Clues to future climate change effects found in Antarctica

A novel investigation of smoke particles trapped in Antarctic ice spanning back hundreds of years may reveal the planet’s future climate change effects.

The study, led by Harvard University and international researchers from the Desert Research Institute and the University of Hong Kong, analysed centuries-old smoke particles from the Southern Hemisphere, which has revealed its fiery history, possibly signifying the Earth’s future climate change effects.

The findings are published in Science Advances.

Pengfei Liu, the first author of the paper, said: “Up till now, the magnitude of past fire activity, and thus the amount of smoke in the pre-industrial atmosphere, has not been well characterised. These results have importance for understanding the evolution of climate change from the 1750s until today, and for predicting future climate.”

When predicting future climate change effects, the most significant variable is the impact of greenhouse gases on surface temperatures – a highly arduous calculus of competing warming and the atmospheres cooling effects. Heat is cocooned in the atmosphere by greenhouse gases, which subsequently raises the planet’s surface temperature; contrastingly, fires, volcanoes, and various combustion create aerosol particles that cool the world by obstructing sunlight. A comprehensive understanding of these processes can aid in predicting future climate change effects.

While traditional models utilise greenhouse gases and aerosols to estimate possible effects, they do have an inherent flaw; pre-industrial levels of greenhouse gases are well understood, whereas smoke aerosols are not. To combat this lack of data and model the Southern Hemisphere, the team analysed Antarctica, as smoke particles from fires in Africa, Australia, and South America is still preserved in the ice. The researchers measured soot in 14 ice cores throughout the continent.

Joseph McConnel, a co-author of the study, said: “Soot deposited in glacier ice directly reflects past atmospheric concentrations, so well-dated ice cores provide the most reliable long-term records.”

Loretta Mickley, a Senior Research Fellow in Chemistry-Climate Interactions at SEAS and senior author of the paper, said: “While most studies have assumed less fire took place in the pre-industrial era, the ice cores suggested a much fierier past, at least in the Southern Hemisphere.”

To simulate these levels of smoke, the scientists recreated them using computer models, accounting for indigenous burning practices and wildfires.

“The computer simulations of fire show that the atmosphere of the Southern Hemisphere could have been very smoky in the century before the Industrial Revolution. Soot concentrations in the atmosphere were up to four times greater than previous studies suggested. Most of this was caused by widespread and regular burning practised by indigenous peoples in the pre-colonial period,” said Jed Kaplan, Associate Professor from the Research Division of Earth & Planetary Science at the University of Hong Kong and co-author of the study.

The results corresponded with the ice core records, demonstrating that soot was present before the inception of the industrial era, remaining reasonably constant throughout the 20th century, signifying that as changes increased fire activity, industry emissions increased. The scientists believe that previous models over-estimated carbon dioxides warming effect and other greenhouse gasses to account for the observed increases in surface temperatures.

Liu said: “Climate scientists have known that the most recent generation of climate models have been over-estimating surface temperature sensitivity to greenhouse gasses, but we haven’t known why or by how much.”

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