that Patagonia, Tasmania and New Zealand were the most likely points of origin for the increase in emissions of black carbon from around 1300, ”Stohl said.

After looking at the paleofire records from each of the three regions, there was only one viable possibility left: New Zealand, where charcoal records showed a significant increase in fire activity from l around 1300. This date also coincided with the estimated arrival, colonization and subsequent burning. much of New Zealand’s forested areas by the Maori people.

This was a surprising finding, given New Zealand’s relatively small area and the distance (almost 4,500 miles) that the smoke would have traveled to reach the ice core site on James Ross Island.

“Compared to natural burning in places like the Amazon, Southern Africa or Australia, you wouldn’t expect Maori burning in New Zealand to have a big impact, but it does on the Southern Ocean and the Antarctic Peninsula, ”said Chellman, postdoctoral fellow at DRI. “Being able to use the ice core recordings to show the impacts on atmospheric chemistry that reached the entire Southern Ocean, and being able to attribute this to the arrival and settlement of the Maori in New Zealand 700 years ago was Truly unbelievable.”

Research impacts

The results of the study are important for a number of reasons. First, the results have important implications for our understanding of Earth’s atmosphere and climate. Modern climate models rely on accurate information about the past climate to make projections for the future, particularly on emissions and light-absorbing black carbon concentrations related to the Earth’s radiation balance. Although it is often assumed that human impacts in pre-industrial times were negligible compared to background or natural combustion, this study provides new evidence that emissions from human combustion impacted the atmosphere. terrestrial and perhaps on its climate much earlier, and on much larger scales, than previously imagined.

Second, the fallout from biomass combustion is rich in micronutrients such as iron. The growth of phytoplankton in much of the Southern Ocean is limited in nutrients, so the increased fallout from the Maori fires has likely resulted in centuries of increased phytoplankton growth in large areas of the southern hemisphere.

Third, the results refine what is known about the time of Maori arrival in New Zealand, one of the last habitable places on earth to be colonized by humans. Maori arrival dates based on radiocarbon dates vary from 13^e to 14^e century, but the more precise dating made possible by ice core records indicates the start of a large-scale burn by the early Maori in New Zealand until 1297, with an uncertainty of 30 years.

“From this study and other previous work our team has done, such as the 2,000-year-old lead pollution in the Arctic from ancient Rome, it is clear that the records of ice cores are very valuable in knowing more about past human impacts on the environment, ”said McConnell. noted. “Even the most remote parts of the Earth were not necessarily pristine in pre-industrial times.”