Climate change is one of the most pressing challenges of our time, as it affects the Earth's natural systems and human societies in various ways.
However, to understand the causes and consequences of climate change, we need to have reliable and long-term records of past climate variability and trends.
One of the sources of such records is tree rings, which can reveal the temperature and precipitation history of a region for hundreds or thousands of years.
A recent study by researchers from Switzerland has used tree rings to show that it has not been this warm in the past 1,200 years in Scandinavia.
The study was published in the journal Nature.
How tree rings can reveal past temperature and precipitation history
JEAN-FRANCOIS MONIER/AFP via Getty Images
Tree rings are concentric circles that can be seen in a cross-section of a tree trunk.
Each ring represents one year of growth, and the width and density of each ring depend on the environmental conditions that the tree experienced during that year, as per Phys.org.
For example, a wide ring indicates a favorable year with abundant water and nutrients, while a narrow ring indicates a stressful year with drought or cold.
By measuring and analyzing the width and density of tree rings, scientists can reconstruct the climate history of a region for as long as the trees have been growing.
Tree rings are especially useful for reconstructing temperature and precipitation, which are two key variables for climate change studies.
Temperature affects the length of the growing season and the rate of photosynthesis, while precipitation affects the availability of water and soil moisture.
By comparing the tree ring records with instrumental measurements of temperature and precipitation, scientists can calibrate their models and extend their reconstructions beyond the period of direct observations.
The unprecedented warming in Scandinavia over the past 1,200 years
The researchers used a new method to reconstruct the summer temperatures in Scandinavia for the past 1,200 years based on tree rings, as per The Washington Post.
The method involved measuring the cell wall thickness of the wood cells in each annual ring, which is directly proportional to the temperature during the growing season.
The researchers used this method to analyze 188 living and dead Scots pines (Pinus sylvestris) from Sweden and Finland, whose annual rings spanned from 800 to 2019 CE.
The results showed that the current warming is unprecedented during this period, as none of the previous centuries had temperatures as high as those observed in recent decades.
Themere was no evidence of a Medieval climate anomaly, which is a period of unusually warm temperatures that occurred between 950 and 1250 CE in some regions of the world, according to the study.
Scientists found that the Medieval climate anomaly was cooler than previously thought in Scandinavia, at least based on their tree ring records.
The study's result also agreed with climate model simulations, which showed only moderately warm temperatures for the Medieval climate anomaly in Scandinavia.
This suggested that previous reconstructions based on other methods, such as the density or width of tree rings, may have overestimated the Medieval warmth due to other factors that influenced their growth.
The implications and applications of the study for climate change research and prediction
The study has several implications and applications for understanding and predicting climate change in Scandinavia and other regions of the world.
First, it provides a high-quality and long-term record of summer temperatures in Scandinavia that can be used for further research and validation of climate models.
Second, it reveals some of the natural variability and trends of climate in Scandinavia over the past 1,200 years, which can help identify the drivers and patterns of climate change in this region.
Third, it shows that the current warming is outside the range of natural fluctuations in temperatures over this period, which implies that it is mainly caused by human activities such as greenhouse gas emissions.
The study also demonstrates a novel and precise method to extract temperature information from tree rings based on cell wall thickness measurements.
This method can be applied to other regions and species where long-term tree ring records are available or can be obtained.
It can also complement other methods based on density or width measurements to improve the accuracy and resolution of temperature reconstructions.
