Abstract
The ‘Compost Bomb’ instability refers to a proposed uncontrolled increase in soil temperature. This instability is caused when sufficiently rapid atmospheric warming increases soil heterotrophic respiration which, in turn, heats the soil further. This generates a runaway effect in which soil temperatures rise rapidly. We investigate this process, neglected in Earth system models, but which has thus far been analysed with a conceptual model using ordinary differential equations. That model is deliberately idealised without any representation of the spatial structure of soils. We confirm using a partial differential equation framework, this runaway effect still occurs when accounting for soil depth. Using this newer representation we investigate the forcing parameters that make soils vulnerable to this instability. In particular, we discover that the effect of dangerously large seasonal cycle variations in air temperature can create plausible conditions for a ‘compost bomb’ thermal instability.
Highlights
Coupled climate-carbon cycle Earth system models (ESMs) show that rising temperatures will cause carbon cycle feedbacks that accelerate global warming further [1]
The compost bomb instability is based on the idea that heterotrophic respiration in the soil is both an exothermic reaction [18] and a reaction whose rate increases with temperature
We model soil temperature as a reaction-diffusion system, in which heat is generated by heterotrophic respiration and diffused vertically
Summary
Coupled climate-carbon cycle Earth system models (ESMs) show that rising temperatures will cause carbon cycle feedbacks that accelerate global warming further [1]. A key aspect of heterotrophic respiration, ignored by ESMs [3], is that due to respiration being an exothermic reaction, the released heat must raise the temperature of the soils it occurs in. The LC10 model assumes a single pool of carbon, rather than a spatially extended distribution, which might increase the possibility for a compost bomb. There is the possibility of rate-induced tipping by the sinusoidal variations in air temperature caused by the diurnal and seasonal cycles We investigate those possibilities here, to see if there exist features of these oscillations that may raise the risk of a compost bomb
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