When the atmosphere slows the Earth: Uncovering a subtle signal of climate change

Atmospheric circulation shapes weather and climate, and it also transfers angular momentum. When winds change or mass redistributes, the atmosphere can redistribute momentum with the Earth, slightly altering its rotation rate. This concept is not new, but what happens during long-term global warming was unclear. Previous studies suggested an increase in atmospheric angular momentum (AAM), but the reason was unknown: stronger winds or a deeper atmospheric restructuring?

To answer this, researchers conducted large-ensemble climate simulations from three global models under a high-emissions scenario. They found that changes in atmospheric circulation, well-known responses to warming, systematically increase AAM. Simultaneously, surface momentum exchange between the atmosphere and Earth weakens, reducing Earth's efficiency in keeping up with the changing atmosphere.

This results in a faster-moving atmosphere and a slower-rotating Earth. The changes are subtle, with the increase in the length of day (LOD) due to atmospheric changes reaching about 10%–18% of the long-term tidal friction trend by the end of the 21st century. This is significant because tidal friction has traditionally been considered the dominant driver of long-term rotational slowing.

However, core-mantle interactions dominate Earth's rotation variability on decadal to centennial timescales. Thus, atmospheric changes are an additional, climate-driven component within the broader rotational system. The study highlights that global warming is reorganizing atmospheric circulation in a way that measurably influences Earth's rotational dynamics, positioning atmospheric changes as an additional, climate-driven component in this complex system.

This discovery emphasizes that climate change is reshaping the fundamental dynamical balance of the Earth system, with the atmosphere, oceans, cryosphere, and solid Earth tightly coupled, with changes in one component inevitably propagating into others, sometimes in unexpected ways.