The Mystery of Green Sahara's Collapse
From the last ice age until around 6000 years ago, the region now known as the Sahara Desert was a lush, green landscape teeming with life. This “African Humid Period” ended abruptly, transforming this thriving region into the arid desert seen today. Scientists have long puzzled over how the slow changes in solar radiation due to variations in Earth’s orbit could lead to an abrupt large-scale climate transition, as evidenced in the paleoclimate record and recent model simulations. This mystery highlights the broader challenge of understanding and predicting abrupt shifts in natural systems—commonly linked to tipping points.
Natural systems, such as Earth’s climate, often exhibit nonlinear dynamics and feedback mechanisms that can lead to abrupt and potentially catastrophic regime shifts. These shifts, or tipping points, are difficult to predict with current methods that rely on oversimplified assumptions. New research by Andreas Morr and Niklas Boers, researchers at Technical University of Munich and the Potsdam Institute for Climate Impact Research, introduces advanced early detection methods that provide more accurate and reliable early warnings, particularly under more realistic external conditions.
New approach reveals what happened
Traditional methods assume that random disturbances in a system are uncorrelated in time, modelling them as “white noise”. However, this is not realistic for climate systems, because it assumes each day's weather is independent of the previous day. In reality, tomorrow's weather depends on today's, and this dependence is better represented by "red noise," which captures these connections. This mismatch reduces the reliability of conventional methods for early warning signals. The new method by Morr and Boers addresses this limitation by developing estimators of system stability designed specifically for red noise conditions, which represent the climate system more realistically.
The researchers applied their methods to simulations of an abrupt climate shift in Earth’s past, specifically the desertification of the West Sahara about 6000 years ago. They found a clear early warning before the loss of vegetation, consistent with the crossing of a tipping point.
“Our findings suggest that the abrupt end of the African Humid Period was likely caused by a weakening of the system's stability as the orbital configuration of the Earth changed, gradually pushing the system toward a tipping point”,
says Andreas Morr.
What does this mean?
This finding has important implications for early detection of other tipping points in the climate system. Niklas Boers explains.
“The advanced detection method that we developed enhances our ability to monitor and respond to potential tipping points in various natural systems. Our results suggest that large-scale climate tipping events such as this can in principle be anticipated, hopefully enabling timely interventions”.
By improving the accuracy of early warning signals, the research supports better preparedness and response strategies, ultimately helping us to protect ecosystems and human societies from severe impacts of potential climate tipping points that might be crossed due to anthropogenic climate change.
The full research paper is published in the Physical Review X journal of the American Physical Society and can be accessed here.
