Climate Secrets from Antarctic Ice

A New Perspective on Historical Fire Activity

Let’s do an experiment, shall we? Imagine you are a climate scientist (trust me, it’s so much fun!). Well, you are collecting data to perform a statistical climate model.

When we perform a statistical model, we need some ingredients, but primarily, we need a question or variable we want to predict. For example, what will the concentration of greenhouse gases be in 10, 50, or 100 years, or what may mean average temperatures look like?

How do we calculate this? Well, first of all, we need historical data on the variables that we are trying to measure, such as the concentration of greenhouse gases in the atmosphere or past temperatures.

But then, we need something equally important. These variables that we are trying to predict depend on other variables, too, some for which we may also have past information. So, we need to collect this data. Then, our statistical analyses will help us predict responses based on ancient patterns.

Easy, right?

Well, not always. Sometimes, for one reason or another, there is one variable that we don’t have data for. This could be for many reasons, but usually, it is because we either (1) don’t have the technology to obtain this data or (2) we are confident we can make an assumption on how this variable has changed over time.

However, and luckily, researchers nowadays are trying to avoid assumed variables and ensure all are properly calculated.

Now, back to the experiment. What would you say if I asked you whether wildfires have steadily increased over the last 200 years? I imagine most of you, myself included, would say they have indeed steadily increased.

Well, a team of researchers wanted to make sure this was a real assumption, so they got hands-on and traveled to our beloved Antarctica, one of the coldest places on Earth, to find out…

By studying carbon monoxide (CO) trapped in Antarctic ice, researchers from the University of Cambridge and the British Antarctic Survey have managed to piece together a record of biomass burning that stretches back nearly two centuries. Their findings are not just another piece of the climate puzzle — they’re reshaping our understanding of how fire activity has evolved in the Southern Hemisphere and challenging some long-held assumptions in climate science. Yes, those pesky assumptions again.

The research, recently published in the Proceedings of the National Academy of Sciences (PNAS), focuses on carbon monoxide — a gas released during biomass burning, such as wildfires and cooking fires. The scientists extracted this gas from ice cores, which are long cylinders of ice drilled out from the Antarctic ice sheet.

These cores contain layers of ice formed as the snow was compacted year after year, each layer capturing tiny bubbles of air that offer a direct sample of the atmosphere from when the snow originally fell.

The challenge with measuring gases like CO from more recent times lies in the fact that the ice hasn’t been under pressure long enough to fully trap these gases.

However, the researchers selected ice cores from regions with high snow accumulation rates to tackle this. The faster snow piles up, the quicker it compresses, and the more rapidly it forms those critical air bubbles. This approach allowed them to gather a continuous record of atmospheric CO from 1821 to 1995, covering the preindustrial era to the brink of the 21st century.

So, what did they find? Well, contrary to what many might expect, the study showed that biomass burning in the Southern Hemisphere has been much more variable over the past 200 years than previously thought. For instance, while one might assume that fire activity increased alongside population growth and industrialization, the data tells a different story. The research indicates that after an initial increase, fire activity began to decline around the 1920s.

This drop in fire activity coincides with significant land-use changes across regions like southern Africa, South America, and Australia — areas where wildlands were rapidly converted into farmland. Once forests were burned down, there wasn’t much left to burn anymore.

Forests were cleared as these landscapes were transformed, and fire activity naturally decreased. Dr. Rachael Rhodes, a senior author of the paper from Cambridge’s Department of Earth Sciences, pointed out, “This trend reflects how land conversion and human expansion have negatively impacted landscapes and ecosystems, causing a major shift in the natural fire regime and, in turn, altering our planet’s carbon cycle.”

However, these findings are more than just an interesting historical footnote — they have real implications for the climate models that scientists use to predict future changes. But why?

Many models, including those used by the Intergovernmental Panel on Climate Change (IPCC), have operated under the assumption that fire activity has consistently increased with population growth. And it’s easy to understand why they made this assumption.

However, this research suggests that the models may need to be adjusted to better reflect the actual variability in fire activity over the past two centuries.

Just imagine, if the models predicted catastrophic events assuming that carbon sources came from forest fires, what would be the reality now that we know that these fires were not contributing as much as we though? In other words, now that we know that the increase in greenhouse gases that we are observing doesn’t necessarily come from increased forest fires.

The take-home message here is clear, though: our planet’s fire history is more complex than we thought, and understanding it better will help improve the tools we use to forecast, prevent, and adapt climate change. By filling in gaps in our knowledge with data like this, scientists can refine their models, ultimately leading to more accurate predictions and better strategies for managing the impacts of climate change.

Knowledge makes us stronger and more effective!

But even more, this research reminds us of how interconnected our environment is—how changes in one part of the world, like land use in the Southern Hemisphere, can have far-reaching effects on the global climate system. It’s also a call to reexamine some of the assumptions we’ve made about how human activities have shaped our planet’s past and how they will continue to shape its future.