Climate stabilisation under net-zero CO2 emissions at different global warming levels

Global temperature will likely continue to increase until at least mid-century under all emissions scenarios considered. If we want to limit global warming to well below 2 °C, in line with the Paris Agreement, we must achieve net-zero emissions and major economies are targeting net-zero emissions by 2050. However, reaching net-zero emissions will require major changes including carbon dioxide removal (CDR) and we are a long way off achieving this. A delay in emission reductions or the utilization of CDR technologies will lead to at least temporarily exceeding Paris agreement temperature targets. We therefore need to gain a better understanding of the impacts of climate stabilisation at certain temperature levels and the implications of exceeding Paris agreement targets.

In this study we analyse millennium-length simulations from the Australian Earth System Model, ACCESS-ESM1.5, under net-zero CO2 emissions at different global warming levels ranging from about 1.5 °C to 3 °C. Although, the global climate stabilises at those warming levels, the regional climate continues to evolve with significant changes in temperature and rainfall patterns over many centuries including a continued warming over the Southern Ocean and a decline in Antarctic sea-ice. Atmospheric CO2 concentrations continue to decline over most of the 1000 year-long simulation time, mainly due to a continued uptake of carbon by the oceans. However, the land transitions from a carbon sink to a small source long term. Overall, our findings suggest that even under net-zero CO2 emissions long-term (regional) changes in the climate system and carbon cycle are possible.