The Rise of the Mongol Empire

Rising in the early 13th century under the ruler Ghengis Khan, the Mongol Empire would become the largest contiguous land empire in history. Tree ring scientists previously found that Mongolia likely experienced a milder, wetter climate during the Empire's initial period of expansion. In the new study, the reconstructed average June-July temperature from 1205-1224 was 0.5 °C (1 °F) warmer than the dataset's mean. During this time, the fertile grasslands of mild, wet summers may have supported increased production of livestock and war horses, literally fueling the Mongols' extraordinary conquest. Read more: Climate and Conquest: How Did Genghis Khan Rise?

Image: Expansion of the Mongol Empire 1206–1294 superimposed on a modern political map of Eurasia. Wikimedia Commons

The Little Ice Age

The Little Ice Age was a period of cooling that occurred from approximately the 15th through the 19th centuries. At different times and places, the climatic effects of the Little Ice Age contributed to periods of social instability that are reflected in the historical record. In East Asia, severe droughts and famine during the 17th century contributed to the collapse of the great Ming dynasty, a successor of the Mongol Empire. The tree ring data at right shows that the interval from 1650-1675 was particularly cold in the study region, averaging nearly 1.5 °C (2.5 °F) cooler than the mean.

Scientists have advanced several possible causes for the Little Ice Age, including decreased solar activity, volcanic eruptions, and fluctuations in the human population.

Image: "The Frozen Thames" by Abraham Hondius, 1677. Wikimedia Commons

Eruption of Krakatoa, 1883

Large volcanic eruptions can affect global climate by emitting huge amounts of ash and sulfur dioxide high into the atmosphere where they block or reflect solar radiation, causing the Earth's surface to cool.

Destroying some 70% of its island and the surrounding archipelago, the eruption of Krakatoa in 1883 was one of the deadliest and most destructive volcanic events in recorded history. In addition to causing global cooling, the atmospheric particles from the eruption produced vivid sunsets throughout the world for many months; a Krakatoa sunset may even be depicted in Edvard Munch's famous painting The Scream. The eruption's signature is also visible in the Mongolian tree ring data, which shows a steep drop in temperature in 1884.

Image: An 1888 lithograph of the eruption of Krakatoa. Wikimedia Commons

Mongolia: Past, Present and Future

Both the tree ring data (blue) and observed temperatures (black) confirm that this region is one of the fastest-warming places on the planet. In just the past 15 years, summer temperatures have warmed 1.6 °C (3 °F) — almost three times the global average rate. This warming has already begun to impact the environment and people of Mongolia: severe winters and droughts in the 2000s resulted in major livestock die-offs and the migration of many nomadic herders to Ulaanbaatar, the capital city.

Projections indicate the region is expected to warm by another 3 to 6 °C (5.4 to 10.8 °F) by the end of the century. This continued warming may exacerbate the desertification, water stress and harsh winter storms that have characterized recent years, reshaping the land and people of Mongolia once again.

Figure: CMIP5 simulations of mean June-July temperatures for Western Mongolia. hover for full captionFigure: CMIP5 simulations of mean June-July temperatures for Western Mongolia over the 1850-2005 ‘historical’ period and 2006-2099 ‘future’ simulation period under two different emission scenarios, RCP 4.5 and RCP 8.5 (in orange). The multi-model median presented is smoothed as a running 15-year average to reduce the impact of random interannual variability in model simulations. The simulations are compared against instrumental observations (in red) and reconstructed (in black) mean June-July temperature. All datasets are plotted relative to their 1960-1990 mean. The shading around CMIP5 simulations is the interquartile range (IQR, i.e. 5th, 50th, and 95th percentiles) across 28 models. | view large version