Future vegetation–climate interactions in Eastern Siberia: an assessment of the competing effects of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and secondary organic aerosols

Almut Arneth,Paul A Miller,Guy Schurgers,Markku Kulmala,Pauli Paasonen,Trofim Maximov,Maija K Kajos,Risto Makkonen,Stefan Olin,Thomas Holst

doi:10.5194/acp-16-5243-2016

Abstract

Abstract. Disproportional warming in the northern high latitudes and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur when increasing temperatures lead, for example, to a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOCs) have been shown to contribute to the growth of secondary organic aerosol (SOA), which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions, and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC–SOA interactions and discuss these changes in terms of possible climate effects. Globally, the effects of changes in Siberian ecosystem CO2 balance and SOA formation are small, but when concentrating on Siberia and the Northern Hemisphere the negative forcing from changed aerosol direct and indirect effects become notable – even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC–SOA interplay serves as an example for the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial processes and highlights the importance of addressing ecosystem–climate feedbacks in consistent, process-based model frameworks.

Highlights

Warming effects on ecosystem carbon cycling in northern ecosystems (Serreze et al, 2000; Tarnocai et al, 2009) and the potential for large climate feedbacks from losses of CO2 or CH4 from these carbon-dense systems have been widely discussed (Khvorostyanov et al, 2008; Schuur et al, 2009; Arneth et al, 2010)
While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and biogenic volatile organic compounds (BVOCs)–secondary organic aerosol (SOA) interplay serves as an example for the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial processes and highlights the importance of addressing ecosystem–climate feedbacks in consistent, process-based model frameworks
Maximum leaf area index (LAI) calculated by the model for the Spasskaya Pad forest (62◦15 18.4 N, 129◦37 07.9 E; 220 m a.s.l.), where the BVOC measurements were obtained, was 2.0 and is in good agreement with the measured values during that period (1.6; Takeshi et al, 2008)

Summary

Introduction

Warming effects on ecosystem carbon cycling in northern ecosystems (Serreze et al, 2000; Tarnocai et al, 2009) and the potential for large climate feedbacks from losses of CO2 or CH4 from these carbon-dense systems have been widely discussed (Khvorostyanov et al, 2008; Schuur et al, 2009; Arneth et al, 2010). Other biogeochemical processes can lead to feedbacks, in particular through emissions of biogenic volatile organic compounds (BVOCs) that are important precursors for tropospheric O3 formation, affect methane lifetime, and act as precursors for secondary organic aerosol (SOA). These latter interactions with SOA have a cooling effect (Arneth et al, 2010; Makkonen et al, 2012b; Paasonen et al, 2013). For present-day conditions, Spracklen et al (2008a) estimated a radiative cooling of −1.8 to −6.7 W per m−2 of boreal forest area from the BVOC– SOA interplay

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