Dear Friend of CIFAR,

Southern California. Southeastern BC. South East Asia. These areas share a common scar: a legacy of devastating wildfires. As catastrophic as wildfires are on the scale of human experience, they have been an integral part of the Earth system ever since plants first appeared on the surface of the planet about 400 million years ago. Yet we know surprisingly little about how wildfires interact with the Earth system.

My work aims to change that. I study the geochemistry of soils and sediments affected by wildfire. These studies serve as a window into the past – a pursuit of the ancient Fingerprints of Fire.

For example, when soils are heated by wildfire, the mercury in them (which occurs naturally) is lost to the atmosphere and depleted in the burned soil. It turns out that the degree of this depletion correlates with the intensity of the fire. In other words, mercury levels can record periods of widespread or intense burning.

I am working with Earth System Evolution postdoctoral fellow Abir Biswas and program member Lee Kump to study the Fingerprints of Fire for important periods in Earth’s history, including a period called the PETM, 55 million years ago – when rapid climate change similar to today’s was occurring. This period is characterized by a rapid and yet unexplained increase in global temperatures of 6-8 degrees Celsius, enormous additions of carbon to the atmosphere and oceans, and evidence of increased wildfire. These features of the PETM raise questions about exactly how wildfires interact with globally increasing temperatures and changing precipitation patterns.

We are addressing some of these questions by looking at both proximal materials, such as bedrock and fossil soils that are most directly affected by heating, and distal deposits that may record far-traveled residues and geochemical signatures of burning. The depletion of mercury in burned forest soils, for example, indicates that mercury is transported in the air from the fire to deep sea sediments. But the path it takes to reach the sea, and the impact it might have on geochemical cycles there, is not yet clear.

The Intergovernmental Panel on Climate Change report concluded that global climate change will increase the risk of extreme fire events. But there is still much to find out. For example, the IPCC’s assessment did not identify potential fire-climate feedbacks. Some researchers suggest that positive feedbacks exist, and it is possible that during the time of the PETM, burning peat swamps were actually a cause, rather than a consequence, of the dramatic climate change.

Our research into ancient wildfires will help us understand the impact and co-evolution of wildfire with the Earth system over time. It may also shed light on the challenges we currently face in a world of increasing temperatures, changing rainfall patterns and susceptibility to inevitable and increasingly devastating events, such as wildfires.

Best wishes from the frontiers of human knowledge.

Peter Reiners
Fellow, Earth System Evolution program
Canadian Institute for Advanced Research