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Radiative climate feedbacks in the Arctic have been extensively studied, but their spatial and seasonal variations have not been thoroughly examined. Using ERA5 reanalysis data, we examine seasonal variations in Arctic climate feedbacks and their relationship to sea‐ice loss based on changes from 1950–1979 to 1990–2019. The spring and summer seasons experienced large sea‐ice loss, strong surface albedo feedback, and large oceanic heat uptake. Arctic clouds exerted small net cooling in May‐June‐July but moderate warming during the cold season, especially over areas with large sea‐ice loss where cloud liquid and ice water content increased. Arctic water vapor feedback peaked in summer but was weak and uncorrelated with sea‐ice loss. Arctic positive lapse rate feedback (LRF) was strongest in winter over areas with large sea‐ice loss and weak inversion but uncorrelated with atmospheric stability, suggesting that oceanic heating from sea‐ice loss led to enhanced surface warming and the positive LRF.

Many mountain regions around the world are exposed to enhanced warming when compared to their surroundings, threatening key environmental services provided by mountains. Here we investigate this effect, known as elevation-dependent warming (EDW), in the Andes of Ecuador, using observations and simulations with the Weather Research and Forecasting (WRF) Model. EDW is discernible in observations of mean and maximum temperature in the Andes of Ecuador, but large uncertainties remain due to considerable data gaps in both space and time. WRF simulations of present-day (1986–2005) and future climate (RCP4.5 and RCP8.5 for 2041–60) reveal a very distinct EDW signal, with different rates of warming on the eastern and western slopes. This EDW effect is the combined result of multiple feedback mechanisms that operate on different spatial scales. Enhanced upper-tropospheric warming projects onto surface temperature on both sides of the Andes. In addition, changes in the zonal mean midtropospheric circulation lead to enhanced subsidence and warming over the western slopes at high elevation. The increased subsidence also induces drying, reduces cloudiness, and results in enhanced net surface radiation receipts, further contributing to stronger warming. Finally, the highest elevations are also affected by the snow-albedo feedback, due to significant reductions in snow cover by the middle of the twenty-first century. While these feedbacks are more pronounced in the high-emission scenario RCP8.5, our results indicate that high elevations in Ecuador will continue to warm at enhanced rates in the twenty-first century, regardless of emission scenario.

Winter surface air temperature (Tas) over the Barents–Kara Seas (BKS) and other Arctic regions has experienced rapid warming since the late 1990s that has been linked to the concurring cooling over Eurasia, and these multidecadal trends are attributed partly to internal variability. However, how such variability is generated is unclear. Through analyses of observations and model simulations, we show that sea ice–air two-way interactions amplify multidecadal variability in sea-ice cover, sea surface temperatures (SST) and Tas from the North Atlantic to BKS, and the Atlantic Meridional Overturning Circulation (AMOC) mainly through variations in surface fluxes. When sea ice is fixed in flux calculations, multidecadal variations are reduced substantially (by 20–50%) not only in Arctic Tas, but also in North Atlantic SST and AMOC. The results suggest that sea ice–air interactions are crucial for multidecadal climate variability in both the Arctic and North Atlantic, similar to air-sea interactions for tropical climate.

On decadal time scales, Indian Ocean sea surface temperatures (SSTs) exhibit coherent basin‐wide changes, but their origins are not well understood. Here we analyze observations and model simulations from Coupled Model Intercomparison Project Phase 6 and Community Earth System Model Version 1 to quantify the roles of external forcing and internal climate variability in causing Indian Ocean decadal SST variations. Results show that both external forcing and internal variability since 1920 have contributed to the observed decadal variations in linearly detrended Indian Ocean SSTs, and they exhibit an out‐of‐phase relationship since the 1950s. The internally‐generated variations arise from remote influences from the tropical Pacific and possible contributions from internal local processes, while the influence from the Atlantic Multidecadal Oscillation is opposite to that of the Interdecadal Pacific Oscillation. Decadal SST changes caused by nonlinear variations in greenhouse gases and aerosols are roughly out‐of‐phase with the internal variability, thus dampening observed SST variations since the 1950s.

Austral summer precipitation increased by 27% from 1902 to 2020 over southeastern South America (SESA), one of the largest centennial precipitation trends observed globally. We assess the influence of the South American low‐level jet on the SESA precipitation trend by analyzing low‐level moisture fluxes into SESA in two reanalysis datasets from 1951 to 2020. Increased moisture flux through the jet accounts for 20%–45% of the observed SESA precipitation trend. While results vary among reanalyzes, both point to increased humidity as a fundamental driver of increased moisture flux and SESA precipitation. Increased humidity within the jet is consistent with warming sea surface temperatures driven by anthropogenic forcing, although additional natural climate variations also may have played a role. The jet's velocity also increased, further enhancing precipitation, but without a clear connection to anthropogenic forcing. Our findings indicate the SESA precipitation trend is partly attributable to jet intensification arising from both natural variability and anthropogenic forcing.

Recent summer surface air temperature (SAT) variations over Central East Asia (CEA) have been influenced by greenhouse gas and aerosol forcing since 1960. But how CEA SAT responds to contrasting changes in Asian, and European and North American aerosol sources remains unclear. By analyzing observations and model simulations, here we show that aerosol‐forced summer SAT changes over CEA since 1960 come mostly from the effects of aerosols outside Asia, with relatively small influences from Asian aerosols. Unlike Europe, where direct and indirect aerosol effects on surface solar radiation drive the SAT long‐term trend and decadal variations, over CEA atmospheric circulation response to aerosols outside Asia plays an important role. Aerosol‐forced anomalous low‐level low pressure in mid‐latitude Eurasia may influence the SAT anomalies downstream over mid‐latitude Asia, including a warm anomaly around CEA. The results suggest that caution is needed in attributing SAT changes around CEA to anthropogenic aerosols from Asia.

The history of the Polynesian civilization on Rapa Nui (Easter Island) over the Common Era has come to exemplify the fragile relationship humans have with their environment. Social dynamics, deforestation, land degradation, and climatic shifts have all been proposed as important parts of the settlement history and societal transformations on Rapa Nui. Furthermore, climate dynamics of the Southeast Pacific have major global implications. While the wetlands of Rapa Nui contain critical sedimentological archives for reconstructing past hydrological change on the island, connections between the island’s hydroclimate and fundamental aspects of regional climatology are poorly understood. Here we present a hydroclimatology of Rapa Nui showing that there is a clear seasonal cycle of precipitation, with wet months receiving almost twice as much precipitation as dry months. This seasonal cycle can be explained by the seasonal shifts in the location and strength of the climatological south Pacific subtropical anticyclone. For interannual precipitation variability, we find that the occurrence of infrequent, large rain events explains 92% of the variance of the observed annual mean precipitation time series. Approximately one third (33%) of these events are associated with atmospheric rivers, 21% are associated with classic cold-front synoptic systems, and the remainder are characterized by cut-off lows and other synoptic-scale storm systems. As a group, these large rain events are most strongly controlled by the longitudinal position of the south Pacific subtropical anticyclone. The longitudinal location of this anticyclone explains 21% of the variance in the frequency of large rain events, while the remaining variance is left unexplained by any other major atmosphere-ocean dynamics. We find that over the observational era there appears to be no linear relationship between the number of large rain events and any other major climate phenomena. With the south Pacific subtropical anticyclone projected to strengthen and expand westward under global warming, our results imply that Rapa Nui will experience an increase in the number of dry years in the future.

Sea‐ice loss and radiative feedbacks have been proposed to explain Arctic amplification (AA)—the enhanced Arctic warming under increased greenhouse gases, but their relationship is unclear. By analyzing coupled CESM1 simulations with 1%/year CO₂increases, we show that without large sea‐ice loss and AA, the lapse rate, Planck, and surface albedo feedbacks are greatly reduced, while the positive water vapor feedback changes little. The positive Arctic lapse rate feedback, which results from enhanced surface warming rather than the high stability of Arctic air, and changes in atmospheric energy transport across the Arctic Circle are a result, not a cause, of AA; while the water vapor feedback also plays a minor role. Instead, AA results from enhanced winter oceanic heating associated with sea‐ice loss that is aided by a positive surface albedo feedback in summer and positive cloud feedback in winter.

Overestimation of precipitation frequency and duration while underestimating intensity, that is, the “drizzling” bias, has been a long‐standing problem of global climate models. Here we explore this issue from the perspective of precipitation partitioning. We found that most models in the Climate Model Intercomparison Project Phase 5 (CMIP5) have high convective‐to‐total precipitation (PC/PR) ratios in low latitudes. Convective precipitation has higher frequency and longer duration but lower intensity than non‐convective precipitation in many models. As a result, the high PC/PR ratio contributes to the “drizzling” bias over low latitudes. The PC/PR ratio and associated “drizzling” bias increase as model resolution coarsens from 0.5° to 2.0°, but the resolution's effect weakens as the grid spacing increases from 2.0° to 3.0°. Some of the CMIP6 models show reduced “drizzling” bias associated with decreased PC/PR ratio. Thus, more reasonable precipitation partitioning, along with finer model resolution should alleviate the “drizzling” bias within current climate models.