Timescales of the permafrost carbon cycle and legacy effects of temperature overshoot scenarios

Philipp De Vrese,Victor Brovkin

doi:10.1038/s41467-021-23010-5

Philipp De Vrese, Victor Brovkin

Open Access

https://doi.org/10.1038/s41467-021-23010-5

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Abstract

Minimizing the risks and impacts of climate change requires limiting the global temperature increase to 1.5 °C above preindustrial levels, while the difficulty of reducing carbon emissions at the necessary rate increases the likelihood of temporarily overshooting this climate target. Using simulations with the land surface model JSBACH, we show that it takes high-latitude ecosystems and the state of permafrost-affected soils several centuries to adjust to the atmospheric conditions that arise at the 1.5 °C-target. Here, a temporary warming of the Arctic entails important legacy effects and we show that feedbacks between water-, energy- and carbon cycles allow for multiple steady-states in permafrost regions, which differ with respect to the physical state of the soil, the soil carbon concentrations and the terrestrial carbon uptake and -release. The steady-states depend on the soil organic matter content at the point of climate stabilization, which is significantly affected by an overshoot-induced soil carbon loss.

Highlights

Minimizing the risks and impacts of climate change requires limiting the global temperature increase to 1.5 °C above preindustrial levels, while the difficulty of reducing carbon emissions at the necessary rate increases the likelihood of temporarily overshooting this climate target
To this end we investigate simulations—with prescribed atmospheric conditions—that target the state of the northern permafrost regions (Fig. 1a) after reaching the PACT1.5 by different climate trajectories (Fig. 1b and Supplementary Fig. 5): without prior OS and after three different OS scenarios that are based on SSP5-8.5 and assume forcing-peaks in the years 2050, 2075, and 2100, respectively
The modeling results presented here indicate that these observable changes do not depict the entire impacts due to the committed climate change

Summary

Introduction

Minimizing the risks and impacts of climate change requires limiting the global temperature increase to 1.5 °C above preindustrial levels, while the difficulty of reducing carbon emissions at the necessary rate increases the likelihood of temporarily overshooting this climate target. The carbon concentrations below the active layer reflect the state of the ecosystem at the time the respective soil region was incorporated into the permafrost This state is determined by the antecedent climate trajectory, making it possible that a temporary warming would affect the amount of organic matter stored within the perennially frozen fraction of the soil, changing the emission budget for a given temperature target[16,17,18]. It is an open question whether an OS could entail long-lasting legacy effects for the Arctic ecosystem that go beyond the amount of stable permafrost carbon, affecting soil temperatures, the soil water content or even primary productivity and soil respiration. We use simulations with JSBACH, the land surface component of the Max-Planck-Institute for Meteorology’s Earth system model MPI-ESM1.241, to explore the timescale on which the Arctic ecosystem adjusts to the atmospheric conditions that result from climate stabilization at a Paris-Agreementcompliant temperature target (PACT1.5)— at

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