In a discovery that could reshape our understanding of the atmosphere and climate change, scientists have pinpointed a surprising and previously overlooked origin for the wispy, high-flying cirrus clouds that blanket our skies.
Unexpected Particles at High Altitude
The research, published in the journal Science Advances, reveals that a significant portion of these delicate clouds form around tiny particles lofted from the Earth's surface, not just from the freezing of ambient water vapour as long assumed. These particles, known as ice-nucleating particles, act as seeds around which ice crystals form at the frigid temperatures found miles above the ground.
Led by atmospheric scientist Dr. Paul DeMott from Colorado State University, the international team used data from NASA's airborne campaigns, including the ACCLIP mission over South Korea in 2022. They employed a specialised instrument, the Portable Ice Nucleation Experiment (PINE) chamber, to analyse air samples collected at altitudes where cirrus clouds live.
Challenging Established Climate Models
The findings directly challenge the assumptions built into many leading global climate models. For decades, these models have largely simulated cirrus cloud formation based on the idea that ice crystals nucleate spontaneously from cooled water vapour. This new evidence shows that terrestrial and marine particles play a far more crucial role than previously recognised.
"This changes our perception of which sources of particles are important for cirrus cloud formation," explained Dr. DeMott. The study suggests that dust, microbes, and sea spray aerosols from Earth's surface can be transported to the upper troposphere, where they initiate cloud formation. This process has major implications because cirrus clouds have a complex effect on climate: they can trap heat, contributing to warming, but also reflect sunlight.
Implications for Future Climate Predictions
Understanding the true mechanics of cirrus cloud formation is critical for accurate climate forecasting. If models have been incorrectly simulating how these clouds are born, their projections of future global warming may be inaccurate. The research indicates that as the climate changes, the sources and quantities of these ice-nucleating particles may also shift, creating a feedback loop that current models do not fully capture.
"We need to revisit how we represent ice nucleation in these high clouds in climate models," stated Dr. Christina McCluskey, a co-author of the study from the National Center for Atmospheric Research. The team's work underscores a significant gap in our atmospheric knowledge and highlights the need for more direct observational data from the elusive regions where cirrus clouds form.
This breakthrough discovery means that to predict the future climate with greater certainty, scientists must now look down to the Earth's surface as much as they look up at the skies, re-evaluating the invisible connections that shape our planet's delicate atmospheric balance.
