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Permafrost vulnerability in the context of 1.5 °C and 2 °C warming

In an effort to significantly reduce the risks and impacts of climate change, the long-term goal of the Paris Agreement is “holding the increase in the global average temperature (GMT) to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C”. In this blog post, the impacts of a GMT increase of 1.5 and 2 °C above pre-industrial levels on near-surface permafrost were derived from two pan-Arctic simulations of the 5th generation Canadian Regional Climate Model (CRCM5) - one with dynamic vegetation (DYN, using the Canadian Terrestrial Ecosystem Model) and the other with static vegetation (STAT). Both transient climate change simulations (1950-2100) were performed for the Representative Concentration Pathway 8.5 (RCP8.5), using forcing from CanESM2.

To account for model deviations from observations over the historical period, the 1.5 and 2 °C warming levels are derived relative to the reference period 1986-2005, which is 0.6 °C warmer than pre-industrial levels according to IPCC AR5. This translates to a warming of 0.9 °C and 1.4 °C above reference period levels for the 1.5 °C and 2 °C limits, respectively. For CanESM2 RCP8.5, the 20-year time slice with a GMT increase of 1.5 °C corresponds to 2009-2028, while a GMT increase of 2 °C corresponds to the 2022-2041 time slice.

CRCM5 projections from both simulations, DYN and STAT, suggest that keeping the GMT increase below 2 °C can prevent the degradation of around 40% of the pan-Arctic near-surface permafrost extent, defined as regions containing permafrost in the top 5 m of soil, which is otherwise projected to degrade by the end of the 21st century under RCP8.5. The permafrost closest to the surface (in the top 1 m of soil) is especially vulnerable to warming, but keeping the GMT increase below 2 °C is projected to also prevent the degradation of large areas of this generally carbon-rich permafrost.

Evolution of near-surface permafrost extent during the 21st century (left column). Vulnerability of near-surface permafrost under RCP8.5 in the STAT simulation (center column) and in the DYN simulation (right column). Dark red shading is used for regions where near-surface permafrost degrades before a 1.5 °C increase in GMT. Orange shading is used where near-surface permafrost degrades after a 1.5 °C increase, but before a 2 °C increase in GMT. Yellow shading is used where near-surface permafrost degrades after the 2 °C threshold, but before the end of the 21st century. Green shading is used where near-surface permafrost remains by the end of the 21st century.

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