Ancient climate records reveal how East Asian monsoon shifted abruptly into cold and drought

Researchers from Utrecht University in the Netherlands, along with colleagues in China and Belgium, have examined ancient climate records to understand how the East Asian monsoon system underwent abrupt shifts into cold and drought conditions. Over a period of 250,000 years, they discovered that the monsoon's behavior is influenced by changes in incoming solar radiation, which varies due to Earth's orbit and tilt.

However, when this radiation drops below a critical threshold and atmospheric CO₂ levels are low, the monsoon can experience extreme and prolonged cold and dry spells. Professor Francien Peterse, a co-author of the study, emphasized the importance of understanding this relationship as over a fifth of the world's population relies on the monsoon for freshwater.

Traditionally, studying past monsoon dynamics has been challenging as conventional methods combine temperature and precipitation data, making it hard to differentiate between them. To overcome this, the researchers developed a technique using subtle variations in the molecular structure of soil bacteria, which react differently to temperature and precipitation changes.

By analyzing fossil membrane molecules from a sediment sequence on the Chinese Loess Plateau, they found that both temperature and precipitation followed changes in solar radiation over long periods, but occasionally, extreme cold and dry periods occurred, lasting for several millennia. These extreme events happened when solar radiation fell below a specific level, a threshold identified previously in a study by a co-author.

The climate only returned to normal once solar radiation increased again. While these ancient events do not directly predict current climate extremes, they provide valuable insights into how solar radiation can trigger abrupt climate responses.