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Arctic hydrological cycle has important global implications through modifying deep ocean circulation via fresh water fluxes. However, attribution of the observed changes in Arctic moisture budget remains challenging due to the lack of reliable observations. Here, as a first step, past changes in hydrological cycle over the Arctic were evaluated using CMIP6 historical simulations. To examine possible influences of individual external forcings, CMIP6 multi-model simulations performed under natural-plus-anthropogenic (ALL), greenhouse gas (GHG), natural (NAT), and aerosol (AER) forcings were compared. Results indicate that Arctic precipitation and evaporation increase in ALL and GHG but decrease in AER. In ALL and GHG, Arctic precipitation increases in summer mainly due to enhanced poleward moisture transport whereas Arctic moistening during winter is affected more by increased surface evaporation over sea-ice retreat areas. In AER, Arctic precipitation tends to decrease due to reduced evaporation over sea-ice advance areas during cold months. Poleward meridional moisture flux (MMF) across 70°N is the strongest in summer due to the highest moisture. GHG has stronger MMF than other forcing simulations due to larger increase in moisture in line with stronger warming. The MMF response is found to be largely determined by variations in transient eddies with distinct seasonal and regional contributions. [ABSTRACT FROM AUTHOR]

Using a statistical method, we examined the time of emergence (ToE), which was defined as the year when the global mean surface temperature (GMST) trend exceeds the trend explained by internal variability, using 33 Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models for 1861–2100. We found that the GMST trend explained by internal variability showed minimal changes even though the GMST trend rapidly increased under the Representative Climate Pathway 8.5 scenario. However, there was large intermodel diversity for the ToEs in CMIP5 climate models. The intensity of Arctic amplification was closely associated with intermodel diversity of the ToEs. A significant difference in the amount of Arctic sea ice extent during the reference period (1861‐1910) played a role in determining whether there was slow or fast simulation of the ToE in CMIP5 climate models. We argue that a slow or fast ToE is influenced by how the climate models initially simulate the sea ice extent during the reference period. Plain Language Summary: In our society, it is quite important to know the time of emergence (ToE), which is typically defined as the notion that a new climate state can be said to have emerged when it deviates significantly from a prior reference period, to correctly build up an adaptation and mitigation strategy in a changing climate. Although we did not use a typical definition of ToE, we found that the ToEs simulated in climate models are quite diverse. We found the intensity of Arctic amplification was closely associated with intermodel diversity of the ToEs. Our further analysis indicated that the amount of sea ice extent in the Arctic during the reference period may influence the ToEs in climate model. Therefore, it is quite important to correctly simulate the Arctic sea ice extent to correctly project the ToEs in a changing climate. Key Points: We define the time of emergence as the year when the GMST trend exceeds the trend explained by IV in climate modelsThe diversity of GMST in CMIP5 climate models after the mid‐21st century could be mainly attributed to the model's characteristicsThe sea ice extent during the reference period plays a key role in determining the ToE in CMIP5 climate models [ABSTRACT FROM AUTHOR]

Little attention has been paid to the influence of Arctic sea ice loss on climate variability in the tropical Pacific. By analyzing observational data sets, we hypothesized that anomalous Arctic sea ice concentration variations have the potential to influence tropical Pacific sea surface temperature (SST) variability via atmosphere‐ocean coupled processes in the eastern subtropical North Pacific. To test this hypothesis, we conducted idealized model experiments with 15 ensembles in which historical SSTs for 1951–2016 were restored in the Arctic only with different initial conditions. We found that a positive phase of North Pacific Oscillation‐like atmospheric circulation, which is modulated by a sea ice reduction in the Pacific Arctic sector, triggers El Niño‐like warming in the central tropical Pacific. This implies that connections between the Arctic and the tropics should be considered for further understanding of changes in El Niño and other tropical Pacific climate variability in a changing climate. Key Points: Arctic sea ice concentration variations have the potential to influence tropical Pacific sea surface temperatureA North Pacific Oscillation‐like atmospheric circulation triggers El Niño‐like warming in the central tropical Pacific through a SFMConnections between the Arctic and the tropics should be considered for further understanding of changes in ENSO in a warmer world [ABSTRACT FROM AUTHOR]