Prof Gustaf Hugelius of the Bolin Centre at Stockholm University warns heatwaves and wildfires could accelerate permafrost thaw across vast regions that hold three times more carbon than all living vegetation. He says melting ground ice creates thermokarsts whose new lakes, wetlands or gullies change hydrology and thermal conductivity so the landscape will not revert for hundreds of years. Hugelius argues the entire permafrost zone will not tip at once unless global warming reaches about 6C, but many local tipping points have already begun and will occur in succession. He estimates a loss of 200 to 300 gigatons of CO2 equivalents if warming reaches between 1.8C and 3.6C by 2100, many times current EU emissions and in higher scenarios approaching present-day US or Chinese annual emissions. Methane released from wet, thawed areas is roughly 30 times more potent over 10 to 15 years, while dry thaw produces CO2 that lingers for centuries, so whether thawed landscapes become wetter or drier is a key unknown. Hugelius says extreme high-methane scenarios are now considered unrealistic and the permafrost source is not expected to exceed all human emissions this century, but there is a decades-long lag and by the end of the century permafrost could become a major net emitter.
