Something Strange Is Happening to Earth’s Clouds—and It Could Have Unpleasant Consequences

Where are clouds born? The answer is more complex than it seems. Yes, clouds form in the sky or atmosphere. But the vast layer of gases surrounding the planet is unpredictable, where chaotic factors intermingle with predictable ones.

It’s complex and changing. In trying to answer this question, some scientists have encountered an additional problem: the places where clouds form are changing. The area of Earth’s surface where cumulus clouds typically form has shifted and shrunk. This shift has important implications for the planet’s climate and weather.

These results come from two studies published in recent years: one in Climate Dynamics in August 2024, and another in Geophysical Research Letters in May of this year.

Three cloud bands. The first study examined how cloud zones over the oceans in both hemispheres have shifted and contracted over the past 35 years. The researchers focused on three areas: one near the equator—known as the Intertropical Convergence Zone (ITCZ)—and two located in mid-latitudes, between 30 and 60 degrees north and south.

Using data from instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite, the team mapped the areas with the highest cloud cover and tracked how those regions have changed over time.

Interpreting the data. According to NASA, storm clouds tend to form at the boundaries of large-scale atmospheric circulation zones, such as Hadley cells, polar cells, and Ferrel (mid-latitude) cells. More specifically, storm clouds develop in areas where the currents associated with these cells converge, forcing warm, moist air upward.

Conversely, divergence zones—where cold, dry air from the upper atmosphere descends—tend to have clearer skies.

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A change in trend. Studying clouds provides insight into the dynamics of these storm-prone planetary regions. For example, the research team calculated that the cloud-dense area has contracted between 1.5% and 3% per decade.

According to NASA, the ITCZ has narrowed, and stormy areas in mid-latitudes have shifted toward their respective poles while also contracting. In contrast, the clear subtropical regions have expanded.

More than just a question of color. The most recent study explores the climate implications of global cloud pattern changes. Earth’s climate depends heavily on the clouds that obscure the atmosphere and occasionally turn it white. This cloud layer affects how much solar energy reaches the surface by influencing albedo—the planet’s reflectivity.

Clouds reflect light and therefore solar energy, so fewer clouds mean more heat reaches the surface. According to the study’s estimates, this change means oceans are absorbing 0.37 more watts per square meter per decade.

But what about climate change? We might assume this shift explains the warming trend associated with human-driven climate change. However, climate models already account for these cloud changes. Previous estimates by NASA’s Clouds and the Earth’s Radiant Energy System (CERES) instruments suggest the planet receives an additional 0.47 watts per square meter per decade.

These changes contribute to the “energy imbalance” that causes global warming, but they don’t fully explain it. “These new findings suggest that the loss of oceanic storm clouds is a key driver of the imbalance,” George Tselioudis, a member of the research team, said in a NASA statement.

According to Tselioudis, these changes could also help explain the unusual ocean warming that occurred a couple of years ago and led the North Atlantic to break several temperature records.

Image | Billy Huynh (Unsplash)

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