Ocean fronts as decadal thermostats modulating continental warming hiatus.

Over the past decade, an unexpected cooling trend has been observed in East Asia and North America during winter. Climate model simulations suggest that this pattern of stalled warming, besides accelerated warming, will repeat throughout the course of global warming, influenced by the natural decade-long variations in the climate system. However, understanding the exact factors affecting the pace of warming remains a challenge. Here we show that a pause in warming over continental areas-namely, local warming hiatus-can be accompanied by excessive heat accumulation north of the ocean fronts. This oceanic condition, often manifesting in the form of marine heatwaves, constrains the subseasonal growth of atmospheric planetary waves, significantly increasing the likelihood of cold extremes in downstream continents. Our results underscore the importance of closely monitoring changing ocean fronts in response to human-induced warming, which can potentially reshape the inherent decade-long fluctuations within regional climates over the long term.

Hysteresis of the El Niño-Southern Oscillation to CO2 forcing.

El Niño-Southern Oscillation (ENSO) is the strongest interannual climate variability with far-reaching socioeconomic consequences. Many studies have investigated ENSO-projected changes under future greenhouse warming, but its responses to plausible mitigation behaviors remain unknown. We show that ENSO sea surface temperature (SST) variability and associated global teleconnection patterns exhibit strong hysteretic responses to carbon dioxide (CO2) reduction based on the 28-member ensemble simulations of the CESM1.2 model under an idealized CO2 ramp-up and ramp-down scenario. There is a substantial increase in the ensemble-averaged eastern Pacific SST anomaly variance during the ramp-down period compared to the ramp-up period. Such ENSO hysteresis is mainly attributed to the hysteretic response of the tropical Pacific Intertropical Convergence Zone meridional position to CO2 removal and is further supported by several selected single-member Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulations. The presence of ENSO hysteresis leads to its amplified and prolonged impact in a warming climate, depending on the details of future mitigation pathways.

Hemispherically asymmetric Hadley cell response to CO2 removal.

A poleward shift of the Hadley cell (HC) edge in a warming climate, which contributes to the expansion of drought-prone subtropical regions, has been widely documented. The question addressed here is whether this shift is reversible with CO2 removal. By conducting large-ensemble experiments where CO2 concentrations are systematically increased and then decreased to the present-day level, we show that the poleward-shifted HC edge in a warming climate does not return to its present-day state when CO2 concentrations are reduced. While the Southern Hemisphere HC edge remains poleward of its present-day state, the Northern Hemisphere HC edge ends up farther equatorward of its present-day state. Such hemispherically asymmetric HC edge changes are closely associated with the changes in vertical wind shear in the subtropical atmosphere, which result from the long adjustment time of the ocean response to CO2 removal. Our findings suggest that CO2 removal may not guarantee the recovery of the subtropical dryness associated with the HC changes.

Increase in convective extreme El Niño events in a CO2 removal scenario.

Convective extreme El Niño (CEE) events, characterized by strong convective events in the eastern Pacific, are known to have a direct link to anomalous climate conditions worldwide, and it has been reported that CEE will occur more frequently under greenhouse warming. Here, using a set of CO2 ramp-up and ramp-down ensemble experiments, we show that frequency and maximum intensity of CEE events increase further in the ramp-down period from the ramp-up period. These changes in CEE are associated with the southward shift of the intertropical convergence zone and intensified nonlinear rainfall response to sea surface temperature change in the ramp-down period. The increasing frequency of CEE has substantial impacts on regional abnormal events and contributed considerably to regional mean climate changes to the CO2 forcings.

Asymmetrical response of summer rainfall in East Asia to CO2 forcing.

Understanding the regional hydrological response to varying CO2 concentration is critical for cost-benefit analysis of mitigation and adaptation polices in the near future. To characterize summer monsoon rainfall change in East Asia in a changing CO2 pathway, we used the Community Earth System Model (CESM) with 28 ensemble members in which the CO2 concentration increases at a rate of 1% per year until its quadrupling peak, i.e., 1468 ppm (ramp-up period), followed by a decrease of 1% per year until the present-day climate conditions, i.e., 367 ppm (ramp-down period). Although the CO2 concentration change is symmetric in time, the amount of summer rainfall anomaly in East Asia is increased 42% during a ramp-down period than that during a ramp-up period when the two periods of the same CO2 concentration are compared. This asymmetrical rainfall response is mainly due to an enhanced El Niño-like warming pattern as well as its associated increase in the sea surface temperature in the western North Pacific during a ramp-down period. These sea surface temperature patterns enhance the atmospheric teleconnections and the local meridional circulations around East Asia, resulting in more rainfall over East Asia during a ramp-down period. This result implies that the removal of CO2 does not guarantee the return of regional rainfall to the previous climate state with the same CO2 concentration.

General circulation and global heat transport in a quadrupling CO2 pulse experiment.

To investigate the response of the general circulation and global transport of heat through both atmosphere and ocean to two-types of carbon dioxide removal scenario, we performed an earth system model experiment in which we imposed a pulse-type quadrupling of CO2 forcing for 50 years and a gradual peak-and-decline of four-time CO2 forcing. We found that the results from two experiments are qualitatively similar to each other. During the forcing-on period, a dominant warming in the upper troposphere over the tropics and on the surface at high latitudes led to a slowdown in the Hadley circulation, but the poleward atmospheric energy transport was enhanced due to an increase in specific humidity. This counteracted the reduction in poleward oceanic energy transport owing to the suppression of the meridional overturning circulation in both Hemispheres. After returning the original CO2 level, the hemispheric thermal contrast was reversed, causing a southward shift of the intertropical convergence zone. To reduce the hemispheric thermal contrast, the northward energy transports in the atmosphere and ocean surface were enhanced while further weakening of the global-scale Atlantic meridional overturning circulation led to southward energy transport in the deep ocean.

Transcatheter Arterial Embolization for Gastrointestinal Bleeding Secondary to Gastrointestinal Lymphoma.

PURPOSE: To evaluate the effectiveness of transcatheter arterial embolization (TAE) for gastrointestinal (GI) bleeding caused by GI lymphoma. MATERIALS AND METHODS: The medical records of 11 patients who underwent TAE for GI bleeding caused by GI lymphoma between 2001 and 2015 were reviewed retrospectively. RESULTS: A total of 20 TAE procedures were performed. On angiography, contrast extravasation, and both contrast extravasation and tumor staining were seen in 95 % (19/20) and 5 % (1/20) of the procedures, respectively. The most frequently embolized arteries were jejunal (n = 13) and ileal (n = 5) branches. Technical and clinical success rates were 100 % (20/20) and 27 % (3/11), respectively. The causes of clinical failure in eight patients were rebleeding at new sites. In four patients who underwent repeat angiography, the bleeding focus was new each time. Three patients underwent small bowel resection due to rebleeding after one (n = 2) or four (n = 1) times of TAEs. Another two patients underwent small bowel resection due to small bowel ischemia/perforation after three or four times of TAEs. The 30-day mortality rate was 18 % due to hypovolemic shock (n = 1) and multiorgan failure (n = 1). CONCLUSION: Angiogram with TAE shows limited therapeutic efficacy to manage GI lymphoma-related bleeding due to high rebleeding at new sites. Although TAE can be an initial hemostatic measure, surgery should be considered for rebleeding due to possible bowel ischemic complication after repeated TAE procedures.