Abstract:In 2015, by signing up to the Paris Agreement on climate change, the United Nations Framework Convention on Climate Change (UNFCCC) parties pledged to keep global temperatures "well below" 2℃ above pre-industrial levels and to "pursue efforts to limit the temperature increase even further to 1.5℃". Limiting warming to 1.5℃/2℃ requires strictly limiting the total amount of carbon emissions between now and the end of the century. Global mean surface temperature has already witnessed a 1℃ more warming since the pre-industrial era and the cumulative anthropogenic CO₂ emission has reached around 2 390 Gt CO₂. An accurate estimation of the allowable amount of additional carbon emissions, known as the "remaining carbon budget", is crucial to climate change mitigation activities. In this study, we hope to provide a commentary on improving the quality and reducing the uncertainty in remaining carbon budget estimation. After a brief review on the relationship between carbon cycle and global warming, we introduce the methods for estimating the remaining carbon budget and compare the results presented in a series of assessment reports since IPCC AR5 and IPCC AR6. The reasons for the different estimations of remaining carbon budget presented in the reports are discussed. Finally, the priorities of future research fields/directions toward an accurate estimation of remaining carbon budget are proposed.