‘Flying rivers’ hamper Arctic ice recovery – 02/14/2023 – Environment

Climate change has affected rainfall systems around the world, with some extreme events, such as prolonged droughts and heavy rainfall, happening more and more in recent years.

In addition to the damage caused in densely populated places, in plantations and on the slopes of hills, the very heavy rains —which can be the effect of the so-called “flying rivers”—also affect the atmospheric systems at the poles.

A new study points out that these changes have also affected the recovery of ice in the Arctic Ocean, which suffers from melting in the summer, with the highest temperatures, and fails to recover in the winter, when flying rivers are more frequent.

The research was published last February 6 in the specialized journal Nature Climate Change (from the Nature group) and was led by scientists from the Pennsylvania State University (USA). Researchers from the University of California, Los Angeles, and Columbia University (NY) also participated.

Flying rivers are horizontal transports of water masses in the form of steam. They can travel thousands of kilometers, carry energy to other systems and cause heavy rainfall.

In general, flying rivers form in atmospheric systems around the world at medium and high levels — and can carry a very high volume of water, similar to that of Amazonian rivers.

The presence of flying rivers in the Arctic was already known —scientists first described this phenomenon in the eastern Arctic region more than ten years ago—, but the description of their effects on polar ice was only possible through the analysis of images from satellite taken by NASA, the American space agency.

Pengfei Zhang, first author of the study and an assistant professor of meteorology and climatology at Pennsylvania State University, said measurements were previously difficult to make because, with seasonal changes in the sea ice surface, it was not possible to place a device to measure the loss of ice area.

The study then looked at the frequency of flying rivers over the last 40 years (from 1979 to 2021) in the oceanic region of the Arctic (i.e., the ice caps and polar glaciers, not the Arctic mainland) and compared the ratio of water (sea ) and ice in two seasons: summer (June to August) and winter (November to January).

Although temperatures in the region are permanently low, in summer they reach the positive mark, while in winter they reach zero or below – when the freezing point occurs.

Thus, the proportion is of greater melting in the summer, with recovery of part of the frozen cover in the winter. However, in the last 20 years, the proportion has become negative, indicating that there is more water loss than ice recovery.

“In winter the ice is expected to recover, but as soon as there was a slight increase in the ice area, the arrival of another flying river caused this growth to stop, and it was like that until the proportion of water expanded to the whole region. southern region of the Arctic Sea in recent years,” explains Zhang.

“The Arctic temperature in the summer will always be above freezing and in the winter below zero, but what we see is that it is much warmer now than it was 40 years ago.”

According to the researcher, there is also a change with direct effects on the possibility of absorbing solar energy. “Water in the Arctic open sea is darker, with greater absorption of solar energy, while water that is trapped in ice reflects light. Thus, the greater the concentration of water in the sea due to melting ice and the less that is contained in glaciers, more solar energy will be absorbed in spring and summer”, he says.

Another point investigated by the study was whether this difference in the proportion of sea and ice was a direct consequence of human action (global warming) or natural phenomena of atmospheric systems.

“We generated mathematical models to estimate whether the frequency of atmospheric rivers was caused by intrinsic factors [como as correntes pacíficas] or extrinsic [como o aquecimento global]. More than two thirds [68%] were due to direct human influence, that is, global warming, and only 32% were caused by the natural variability of atmospheric systems”, he says.

Zhang also points out that the effects of the increased frequency of flying rivers affect both natural ecosystems and human activities.

“On the one hand, there is a direct effect on human activity, with increased shipping lanes in the Arctic Ocean. [devido ao degelo]. But this is a specific point in view of the challenges that this brings to ecosystems, starting, for example, with populations of polar bears, which will have less and less ice area to hunt seals”, he explains.

The climatologist claims that there is only one way to curb this growth: to adopt aggressive measures to mitigate global warming.

“If we don’t act now, that proportion of ice to sea that has already been lost will not be regained. Some climate scientists predict that in 20 or 30 years there will be no ice in the Arctic summer.”

_{The Planeta em Transe project is supported by the Open Society Foundations.}