Human activity has weakened wind patterns

September 19 () –

Human activity has been identified as the cause of a weakening of air circulation systems, that help spread and disperse moisture and heat throughout the world

The summer of 2024 was the hottest on record, and unfortunately, this was no surprise. Summers have become hotter and drier around the world, including the Northern Hemisphere, which has caused intense droughts and heat waves in North America and Europe and poses serious risks to society, such as wildfires, crop failures and health hazards.

Part of the problem is that Earth’s air circulation systems have been weakening over the years. However, The exact reasons for this weakening have eluded researchers.

Now, in two studies led by Dr. Rei Chemke of the Weizmann Institute of Science, researchers have managed to decipher this mystery: Human activity is what has weakened the air circulation systems.

Both studies focused on wind patterns that together act as a vital network through which wind-borne heat and moisture flow around the world. An important part of this network are storm tracks, the high- and low-pressure weather systems that flow from west to east.

Together, these storms have a significant impact on the transfer of heat, moisture, and momentum of airflow within the atmosphere, which in turn affects the different climatic zones of the Earth.

The second part is the Hadley circulation, in which warm air builds up at the equator and flows toward the poles, descends to the surface in the subtropics, and returns to the equator, continuing the cycle.

While both storm tracks and the Hadley circulation have been weakening since at least 1980, Only the weakening of the Hadley circulation had been linked to human-induced emissions..

GREENHOUSE GASES AND AEROSOLS

In a study with Professor Dim Coumou of the Vrije Universiteit Amsterdam, Chemke demonstrated for the first time that the weakening of storm tracks is due to man-made emissions of greenhouse gases such as CO2 and aerosols.

“These emissions warm the air more at high latitudes than at low latitudes,” Chemke says. in a statementAs a result, the temperature difference between northern and southern latitudes, which is what drives storm tracks in the first place, has narrowed, and this reduction has led to a weakening of storm tracks.

To reach this conclusion, the scientists analyzed massive amounts of climate data from both observations and advanced climate models. Only when historical emissions were included in the climate model calculations could the observed weakening be explained. These findings were published in npj Climate and Atmospheric Science.

“Summer storms play an important role in bringing cold air from the ocean to land,” Chemke said. “If you reduce the intensity of these storms, you bring in less cold air. This leads to a buildup of warm temperatures over the continent, which may lead to increasingly extreme heat events.”

NATURAL EFFECTS STRENGTHENED HER

Human-caused emissions are also affecting the Hadley circulation in a historically unprecedented way: compared to the impact of natural factors in the past, their effect is greater in magnitude and works in the opposite direction, i.e. weakening this circulation rather than strengthening it.

That is the conclusion of the second study, published in Nature Communicationswhich Chemke, who works in Weizmann’s Department of Earth and Planetary Sciences, carried out with his student Or Hess.

“We don’t have wind records from the last millennium, so we can’t just look at past wind patterns and compare them to current ones, but there is a good reconstruction of the factors that drive climate systems,” Chemke said. “These factors are used to simulate past climate in models that encapsulate all the physics, biology and chemistry of the climate system.”

Using these model simulations, Chemke and Hess were able to investigate how natural factors, such as volcanic eruptions and solar fluxes, modified the Hadley circulation over past centuries.

They found that these natural factors acted to strengthen the Hadley circulation over the past millennium, in stark contrast to the current and ongoing weakening of this circulation. These results suggest that Human-caused emissions have reversed a naturally induced strengthening of the flow.

“In the previous millennium, natural factors were dominant, whereas now, human-caused emissions play a more dominant role,” Hess said. “In the past, we had a cooling climate that acted to strengthen the Hadley circulation. Today, we have a warming climate that acts to weaken this circulation.”