A sediment core which has allowed researchers from the University of Pittsburgh create a 2,300-year climate record reveals that as temperatures rise, so the summer monsoons will become drier.
The 6 foot-long sediment core was retrieved from Laguna Pumacocha in Peru, high up in the Andes Mountains, and contains the most detailed geochcmical record of tropical climate fluctuations ever found. It shows that the planet’s tropical regions will experience severe water shortages as higher temperatures dry up the monsoons which are so critical to life in the tropics.
Already the equatorial regions of South America are receiving less rainfall than at any point in the past millennium.
Together with existing geological data of precipitation changes in the tropics, the sediment core illustrates that rainfall during the South American summer monsoon has dropped significantly since 1990, a shift which has not been seen since the beginning of the sediment cores record in 300BCE.
Mark Abbott, co-author of the study and a professor of geology and planetary science in the University of Pittsburgh’s School of Arts and Sciences who also co-designed the project, said that he and his colleagues had not anticipated the rapid decrease in 20th century rainfall that they observed in the sediment core.
“This model suggests that tropical regions are dry to a point we would not have predicted,” Abbott said. “If the monsoons that are so critical to the water supply in tropical areas continue to diminish at this pace, it will have devastating implications for the water resources of a huge swath of the planet.”
From 300 BCE to 900 CE, the sediment core showed regular fluctuations in rainfall, with a notable heavy period of precipitation in 550 CE. However, starting in the year 900, a severe drought set in for the next three centuries, with the driest period falling between 1000 and 1040 CE. Abbott pointed out that this period of time corresponds to the demise of regional Native American populations, including the Tiwanaku and Wari that inhabited present-day Boliva, Chile, and Peru.
After the year 1300 CE, monsoons became wet again, with the wettest period of the past 2,300 years lasting from approximately 1500 to the 1750s. This took place during a period of time known as the Little Ice Age, a period of time which saw cooler temperatures worldwide.
A dry cycle occurred around 1820 which quickly gave way to a wet phase which itself gave way to a waning of rain in 1900. By 2007, there had been a steep and a steady increase in dry conditions to a high point not surpassed since 1000.
Source: University of Pittsburgh
Image Source: Ian McKenzie