On the causes of trends in the seasonal amplitude of atmospheric CO₂

Abstract

No consensus has yet been reached on the major factors driving the observed increase in the seasonal amplitude of atmospheric CO in the northern latitudes. In this study, we used atmospheric CO records from 26 northern hemisphere stations with a temporal coverage longer than 15 years, and an atmospheric transport model prescribed with net biome productivity (NBP) from an ensemble of nine terrestrial ecosystem models, to attribute change in the seasonal amplitude of atmospheric CO . We found significant (p < .05) increases in seasonal peak-to-trough CO amplitude (AMP ) at nine stations, and in trough-to-peak amplitude (AMP ) at eight stations over the last three decades. Most of the stations that recorded increasing amplitudes are in Arctic and boreal regions (>50°N), consistent with previous observations that the amplitude increased faster at Barrow (Arctic) than at Mauna Loa (subtropics). The multi-model ensemble mean (MMEM) shows that the response of ecosystem carbon cycling to rising CO concentration (eCO ) and climate change are dominant drivers of the increase in AMP and AMP in the high latitudes. At the Barrow station, the observed increase of AMP and AMP over the last 33 years is explained by eCO (39% and 42%) almost equally than by climate change (32% and 35%). The increased carbon losses during the months with a net carbon release in response to eCO are associated with higher ecosystem respiration due to the increase in carbon storage caused by eCO during carbon uptake period. Air-sea CO fluxes (10% for AMP and 11% for AMP ) and the impacts of land-use change (marginally significant 3% for AMP and 4% for AMP ) also contributed to the CO measured at Barrow, highlighting the role of these factors in regulating seasonal changes in the global carbon cycle.

Higher than expected CO2 fertilization inferred from leaf to global observations

“…Bastos et al (2019) identify Eurasia as the region contributing most to increasing seasonal amplitude of CO 2 -a region that is dominated by natural ecosystems and has experienced very little land use change (Verburg et al, 2015) over the last half-century. A limitation of the study by Piao et al (2017) is that it relies on an ensemble of models, many of which do not account for agricultural intensification. Bastos et al…”

Changes in the Response of the Northern Hemisphere Carbon Uptake to Temperature Over the Last Three Decades

“…The longest record is from the Barrow station, covering the period from 1973 to 2015 after excluding discontinuous sampling in the late 1960s. CO 2 signals detected at Barrow are influenced by carbon fluxes from both the high latitudes and the midlatitudes through atmospheric transport and mixing (Liu, Wang, Ciais, et al, ). Previous studies suggested that the major contribution to the CO 2 seasonal cycle is from boreal (~35%) and arctic (~35%) ecosystems, while the temperate and the subtropical regions contribute ~30% (Graven et al, ).…”

“…The seasonal cycle amplitude (SCA) of atmospheric CO 2 —an integrated signal of the terrestrial ecosystem metabolism—has increased since the 1960s (Keeling et al, ), most significantly in regions north of 45°N where an increase of 50% has occurred at altitudes of 3 to 6 km over the last 50 years (Graven et al, ). Many studies have analyzed the drivers of this SCA increase and identified factors associated with enhanced photosynthetic uptake in the midlatitude and high latitude, for example, climate warming, a lengthening growing season, CO 2 fertilization, and nitrogen deposition (Forkel et al, ; Graven et al, ; Keeling et al, ; Randerson et al, ; Zhu et al, ), while a fraction of this enhanced uptake is released back to the atmosphere during the nongrowing season (Piao et al, ; Piao, Liu, Wang, Ciais, et al, ).…”

The influence of rising tropospheric carbon dioxide and ozone on plant productivity

“…; Piao et al . ). By compiling data from inventory, simulation and atmospheric studies, Schimel et al .…”