The Climate Benefit of Carbon Sequestration

Carlos Sierra,Holger Metzler,Martin Heimann,Ernst-Detlef Schulze,Susan Crow

doi:10.5194/egusphere-egu2020-5062

Carlos Sierra, Holger Metzler + Show 3 more

Open Access

https://doi.org/10.5194/egusphere-egu2020-5062

Copy DOI

Abstract

&lt;p&gt;Ecosystems play a fundamental role in climate change mitigation by taking up carbon from the atmosphere and storing it for a period of time in organic matter. Although climate impacts of carbon emissions can be quantified by global warming potentials, there is not a formal metric to assess climate benefits of carbon removals by sinks. We introduce here the Climate Benefit of Sequestration (CBS), a metric that quantifies the radiative effect of taking up carbon dioxide from the atmosphere and retaining it for a period of time in an ecosystem before releasing it back to the atmosphere. &amp;#160;To quantify CBS, we also propose a formal definition of carbon sequestration (CS) as the integral of a sequestered amount of carbon over the time horizon it remains stored in an ecosystem. Both metrics incorporate the separate effects of i) inputs (amount of atmospheric carbon removal), and ii) transit time (time of carbon retention) in carbon sinks, which can vary largely for different ecosystems or management types. In three separate examples, we show how to compare different carbon management practices in forestry and soils using CS and CBS. We believe these metrics can be useful in resolving current controversies about the management of ecosystems for climate change mitigation.&amp;#160;&lt;/p&gt;

Highlights

Terrestrial ecosystems exchange carbon with the atmosphere at globally significant quantities, thereby influencing Earth’s climate and potentially mitigating warming caused by increasing concentrations of CO2 in the atmosphere
During the time carbon is stored in the terrestrial biosphere, it is removed from the radiative forcing effect that occurs in the atmosphere; it is of scientific and policy relevance to understand the timescale of carbon storage in ecosystems, i.e., for how long newly fixed carbon is retained in an ecosystem before it is released back to the atmosphere
The time carbon remains in an ecosystem, encapsulated in the concept of transit time, is critical for climate change mitigation because during this time carbon is removed from radiative effects in the atmosphere

Summary

Introduction

Terrestrial ecosystems exchange carbon with the atmosphere at globally significant quantities, thereby influencing Earth’s climate and potentially mitigating warming caused by increasing concentrations of CO2 in the atmosphere. Carbon fixed during the process of photosynthesis remains stored in the terrestrial biosphere over a range of timescales, from days to millennia – timescales of relevance for affecting the concentration of greenhouse gases in the atmosphere (Archer et al, 2009; IPCC, 2014; Joos et al, 2013). Transit time characterizes the time that it takes element masses to traverse the entire system, from the time of entry until they are released back to the external environment (Sierra et al, 2017). Both metrics are excellent system-level diagnostics of the dynamics and timescales of ecosystem processes. Because system age and transit time both can be reported as mass or probability distributions, they provide different information about an ecosystem over a wide range in the time domain

Objectives

Findings

Discussion

Conclusion