Emily Cai

With the onslaught of increasingly frequent floods and storms brought about by climate change, Yale researchers pointed to a possible culprit: the changing course of mighty “atmospheric rivers” in the sky.

The study was spearheaded by Flint postdoctoral associate Seung Hun Baek and assistant professor of earth and planetary sciences Juan Lora. Their work was published in the journal Nature Climate Change on Oct. 4, and it was the culmination of the team’s analysis of 85 years of climate data and existing simulations conducted by the National Center for Atmospheric Research. 

“We want to better understand how the water cycle in the atmosphere has evolved over the last several million years,” Lora said. “Extreme precipitation will change in the future, and that is of huge importance to people worldwide as the atmosphere warms.”

According to Baek, the volatile levels of precipitation that have characterized the 21st century are partly the result of intensifying atmospheric rivers –– winding columns of intense water vapor that transport more water than the discharge of 27 Mississippi Rivers. AR activity correlates with rising temperatures associated with global warming, since warm air holds more water vapor, he said. 

However, despite climate change having existed since the 1920s, increasing activity has only been observed in the more recent years. The influence of greenhouse gas emissions, which contribute to atmospheric warming and humidification, is accelerating and will soon dominate that of industrial aerosols, which have an opposite cooling and drying effect that curbs the intensity of ARs, Lora said. Prior to 2005, the levels of greenhouse gases and industrial aerosols have been approximately equal, “cancel[ing] out … atmospheric rivers that you would see from global warming,” according to Baek. 

Lora said that the study’s results should be alarming to policymakers and people worldwide, with particularly drastic effects on Europe, South America, coastal regions and middle latitudes, where major storms will witness increased frequency and intensity. 

“This phenomenon can happen anywhere where you have the intersection of dramatic amounts of moisture from the tropics and waves from the pole,” said postdoctoral fellow Michael Battalio, who is not part of this study, but participates in other hydrologic cycle projects as part of Lora’s lab. 

Battalio cited the “1000-year floods” in Texas as an example, saying they are happening more frequently than they statistically should.

Lora did note, however, that it is important to consider the “detriment to benefit” ratio of ARs and explained that we should not view them as completely harmful. For example, in some drier areas such as southern California, historically known for having severe water shortages, the presence of ARs can make or break a drought. 

In terms of potential solutions to intensifying AR activity, Battalio said that the warming has “already baked in.” Instead, he emphasized that humans should be working on mitigation strategies: reducing greenhouse gas emissions –– CO₂ in particular — transitioning to renewable resources like wind and solar energy, ensuring that future infrastructure is “robust” and providing developing nations with the appropriate technology to mitigate reliance on fossil fuels.

“This is not a faraway problem,” Battalio said. “This is going to be my generation, my children’s generation, and grandchildren’s children. People are already dying. People are already suffering in the United States, one of the most developed countries in the world.” 

To further bring light to this nearing reality of climate change risks, Baek and Lora are hopeful to explore forces that impact ARs aside from greenhouse gases and aerosols, as well as using large ensembles of simulations to better understand the background variability of a climate system and its relationship with ARs.

The complete publication, titled “Counterbalancing influences of aerosols and greenhouse gases on atmospheric rivers,” can be viewed here.