Carbon neutrality and mitigating contribution of terrestrial carbon sink on anthropogenic climate warming in China, the United States, Russia and Canada

Carbon dioxide (CO2) is a major climate forcing factor, closely related to human activities. Quantifying the contribution of CO2 emissions to the global radiative forcing (RF) is therefore important to evaluate climate effects caused by anthropogenic and natural factors. China, the United States (USA), Russia and Canada are the largest countries by land area, at different levels of socio-economic development. In this study, we used data from the CarbonTracker CO2 assimilation model (CT2017 data set) to analyze anthropogenic CO2 emissions and terrestrial ecosystem carbon sinks from 2000 to 2016. We derived net RF contributions and showed that anthropogenic CO2 emissions had increased significantly from 2000 to 2016, at a rate of 0.125 PgC yr−1. Over the same period, carbon uptake by terrestrial ecosystems increased at a rate of 0.003 PgC yr−1. Anthropogenic CO2 emissions in China and USA accounted for 87.19% of the total, while Russian terrestrial ecosystems were the largest carbon sink and absorbed 14.69 PgC. The resulting cooling effect was −0.013 W m−2 in 2016, representing an offset of −45.06% on climate warming induced by anthropogenic CO2. This indicates that net climate warming would be significantly overestimated if terrestrial ecosystems were not included in RF budget analyses. In terms of cumulative effects, we analyzed RFs using reference atmospheres of 1750, at the start of the Industrial Revolution, and 2000, the initial year of this study. Anthropogenic CO2 emissions in the study area contributed by + 0.42 W m−2 and +0.32 W m−2 to the global RF, relative to CO2 levels of 1750 and 2000, respectively. We also evaluated correlations between global mean atmospheric temperature and net, anthropogenic and natural RFs. We found that the combined (net) RF caused by CO2 emissions accounted for 30.3% of global mean temperature variations in 2000–2016.