The climate turning point may already be a reality in East Asia

University of Gothenburg

The climate in inland East Asia may already have reached a tipping point, where the transition in recent years to unusually hot and dry summers may be irreversible. This is the result of a new international study by researchers from the University of Gothenburg now published in Science.

Associated with ongoing global warming, it is changes that impact regional climate and ecosystems. At worst, these can reach what is known as a tipping point, at which point the changes are rapid and often irreversible. Examples of hotspots are the disappearance of sea ice in the Arctic in the summer or the melting of the Greenland ice sheet.

Inner East Asia is a sensitive area

Inner East Asia, which includes Mongolia and neighboring areas, is a sensitive region that has seen a sharp increase in the number of heat waves during the summer in recent decades. Together with stable high-pressure systems, which raise temperatures, reduced soil moisture can cause intense and lasting heat waves due to the increased interaction between the earth’s surface and the atmosphere.

“The appearance of this connection in a longer pre-industrial context is, however, unknown as there are no long-term observations,” says Deliang Chen, co-author of the study and leader of the Regional Climate Group (RCG) at the University of Gothenburg.

The annual growth rings of trees provide information about the changes that affect their growth and this can be used to study climate change in the past.

“By choosing trees whose growth is sensitive to weather changes, annual rings can be used to reconstruct different climate parameters with annual resolution hundreds of years back in time. Because trees have significant geographic coverage, these data can be used for detailed climate change studies over large areas, ”says Hans Linderholm, study co-author and head of the Gothenburg University’s Laboratory of Dendrochronology (GULD).

The study of tree rings has shown that a turning point is near

Long-term observations of soil moisture are rare, but tree rings, which are limited by access to water, can be used as indicators of this parameter. Similarly, trees that grow at high altitudes, where the growing season is short and cool, can be used to provide temperature information.

“In this study, we developed a new method to reconstruct both variations in soil moisture and changes in the frequency of heat waves in Inner East Asia, a region where the interaction between these parameters is very strong,” says Peng Zhang, first author of the study and a researcher in the Regional Climate Group at the University of Gothenburg.

These new reconstructions allow scientists to study the recent hot, dry summers in a long-term perspective. The results show that the current high frequency of heat waves and low soil moisture have not been observed in the past 260 years.

“By combining observations, reconstructions and climate model data, we found that the link between the earth’s surface and the atmosphere has become more pronounced in Inner East Asia over the past 20 years, along with more drying of soils. So we argue that reduced soil moisture improves earth-atmosphere coupling by contributing to the warming of the earth’s surface, which causes more heat waves, which in turn reduces soil moisture and so on, “Peng says.

The study authors found that the recent pattern of increased warming and drought indicates that a turning point in climate is near, a change that could be irreversible and lead to a much drier climate in the region.

“This would increase the stress on ecosystems and societies in this already vulnerable region,” says Peng.