In a discovery that could reshape climate models, scientists have pinpointed a surprising biological origin for the delicate, high-altitude veils known as cirrus clouds. The research, led by Dr Benjamin Murray from the University of Leeds, overturns long-held assumptions about how these clouds form and suggests their impact on global warming may be more significant than previously thought.
The Unexpected Role of Biological Particles
For decades, the scientific consensus held that cirrus clouds, which form in the frigid upper troposphere, were seeded primarily by mineral dust or metallic particles. These act as ice-nucleating particles (INPs), providing a surface for ice crystals to form in the supercooled vapour of the atmosphere. However, the new study, published in the journal Nature Geoscience, presents compelling evidence that a substantial portion of these crucial particles are, in fact, biological in nature.
The international research team, which included scientists from the UK, Germany, and Switzerland, conducted a series of sophisticated experiments. They analysed air samples collected at high altitude over a period of several years. Using advanced spectrometry and microscopy techniques, they were able to identify the chemical and physical signatures of the particles that served as the nuclei for ice crystals.
The results were startling. A significant fraction of the effective INPs were composed of organic materials consistent with fragments of plants, fungi, bacteria, and pollen. These biological remnants, lofted high into the atmosphere by winds and storms, were proving to be remarkably efficient at triggering ice formation at the extreme cold temperatures found at cirrus levels.
Implications for Climate Modelling and Global Warming
This finding is far from an academic curiosity; it has profound implications for predicting future climate change. Cirrus clouds play a complex dual role in Earth's energy balance. While they reflect some incoming solar radiation back into space, they also act as a potent blanket, trapping long-wave infrared heat radiating from the Earth's surface. On balance, their net effect is one of warming.
Current climate models, which largely assume mineral-based nucleation, may be underestimating both the abundance and the warming influence of cirrus clouds. "If biological particles are more effective at forming ice crystals under certain conditions, they could lead to more cirrus clouds than our models predict," explained Dr Murray. This means the planet's natural cloud feedback mechanisms could be different, potentially amplifying global warming.
The research also opens a new frontier in understanding how changes on the Earth's surface—such as deforestation, agricultural expansion, or even shifts in fungal spore production due to warmer temperatures—could indirectly influence high-altitude cloud cover and, consequently, the global climate.
A New Chapter in Atmospheric Science
The study marks a pivotal shift in atmospheric science. It connects the biosphere—the realm of living organisms—directly to one of the most important processes in the upper atmosphere. The team's next steps involve expanding the geographic scope of their sampling and integrating their findings into sophisticated global climate models to quantify the precise impact.
Dr Susannah Burrows, a co-author from the Pacific Northwest National Laboratory in the US, emphasised the importance of this holistic view: "Our atmosphere is not a separate system. This shows us that life on the surface can reach up and influence the very highest clouds, with consequences for us all." The research underscores the intricate and often unexpected linkages within the Earth's climate system, highlighting a critical new factor that must be accounted for in the urgent task of forecasting our planet's future.
