The ice-albedo feedback is one of the most powerful amplifying mechanisms in the climate system. It creates a positive feedback loop: warming melts ice, exposing darker surfaces that absorb more solar radiation, causing further warming.
This simulator models the feedback explicitly. Surface albedo α(T) varies linearly between the high albedo of ice (~0.7) at temperatures below -10°C and the low albedo of dark ocean/land (~0.12) at temperatures above 20°C. The energy balance equation C·dT/dt = S(1-α(T))/4 + F - σT⁴ is integrated forward in time, where C is ocean heat capacity and F is external forcing.
The feedback factor f measures the amplification: it is the ratio of equilibrium warming with feedback to warming without feedback (where albedo is held fixed). For realistic parameters, f ranges from 1.5 to 2, meaning the ice-albedo mechanism roughly doubles the warming from CO₂ alone.
Manabe and Wetherald (1967) were among the first to model this feedback in a general circulation model, showing that polar regions warm disproportionately — a prediction confirmed spectacularly by observations of Arctic amplification. The Arctic has warmed 2-4 times faster than the global average since the 1970s.
The feedback has a threshold character that makes it particularly concerning. As long as ice exists, the feedback operates. But below a critical temperature, it can drive the system toward 'Snowball Earth' — a state where runaway ice growth covers the entire planet. Geological evidence suggests this happened at least twice, around 717 and 635 million years ago. The escape mechanism was volcanic CO₂ accumulation over millions of years, eventually overwhelming the high-albedo ice.
In the modern context, the relevant threshold is the disappearance of Arctic summer sea ice, which may occur within the next few decades. Once summer ice is gone, this particular feedback channel saturates in the Arctic, though Antarctic ice sheets remain vulnerable on longer timescales.