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The Study of Tree Rings and How it Describes Paleoclimate
Nico Sartori
The Ohio State University
GEOG 3900: Global Climate Change
Dr. Bryan G. Mark
October 17, 2022
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I.
Introduction
Earth’s climate is experiencing climate change through human implications, and it is only
going to get worst if nothing is done about it. However, an overall big picture of past climates is
vital to analyze how our climate varies in the future due to global warming. Paleoclimate has
allowed us to study previous climates that have existed during past Earth geologic ages. In order
to determine past geologic ages, paleo proxies are studied to gather indirect climate information
of the past. One primary example are tree rings. In the following section, tree ring methods,
strengths and weaknesses, and description of a case study is explored in analyzing paleoclimate.
II.
Discussion
a. Description of Tree Rings
Tree rings are representative of a tree’s growth each year where each ring are several
concentric circles embarked on the tree trunk. As a result, tree rings explore past environmental
conditions such as physical and biochemical analysis that determine what weather and climate
conditions prolonged during the year the ring was born (Anchukaitis, 2017, p. 244). Several
climate variables impact tree rings such as water, evapotranspiration, relative humidity, soil
moisture, sunlight, or carbon dioxide. Many of these factors can be discovered through the width
of the annual ring (TRW) or density of the wood (MXD) of the most populated indirect climate
archive (Franke et. al, 2020, p. 1061). All of the variables listed above can be revealed through
isotope composition in which an element has a different number of neutrons in their nuclei, but
an equal number of protons. As a result, the oxygen isotope reveals the meteorological and
hydrological source of water by the tree as well as evapotranspiration, relative humidity, and
precipitation. On the other hand, the carbon isotope reveals information about soil moisture,
sunlight, or how much carbon dioxide is currently in the atmosphere. This relates to the carbon
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cycle where the carbon isotope is controlled through photosynthesis through the leaf stomata that
yields a carbonic sugar as well as oxygen (Anchukaitis, 2017, p. 245). Therefore, tree rings allow
scientists to analyze paleoclimatology through hydroclimate variability.
b. Strengths and Weaknesses
While tree rings give us access to historical climate records, the proxy itself can have
many flaws as well as strengths. Starting with the strengths, tree rings are archived across the
midlatitudes usually in the Northern Hemisphere and are dated with precision based upon the
ring’s year of formation. This allows scientists to study variability in climate variables of the
exact timeline of climate anomalies and the overlap between statistics and calibration
(Anchukaitis, 2017, p. 245). As a result, tree rings can have reliable and accurate data as it is
simple to collect and can be easily cloned through an accessible timeline easily determine the
energy budget of the Earth system. In contrast, tree rings also have several weaknesses.
Although they are widespread over the midlatitudes, tree rings cannot produce a global
analysis of the climate regime as the polar and tropic regions are excluded. The tropical regions
tend to be very wet and experience systems such as hurricanes year-round which is affecting
much streamflow around the equator. According to Anchukaitis, “Canadian tree lines are still
under-sampled compared to similar environments in Europe and Asia, which prevents a
complete understanding of the temperature history and variability of North America” (2017, p.
257-258). In another case, the geography and ecology of the Southern Hemisphere also face
more challenges in tree ring archives as many scientists are still trying to answer questions about
radiative forcing and atmospheric dynamics and how that impacts on various timescales
(Anchukaitis, 2017, p. 257). Thus, there is still more work that needs to be done in understanding
paleoclimatology as many case studies are analyzing the effectiveness of tree rings.
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c. Case Study of Tree Rings
Data assimilation is vital in studying the climate field through tree-ring collections and
Jorg Franke from the Institute of Geography from the University of Bern among other scientists
have conducted an experiment. In their study, they used the “Kalman-filter-based state-of-the-art
data assimilation technique” which is time dependent from the external forcing through the
model simulations. They used tree-ring width (TRW) and wood density (MXD) by various
datasets and have discovered that climate signals in tree-ring proxies are more complicated than
a correlation between temperature and precipitation. There are limiting factors and sunlight can
be an important factor, but not always have a direct correlation with temperature. Moreover, a
large proxy collection doesn’t lead to an accurate climate reconstruction while small selections
fail to reconstruct the four-dimensional multivariable atmosphere. Therefore, they concluded that
input data is vital such as taking possible temperature and precipitation limitations of tree growth
factored in, determine the exact tree growth, remove random climate signals, and remove any
human errors (Franke et. al, 2020). As a result, data quality and data quantity seem to have an
inverse relationship when it comes to tree rings.
III.
Conclusion
Tree rings are a representative paleoclimate proxy for climate reconstruction due to easy
collection and statistical record each ring formed every year. However, the proxy fails to depict a
global climate reconstruction regime in which it lacks in the Southern Hemisphere as well as in
the tropics and polar regions. Several case studies have been discussed in improving data quality
and quantity of tree-ring collections but varies the input data. Therefore, tree rings allow
scientists to determine past historical climate records as well as predict the future of climate
change from their results.
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IV.
Bibliography
ANCHUKAITIS, K. J. (2017). Tree Rings Reveal Climate Change Past, Present, and
Future. Proceedings of the American Philosophical Society, 161(3), 244–263.
http://www.jstor.org/stable/45211559
Franke, J., Valler, V., Brönnimann, S., Neukom, R., & Jaume-Santero, F. (2020). The
importance of input data quality and quantity in climate field reconstructions – results
from the assimilation of various tree-ring collections. Climate of the Past, 16(3), 1061–
1074. https://doi.org/10.5194/cp-16-1061-2020