New method of analyzing tree rings confirms unprecedented warming in Central Asia
Baatarbileg Nachin and Brendan Buckley collected a tree ring core from 1250 Siberian larch. The photo was taken in August 1998. Image Credit: Neil Pederson
A relatively new method of annual ring analysis allows researchers to reconstruct the temperature in Mongolia since 1269 AD. The new reconstruction confirms that since the 1990s, summer temperatures have been the warmest in the region in the past eight centuries.
Published on Geophysical Research Letters, The study was created by Nicole David, A part-time senior research scientist at Columbia University’s Lamont-Dougherty Earth Observatory.
Central Asia is one of them The fastest temperature rise Places on earth. In the past 15 years alone, summer temperatures have risen by 1.59 degrees Celsius, or close to 3 degrees Fahrenheit—almost three times the global average temperature. During the same period, the area suffered extreme and prolonged drought.
To date, there are only a few long-term climate records in Central Asia that can help bring these trends into context.Analyzing the growth rings of trees can tell scientists Temperature and precipitation pattern Hundreds or thousands of years ago, but appropriate old trees and logs in the area may be difficult to sample, partly because of their remoteness.
The scarcity of tree ring data in this area makes new reconstruction work particularly important. To create it, David and her colleagues analyzed tree ring cores originally collected for projects led by her mentor in 1998 and 2005. Gordon Jacoby, Co-founder of Lamont Tree Ring Lab. Jacoby has been trying to use the ring width to reconstruct the temperature history of the area, but the data is not strong enough, so he put it aside. Before Jacoby died in 2014, David asked for permission to take over the project.
The map of Mongolia shows the locations of the stations included in the study (BU, KK, and OZN, represented by triangles). The blue and red dots indicate the weather station that recorded the temperature. Image source: Davi et al./Geophysical Research Letters 2021
The samples came from several high-altitude forests in western Mongolia. “People think it is this vast grassland system, but there are some extraordinary ancient forests all over the country, and they are very primitive,” David said. She added that these locations are very remote. “To reach these forests is a considerable expedition.”
A video clip recorded by Gordon Jacoby shows one of the study sites and the surrounding vegetation and landscape.
The core comes from living Siberian larch trees and residual woods dating back 400 to 500 years-old trees that have fallen but not decayed due to cold and dry conditions. Davi said: “When we found waste wood, it was very exciting because we knew we could go back even further.”
She wanted to make full use of the sample. Since the ring width model has not yet been completed, the team decided to try a different analysis method: measuring the density of the wood. This is done by taking a very thin tree core-thinner than human hair-and shining light through it. More light will penetrate the less dense rings, and the less dense rings indicate colder growth conditions. Davi and her team tried this method, but unfortunately, she said: “It’s expensive, it takes a lot of time, and it’s very destructive. It destroys the core and we can’t get what we need.”
Finally, the team turned to a newer method, which was put into use a few years ago and showed encouraging results. This method is called delta blue intensity, and it looks at the degree to which each ring reflects blue light in its late wood (the darker band formed later in the growing season) compared to the lighter early wood. The less dense wood produced due to colder conditions absorbs less blue light.
The stronger results from the delta blue light technology allowed the team to build a model of the summer temperature in the region from 1269 AD to 2004. The reconstruction matches data from regional weather stations dating back to the 1950s and related cooling events, accompanied by several large-scale volcanic eruptions.
The history of tree rings
Using the tree ring data from the new study, the image on the right reconstructs the average temperature in western Mongolia from June to July from 1178 to 2004, in degrees Celsius. The following slides explore the different historical events reflected in the data and the climate trends during these periods.
Use the navigation below or slide/drag to advance the slideshow. Chart control: click to adjust size, mouse wheel to zoom, click and drag to pan. View a larger version of this slide.
Next: The rise of the Mongol Empire »
The rise of the Mongol Empire
Rising under the ruler Genghis Khan in the early 13th century, the Mongol Empire will become the largest land empire in history. Tree-ring scientists have previously discovered that in the early days of the empire’s expansion, Mongolia may have experienced a milder and wetter climate. In this new study, the reconstructed average temperature from 1205 to June to July 1224 is 0.5°C (1°F) higher than the average of the data set. During this time, the fertile grasslands of mild and humid summers may have supported the increase in livestock and war horse production, and provided the impetus for the extraordinary conquest of the Mongols. read more: Climate and Conquest: How did Genghis Khan rise?
Picture: The expansion of the Mongol Empire from 1206-1294 is superimposed on the modern political map of Eurasia. Wikimedia Commons
Little Ice Age
The Little Ice Age was a cooling period that occurred approximately between the 15th and 19th centuries. At different times and places, the climate impact of the Little Ice Age led to periods of social instability reflected in historical records.In East Asia, severe drought and famine in the 17th century contributed to The fall of the Ming Dynasty, The successor of the Mongol Empire. The annual ring data on the right shows that the study area from 1650 to 1675 was particularly cold, with an average of nearly 1.5°C (2.5°F) lower than the average.
Scientists have proposed several possible reasons for the Little Ice Age, including reduced solar activity, volcanic eruptions, and population fluctuations.
Picture: “The Frozen River Thames” by Abraham Hondius, 1677. Wikimedia Commons
Krakatau volcano erupted in 1883
Large-scale volcanic eruptions will block or reflect solar radiation by emitting large amounts of volcanic ash and sulfur dioxide into the atmosphere, thereby affecting the global climate and causing the earth’s surface to cool.
The Krakatau volcano eruption in 1883 destroyed about 70% of its islands and surrounding archipelago, making it one of the deadliest and most destructive volcanic events on record. In addition to causing global cooling, atmospheric particles produced by volcanic eruptions have produced vivid sunsets around the world for months; Krakatau’s sunset may even appear in Edward Munch’s famous paintings That screamThe characteristics of this volcanic eruption can also be seen in Mongolian tree ring data, which shows that the temperature dropped sharply in 1884.
Picture: Lithograph from the Krakatau volcano eruption in 1888. Wikimedia Commons
Mongolia: Past, Present and Future
Both the tree ring data (blue) and the observed temperature (black) confirm that this area is one of the fastest warming places on earth. In the past 15 years, summer temperatures have risen by 1.6 °C (3 °F)—almost three times the global average temperature. This warming has already begun to affect Mongolia’s environment and people: the severe winter and drought in the 2000s caused a large number of livestock deaths, and many nomads moved to the capital, Ulaanbaatar.
Forecasts indicate that by the end of this century, the region is expected to heat up another 3 to 6°C (5.4 to 10.8°F). This continued warming may exacerbate the desertification, water stress and severe winter storms that have occurred in recent years, and once again reshape Mongolia’s land and people.
Picture: CMIP5 simulates the average temperature from June to July in western Mongolia. Hover for full titleFigure: CMIP5 simulation of the average temperature of western Mongolia from June to July during the “historical” period from 1850 to 2005 and the “future” simulation period from 2006 to 2099. Under two different emission scenarios, RCP 4.5 and RCP 8.5 (orange) . The median of the multiple models presented is smoothed to a 15-year running average to reduce the impact of random interannual changes in the model simulation. Compare the simulation with instrument observations (red) and reconstructed (black) June-July average temperatures. All data sets are plotted relative to average values from 1960 to 1990. The shadows around the CMIP5 simulation are the interquartile range (IQR, the 5th, 50th, and 95th percentiles) of the 28 models. | View large version
For David, publishing these findings is of great significance to individuals. “Gordon Jacoby is my PhD supervisor, mentor and friend,” she said. “We went on field trips together and went through a lot of adventures. It definitely feels good to end some of the research he started.”
Davi said these findings support the increasing potential of the delta blue intensity method to improve our understanding of past climates. They also brought the warming of Central Asia into the background and strengthened their predictions. According to this prediction, the region is expected to warm by another 3 to 6 degrees Celsius (5.4 to 10.8 degrees Fahrenheit) by the end of this century.Rapid warming is already damaging fragile ecosystems and causing destructive Livestock loss For the herders who have traditionally formed the backbone of Mongolia’s economy.
One of the forests sampled in the study.Source: Gordon Jacoby’s video
“What does this mean for Mongolia’s livelihood?” David asked. “This is a major agricultural culture. Some people live in cities, but some are nomads who have lived in the same way for thousands of years. This reconstruction undoubtedly adds to the warming and global climate models of the past few decades. The background shows what it will look like in the future.”
The document recommends continued investment in infrastructure and climate adaptation programs, such as index-based livestock insurance, to help communities cope with changing conditions.
The co-authors of this new study include several members of the Tree Ring Laboratory at Columbia University’s Lamont-Dougherty Earth Observatory – Mukund Rao, Robert Wilson, Laia Andreu-Hayles, Rose Oelkers, Rosanne D’Arrigo, Baatarbileg Nachin, Brendan Buckley and Caroline Leland-as well as Neil Pederson of Harvard University and Byambagerel Suran of Mongolian National University.
