How Scientists are Utilizing Woody Cells to Refine Climate Models

 Lucy Troy

How Scientists are Utilizing Woody Cells to Refine Climate Models

       Can trees offer a glimpse into a past as important as our future?

In the wake of our rapidly changing climate, scientists constantly look to climate models to predict how our climate will continue to change and what measures we must take to prevent the drastic, negative developments associated with this change. These climate models are often refined based on historic climatic patterns, by testing how accurately the models can reflect previously observed climate and weather conditions. 

But observed climate conditions have not been formally recorded continuously since the beginning of time. Thus, the crucial field of dendrochronology – the scientific study of tree rings – emerged. For decades, scientists have observed how the thickness of growth rings vary from year to year. Astronomer Andrew E. Douglass was the first to link ring thickness to climatic patterns, after observing consistent ring width patterns (i.e thin one year then thick the next) in the pines at his Arizona field sites. His students eventually found temperature and precipitation to be the two main factors impacting ring width.

Image courtesy of NASA’s Global Climate Change program

Though tree rings offer a useful overview of historic climatic patterns, the often overlooked width of a ring and the woody cells that comprise it reflect more detailed, crucial information about our climate over past growing seasons. Researchers have begun analyzing the anatomy of woody cells to track shifts in temperature and precipitation throughout these growing seasons, allowing them to look more closely at variations over shorter time windows rather than the entire growing season. This, in turn, allows them to paint a more detailed picture of past climate trends and to gauge the validity of climate models meant to predict future trends. 

Scientist Irina Panyushkina was one of the first to utilize woody cells to analyze these patterns more closely. She spent the late ‘90s analyzing thin slices of tree wood to see how cellular growth rates correlate with temperature. Through a painstaking process of photographing each individual slice under a microscope, importing the images into a computer, and clicking on every single cell to measure it, she was able to create a 350 year climate chronology. She found that total cell counts in each ring closely correlated with mean June temperature, and that cell wall thickness, especially in those cells within the ring that formed just before autumn, was a close estimate for July to September temperatures. 

Thanks to new advances in analytical computer software, we can now complete work like Panyuskina’s in a matter of days, obtaining even more data in the process. This came with the development of a software called ROXAS, which can identify and measure cells from scans of tree rings. With the new explosion in woody cell dendrochronology studies, methods for analysis have been continuously refined, from using wood density calculated from cell size and thickness to tracking fluctuations in cellular measurements. 

Sample analysis by ROXAS of a woody cell within the cross-section of a branch

Using the latter method, dendroclimatologist Kristina Seftigan hopes to add to her North American dataset spanning from 1585-2014 by reconstructing temperatures dating back 1,000 years ago. This time period, known as the Medieval Climate Anomaly, is often considered the closest historical example to the warm period we are experiencing now. Comparing how the climate behaved then to now may reveal how much our modern climate behaves outside of natural variability. Indeed, analyzing woody cells can offer more nuanced data not presented in current climate models, which will consequently allow us to improve those models and effectively prepare for a variety of scenarios resulting from human-caused climate change. 

McDermott, A. (2022). Study of wood cells helps bring past climates to life. The Proceedings of 

the National Academy of Sciences, 119(29). https://doi.org/10.1073/pnas.220963611