Emerging negative impact of warming on summer carbon uptake in northern ecosystems

Tao Wang,Yongwen Liu,Yi Yin,Ivan Janssens,Yitong Yao,Shushi Peng,Mengtian Huang,Hui Guo,Philippe Ciais,Josep Peñuelas,Xu Lian,Yutong Zhao,Yilong Wang,Shilong Piao,Xiaoyi Wang,John F Burkhart,Yue Li,Hui Yang,Dan Liu

doi:10.1038/s41467-018-07813-7

Abstract

Most studies of the northern hemisphere carbon cycle based on atmospheric CO2 concentration have focused on spring and autumn, but the climate change impact on summer carbon cycle remains unclear. Here we used atmospheric CO2 record from Point Barrow (Alaska) to show that summer CO2 drawdown between July and August, a proxy of summer carbon uptake, is significantly negatively correlated with terrestrial temperature north of 50°N interannually during 1979–2012. However, a refined analysis at the decadal scale reveals strong differences between the earlier (1979–1995) and later (1996–2012) periods, with the significant negative correlation only in the later period. This emerging negative temperature response is due to the disappearance of the positive temperature response of summer vegetation activities that prevailed in the earlier period. Our finding, together with the reported weakening temperature control on spring carbon uptake, suggests a diminished positive effect of warming on high-latitude carbon uptake.

Highlights

Most studies of the northern hemisphere carbon cycle based on atmospheric CO2 concentration have focused on spring and autumn, but the climate change impact on summer carbon cycle remains unclear
summer CO2 drawdown (SCD) was not significantly correlated with summer temperature in the previous 2 years for any of the study periods (1979–2012, or the two periods 1979–1995 and 1996–2012). This lack of lagged-correlation coincides with a non-significant lagged-response of summer productivity to temperature in the previous one or 2 years (Supplementary Fig. 3). This result does not contradict the result from Keeling et al.[30], but it shows that if there is a lagged response of the peak-to-peak CO2 amplitude to temperature, it is not due to a lag of summer CO2 uptake
We found that Normalized Difference Vegetation Index (NDVI) and temperature across ecosystems north of 50°N were always significantly positively correlated during the earlier period (R = 0.82 ± 0.07), but not the later period (R = 0.08 ± 0.19) (Fig. 2a), supporting this hypothesis

Summary

Introduction

Most studies of the northern hemisphere carbon cycle based on atmospheric CO2 concentration have focused on spring and autumn, but the climate change impact on summer carbon cycle remains unclear. With simultaneous use of multiple satellitederived products[26,27,28], an ensemble of terrestrial carbon cycle models and simulations with an atmospheric transport model[29] (Methods), we show that there is a significant-negative interannual correlation between SCD with summer land temperature north of 50°N during 1979–2012, and such significant negative correlation only occurred during the earlier period (1979–1995) instead of during the later period (1996–2012). This emergentnegative relationship is primarily due to summer vegetation activities no longer positively responding to temperature

Objectives

Methods

Results

Conclusion