Permafrost Thaw Calculator

Active layer thickness — the depth of soil that freezes and thaws each year above the permanently frozen ground beneath it — is calculated here with the classic Stefan equation, ALT = E × √(degree-days of thawing), in the form formalized for permafrost prediction by Nelson & Outcalt (1987), where the edaphic factor E encodes how quickly heat penetrates a given soil type (gravel conducts heat fastest, peat's insulating organic matter slowest). The calculator runs this twice: once for today's thaw season length and temperature, and once for a warmed scenario in which extra warming both lengthens the thaw season (roughly 8 more days per °C) and raises its average temperature, then reports the increase in active layer depth between the two. That extra thawed soil volume, multiplied by a supplied carbon density and the permafrost area, produces an estimate of how much soil carbon becomes biologically available — for scale, Schuur et al. (2015, Nature) estimate the northern permafrost region holds on the order of 1,300-1,500 billion tonnes of organic carbon in its top 3 metres, roughly twice the carbon currently in the atmosphere, so even a small fraction becoming newly available represents a large absolute quantity; the model splits that carbon into a 97%/3% CO2/methane mix by mass and converts to a single CO2-equivalent figure using methane's 100-year global warming potential of 27.9.

The result is spread evenly across your chosen time horizon to get an annual release rate — a simplification, since real thaw and decomposition rates are not linear over time. A stability indicator based on projected mean annual air temperature flags whether the ground stays continuously frozen (below −2°C), sits in a marginal zone, or is actively degrading. Treat every output as an order-of-magnitude planning estimate: local soil carbon density, drainage, and ice content vary enormously and dominate real-world uncertainty far more than the equation's own math does.