Evaluation of external drivers on Arctic warming in the early 20th century based on climate simulations using MRI-ESM2.0 and multi-model analysis

Abstract:

Instrumental records show that there was a significant warming in the Arctic in the first half of the twentieth Century, known as the early twentieth century warming (ETCW). The degrees of the response to external climate forcing on this temperature variation still have not been well understood. In this study, climate simulations using a state-of-the-art climate model of Meteorological Research Institute (MRI-ESM2.0) and multi-model analyses using 12 state-of-the-art climate models were conducted to quantitatively understand the ETCW. Results of this detection and attribution experiments suggest that a long-term low volcanic activity was one of major factors on the model-simulated ETCW. The MRI-ESM2.0 simulation also indicates that the sea-ice extent likely decreased in response to the Arctic warming. Both the climate simulations of MRI-ESM2.0 and the multi-model analyses indicate that the rates of change in simulated Arctic temperature for 30 years from 1911 to 1940 due to responses to the external natural forcing are 1.1-1.2 times larger than the multi-decadal internal variability of models. Meanwhile, the response to increasing greenhouse gases in the period of ETCW from 1911 to 1940 was very weak, or canceled out by the effect of anthropogenic aerosols increase.