New climate model predicts harder winters, stronger storms

A team of scientists led by Dr. Rei Chemke of the Weizmann Institute’s Department of Earth and Planetary Sciences revealed that there has been a considerable intensification of winter storms in the Southern Hemisphere, occurring far earlier in the century than previous models predicted. The study, conducted in collaboration with Dr. Yi Ming of Princeton University and Dr. Janni Yuval of MIT, is sure to make waves in the climate conversation.

Until now, climate models have projected a human-caused intensification of winter storms only toward the end of this century. In the new study, Dr. Chemke and his team compared climate model simulations with current storm observations. Their discovery was bleak: It became clear that storm intensification over recent decades has already reached levels projected to occur in the year 2080.

“A winter storm is a weather phenomenon that lasts only a few days. Individually, each storm doesn’t carry much climatic weight. However, the long-term effect of winter storms becomes evident when assessing cumulative data collected over long periods of time,” Dr. Chemke explains. Cumulatively, these storms have a significant impact, affecting the transfer of heat, moisture and momentum within the atmosphere, which consequently affects the various climate zones on Earth.

“One example of this is the role the storms play in regulating the temperature at the Earth’s poles. Winter storms are responsible for the majority of the heat transport away from tropical regions toward the poles. Without their contribution, the average pole temperatures would be about 30°C [86°F] lower,” he adds. Similarly, the collective intensification of these storms yields a real and significant threat to societies in the Southern Hemisphere in the next decades.

“We chose to focus on the Southern Hemisphere because the intensification registered there has been stronger than in the Northern Hemisphere,” Dr. Chemke says. “We didn’t examine the Northern Hemisphere, but it seems that the intensification of storms in this hemisphere is slower compared to that in the Southern Hemisphere. If the trend persists,” Dr. Chemke adds, “we will be observing more significant winter storm intensification here in the upcoming years and decades.”

In this study, published in Nature Climate Change in May 2022, Dr. Chemke and his research partners sought to understand whether these changes in climate patterns were caused by external factors (such as human activity), or whether they have resulted from the internal fluctuations of the global climate system. They analyzed climate models that simulated storm intensification patterns under the isolated influence of internal climatic causes, without external impact. They showed that over the past 20 years, storms have been intensifying faster than can be explained by internal climatic behavior alone.

In addition, the researchers discovered the physical process behind the storm intensification. An analysis of the growth rate of the storms showed that changes in atmospheric jet streams over the past few decades have caused these escalations, and current climate models are unable to reflect these changes accurately.

The study has two immediate, considerable implications. First, it shows that not only climate projections for the coming decades are graver than previous assessments, but it also suggests that human activity might have a greater impact on the Southern Hemisphere than previously estimated. This means that rapid and decisive intervention is required in order to halt the climate damage in this region. Second, a correction of the bias in climate models is in order, so that these can provide a more accurate climate projection in the future.

Dr. Rei Chemke’s research is supported by the Willner Family Leadership Institute for the Weizmann Institute of Science, and the Zuckerman STEM Leadership Program.