Non-uniform seasonal warming regulates vegetation greening and atmospheric CO2 amplification over northern lands

Zhao Li,Shushi Peng,Anders Ahlström,Junyi Liang,Jianyang Xia,Zheng Shi,Wanying Cheng,Lifen Jiang,Jinwei Dong,Guangsheng Chen,Liming Yan,Philippe Ciais,D J Hayes ,Duoying Ji,John C Moore ,A D Mcguire ,Geli Zhang,Xiangming Xiao,Gerhard Krinner,Annette Rinke,Ying‐Ping Wang ,C Koven ,Yiqi Luo

doi:10.1088/1748-9326/aae9ad

Abstract

The enhanced vegetation growth by climate warming plays a pivotal role in amplifying the seasonal cycle of atmospheric CO2 at northern lands (>50° N) since 1960s. However, the correlation between vegetation growth, temperature and seasonal amplitude of atmospheric CO2 concentration have become elusive with the slowed increasing trend of vegetation growth and weakened temperature control on CO2 uptake since late 1990s. Here, based on in situ atmospheric CO2 concentration records from the Barrow observatory site, we found a slowdown in the increasing trend of the atmospheric CO2 amplitude from 1990s to mid-2000s. This phenomenon was associated with the paused decrease in the minimum CO2 concentration ([CO2]min), which was significantly correlated with the slowdown of vegetation greening and growing-season length extension. We then showed that both the vegetation greenness and growing-season length were positively correlated with spring but not autumn temperature over the northern lands. Furthermore, such asymmetric dependences of vegetation growth upon spring and autumn temperature cannot be captured by the state-of-art terrestrial biosphere models. These findings indicate that the responses of vegetation growth to spring and autumn warming are asymmetric, and highlight the need of improving autumn phenology in the models for predicting seasonal cycle of atmospheric CO2 concentration.

Highlights

Temporal dynamics of atmospheric CO2 concentration, climate and terrestrial carbon (C) cycle are strongly linked in the present (Schneising et al 2014) and past (Montañez et al 2016) Earth systems
We examined the relationships between temperature and gross primary productivity (GPP) in five terrestrial biosphere models (TBMs), which have been commonly incorporated into Earth system models for future projections of climate and atmospheric changes
The temporal changes of atmospheric CO2 seasonal cycle and vegetation greenness We first examined the trends of the measured annual CO2 amplitude ([CO2]amplitude) at Point BRW, Alaska (71°N)

Summary

Introduction

Temporal dynamics of atmospheric CO2 concentration, climate and terrestrial carbon (C) cycle are strongly linked in the present (Schneising et al 2014) and past (Montañez et al 2016) Earth systems. An increasing amplitude of the atmospheric CO2 seasonal cycle at northern high latitudes has been observed since 1960s (Bacastow et al 1985, Keeling et al 1996, Randerson et al 1997, Graven et al 2013), e.g. about 0.53% yr−1 at the Point Barrow (BRW) during 1971–2011 (Forkel et al 2016). The major contributors to such trend of seasonal atmospheric CO2 amplitude are still in debate (Gray et al 2014, Zeng et al 2014, Ito et al 2016, Wenzel et al 2016, Piao et al 2017a), the associated increases in mean annual temperature (MAT) and vegetation growth has been recognized as one important driver (Forkel et al 2016, Gonsamo et al 2017, Piao et al 2017a, Yuan et al 2018). Given that climate warming in different seasons would influence vegetation growth differently (Xu et al 2013, Xia et al 2014, Cai et al 2016), the role of seasonal non-uniform warming in affecting the vegetation growth as well as the recent changes of the atmospheric CO2 amplitude remains unclear

Methods

Results

Conclusion