The intensification of winter mid-latitude storm tracks in the Southern Hemisphere

Study key findings & significance

• The effects of climate change have heavily intensified winter storms in the Southern Hemisphere to a level that computational climate models had only previously projected for the year 2080.
• After simulating storm intensification patterns under isolated natural climate fluctuations, the research team found that storms over the past two decades have been intensifying faster than can be explained by these natural processes alone.
• The researchers determined that physical changes in atmospheric jet streams over the past 20 years are linked to the escalating nature of these Southern Hemisphere winter storms, which are not accurately reflected in current climate models.
• The results of the study suggest that climate projections for the coming years are perhaps more grim than prior assessments have predicted and indicate that human activity yields a greater impact on the Southern Hemisphere than previous estimates.

Author quotes

“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 lower.”

“We chose to focus on the Southern Hemisphere because the intensification registered there has been stronger than in the Northern Hemisphere. 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, we will be observing more significant winter storm intensification here in the upcoming years and decades.”

Rei Chemke, lead author and scientist at the Weismann Institute of Science

Abstract

The strength of mid-latitude storm tracks shapes weather and climate phenomena in the extra-tropics, as these storm tracks control the daily to multi-decadal variability of precipitation, temperature and winds. By the end of this century, winter mid-latitude storms are projected to intensify in the Southern Hemisphere, with large consequences over the entire extra-tropics. Therefore, it is critical to be able to accurately assess the impacts of anthropogenic emissions on these storms to improve societal preparedness for future changes. Here we show that current climate models severely underestimate the intensification in mid-latitude storm tracks in recent decades. Specifically, the intensification obtained from reanalyses has already reached the model-projected end-of-the-century intensification. The biased intensification is found to be linked to biases in the zonal flow. These results question the ability of climate models to accurately predict the future impacts of anthropogenic emissions in the Southern Hemisphere mid-latitudes.