Secrets of the Past Hidden in the Leaves

By
Patrick Cho
June 16, 2020

C+S 2020 students are blogging about topics that interest them for Applications in Climate and Society, a core spring class.


Leaves are basically solar panels for plants, helping them harvest the sun’s energy to grow. But they also serve as secret climate record keepers. Specifically, the thin layer of wax covering them that prevent excess water from being lost. This is what is known as the cuticle layer.

Hidden within these waxy layers are records of climate information about the world such as rain and plant type of the time period. In developing nations that are highly dependent on precipitation for their well-being, having information about how ainfall patterns may change with the evolving climate is crucial. Scientists may get hints of this information by looking to the past using proxies or hints such as leaf waxes.

Glorified Espresso Machine

As leaves fall to the ground and eventually degrade, the organic compounds that are the foundation of the cuticle get left behind. The leaf wax deposits can get piled up along with sediment in bodies of water such as deltas and fans. As layers of sediment including leaf wax pile up over time, these compounds are very resilient to degradation and stay intact. Scientists can go out to these areas and drill cores, extracting hundreds of meters of sediment at once. Millions of years of climate records are hidden within the leaf wax in these cores.

Scientists can extract the leaf wax compounds in a very similar fashion to how a barista extracts a shot of espresso. Just like baristas run hot, pressurized water through coffee grounds to extract espresso, scientists use different organic chemicals to extract leaf wax compounds from the sediment.

Just as a trained palate can tell the origins of coffee by taste, scientists can use specialized instruments to reveal secrets of the past rainfall and vegetation through the extracted leaf wax compounds. These instruments will look at the ratio of the hydrogen and carbon isotopes, which in turn give us hints about rainfall and vegetation respectively. From this, we can see how the Earth’s climate has changed in the distant past.

Believe it or Not… tHis iS hElPfUl!

Climate scientists can use this information to learn about how the Earth behaves during times of rapid climate change. That’s vital right now, as human activities have pumped carbon dioxide into the atmosphere at a very rapid rate, reaching levels unseen in millions of years. When we look to the past and natural changes in the climate tied with natural carbon dioxide shifts, we can learn a little bit about possibilities of what could happen in the future due to the current unnatural situation.

This information is crucial for people like farmers who are highly dependent on climate and weather patterns for their well-being. Nations such as India, Bangladesh and Myanmar in particular are reliant on rainfed agriculture and the Asian Monsoon, a key weather pattern that has shifted in the past and shows signs of changing in the present. By using leaf wax, we can look at time periods of past rapid climate change and see how rainfall patterns changed. This gives scientists ideas of how our world may change in the future.

We need to learn as much as we can and as fast as we can to understand what is to come.