Effect of Early vs Late Inguinal Hernia Repair on Serious Adverse Event Rates in Preterm Infants: A Randomized Clinical Trial.

Importance: Inguinal hernia repair in preterm infants is common and is associated with considerable morbidity. Whether the inguinal hernia should be repaired prior to or after discharge from the neonatal intensive care unit is controversial. Objective: To evaluate the safety of early vs late surgical repair for preterm infants with an inguinal hernia. Design, Setting, and Participants: A multicenter randomized clinical trial including preterm infants with inguinal hernia diagnosed during initial hospitalization was conducted between September 2013 and April 2021 at 39 US hospitals. Follow-up was completed on January 3, 2023. Interventions: In the early repair strategy, infants underwent inguinal hernia repair before neonatal intensive care unit discharge. In the late repair strategy, hernia repair was planned after discharge from the neonatal intensive care unit and when the infants were older than 55 weeks' postmenstrual age. Main Outcomes and Measures: The primary outcome was occurrence of any prespecified serious adverse event during the 10-month observation period (determined by a blinded adjudication committee). The secondary outcomes included the total number of days in the hospital during the 10-month observation period. Results: Among the 338 randomized infants (172 in the early repair group and 166 in the late repair group), 320 underwent operative repair (86% were male; 2% were Asian, 30% were Black, 16% were Hispanic, 59% were White, and race and ethnicity were unknown in 9% and 4%, respectively; the mean gestational age at birth was 26.6 weeks [SD, 2.8 weeks]; the mean postnatal age at enrollment was 12 weeks [SD, 5 weeks]). Among 308 infants (91%) with complete data (159 in the early repair group and 149 in the late repair group), 44 (28%) in the early repair group vs 27 (18%) in the late repair group had at least 1 serious adverse event (risk difference, -7.9% [95% credible interval, -16.9% to 0%]; 97% bayesian posterior probability of benefit with late repair). The median number of days in the hospital during the 10-month observation period was 19.0 days (IQR, 9.8 to 35.0 days) in the early repair group vs 16.0 days (IQR, 7.0 to 38.0 days) in the late repair group (82% posterior probability of benefit with late repair). In the prespecified subgroup analyses, the probability that late repair reduced the number of infants with at least 1 serious adverse event was higher in infants with a gestational age younger than 28 weeks and in those with bronchopulmonary dysplasia (99% probability of benefit in each subgroup). Conclusions and Relevance: Among preterm infants with inguinal hernia, the late repair strategy resulted in fewer infants having at least 1 serious adverse event. These findings support delaying inguinal hernia repair until after initial discharge from the neonatal intensive care unit. Trial Registration: ClinicalTrials.gov Identifier: NCT01678638.

Frequency and predictors of complication clustering within 30 days of spinal fusion surgery: a study of children with neuromuscular scoliosis.

PURPOSE: There is limited information on the clustering or co-occurrence of complications after spinal fusion surgery for neuromuscular disease in children. We aimed to identify the frequency and predictive factors of co-occurring perioperative complications in these children. METHODS: In this retrospective database cohort study, we identified children (ages 10-18 years) with neuromuscular scoliosis who underwent elective spinal fusion in 2012-2020 from the National Surgical Quality Improvement Program-Pediatric database. The rates of co-occurring complications within 30 days were calculated, and associated factors were identified by logistic regression analysis. Correlation between a number of complications and outcomes was assessed. RESULTS: Approximately 11% (709/6677 children with neuromuscular scoliosis undergoing spinal fusion had co-occurring complications: 7% experienced two complications and 4% experienced ≥ 3. The most common complication was bleeding/transfusion (80%), which most frequently co-occurred with pneumonia (24%) and reintubation (18%). Surgical time ≥ 400 min (odds ratio (OR) 1.49 [95% confidence interval (CI) 1.25-1.75]), fusion ≥ 13 levels (1.42 [1.13-1.79]), and pelvic fixation (OR 1.21 [1.01, 1.44]) were identified as procedural factors that independently predicted concurrent complications. Clinical risk factors for co-occurring complications included an American Society of Anesthesiologist physical status classification ≥ 3 (1.73 [1.27-2.37]), structural pulmonary/airway abnormalities (1.24 [1.01-1.52]), impaired cognitive status (1.80 [1.41-2.30]), seizure disorder (1.36 [1.12-1.67]), hematologic disorder (1.40 [1.03-1.91], preoperative nutritional support (1.34 [1.08-1.72]), and congenital malformations (1.20 [1.01-1.44]). Preoperative tracheostomy was protective against concurrent complications (0.62 [0.43-0.89]). Significant correlations were found between number of complications and length of stay, non-home discharge, readmissions, and death. CONCLUSION: Longer surgical time (≥ 400 min), fusion ≥ 13 levels and pelvic fixation are surgical risk factors independently associated with co-occurring complications, which were associated with poorer patient outcomes. Recognizing identified nonmodifiable risk factors might also be important for preoperative planning and risk stratification of children with neuromuscular scoliosis requiring spinal fusion. LEVEL OF EVIDENCE: Level IV evidence.

Race Does Not Affect Rates of Surgical Complications at Military Treatment Facility.

INTRODUCTION: Racial minorities have been found to have worse health care outcomes, including perioperative adverse events. We hypothesized that these racial disparities may be mitigated in a military treatment facility, where all patients have a military service connection and are universally insured. MATERIALS AND METHODS: This is a single institution retrospective review of American College of Surgeons National Surgical Quality Improvement Program data for all procedures collected from 2017 to 2020. The primary outcome analyzed was risk-adjusted 30-day postoperative complications compared by race. RESULTS: There were 6,941 patients included. The overall surgical complication rate was 6.9%. The complication rate was 7.3% for White patients, 6.5% for Black patients, 12.6% for Asian patients, and 3.4% for other races. However, after performing patient and procedure level risk adjustment using multivariable logistic regression, race was not independently associated with surgical complications. CONCLUSIONS: Risk-adjusted surgical complication rates do not vary by race at this military treatment facility. This suggests that postoperative racial disparities may be mitigated within a universal health care system.

Frequency and predictors of concurrent complications in multi-suture release for syndromic craniosynostosis.

PURPOSE: Understanding the complication profile of craniosynostosis surgery is important, yet little is known about complication co-occurrence in syndromic children after multi-suture craniosynostosis surgery. We examined concurrent perioperative complications and predictive factors in this population. METHODS: In this retrospective cohort study, children with syndromic diagnoses and multi-suture involvement who underwent craniosynostosis surgery in 2012-2020 were identified from the National Surgical Quality Improvement Program-Pediatric database. The primary outcome was concurrent complications; factors associated with concurrent complications were identified. Correlations between complications and patient outcomes were assessed. RESULTS: Among 5,848 children identified, 161 children (2.75%) had concurrent complications: 129 (2.21%) experienced two complications and 32 (0.55%) experienced ≥ 3. The most frequent complication was bleeding/transfusion (69.53%). The most common concurrent complications were transfusion/superficial infection (27.95%) and transfusion/deep incisional infection (13.04%) or transfusion/sepsis (13.04%). Two cardiac factors (major cardiac risk factors (odds ratio (OR) 3.50 [1.92-6.38]) and previous cardiac surgery (OR 4.87 [2.36-10.04])), two pulmonary factors (preoperative ventilator dependence (OR 3.27 [1.16-9.21]) and structural pulmonary/airway abnormalities (OR 2.89 [2.05-4.08])), and preoperative nutritional support (OR 4.05 [2.34-7.01]) were independently associated with concurrent complications. Children who received blood transfusion had higher odds of deep surgical site infection (OR 4.62 [1.08-19.73]; p = 0.04). CONCLUSIONS: Our results indicate that several cardiac and pulmonary risk factors, along with preoperative nutritional support, were independently associated with concurrent complications but procedural factors were not. This information can help inform presurgical counseling and preoperative risk stratification in this population.

Anthropogenic climate change impacts exacerbate summer forest fires in California.

Record-breaking summer forest fires have become a regular occurrence in California. Observations indicate a fivefold increase in summer burned area (BA) in forests in northern and central California during 1996 to 2021 relative to 1971 to 1995. While the higher temperature and increased dryness have been suggested to be the leading causes of increased BA, the extent to which BA changes are due to natural variability or anthropogenic climate change remains unresolved. Here, we develop a climate-driven model of summer BA evolution in California and combine it with natural-only and historical climate simulations to assess the importance of anthropogenic climate change on increased BA. Our results indicate that nearly all the observed increase in BA is due to anthropogenic climate change as historical model simulations accounting for anthropogenic forcing yield 172% (range 84 to 310%) more area burned than simulations with natural forcing only. We detect the signal of combined historical forcing on the observed BA emerging in 2001 with no detectable influence of the natural forcing alone. In addition, even when considering fuel limitations from fire-fuel feedbacks, a 3 to 52% increase in BA relative to the last decades is expected in the next decades (2031 to 2050), highlighting the need for proactive adaptations.

Evaluation and Management of Primary Spontaneous Pneumothorax in Adolescents and Young Adults: A Systematic Review From the APSA Outcomes & Evidence-Based Practice Committee.

INTRODUCTION: Controversy exists in the optimal management of adolescent and young adult primary spontaneous pneumothorax. The American Pediatric Surgical Association (APSA) Outcomes and Evidence-Based Practice Committee performed a systematic review of the literature to develop evidence-based recommendations. METHODS: Ovid MEDLINE, Elsevier Embase, EBSCOhost CINAHL, Elsevier Scopus, and Wiley Cochrane Central Register of Controlled Trials databases were queried for literature related to spontaneous pneumothorax between January 1, 1990, and December 31, 2020, addressing (1) initial management, (2) advanced imaging, (3) timing of surgery, (4) operative technique, (5) management of contralateral side, and (6) management of recurrence. The Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines were followed. RESULTS: Seventy-nine manuscripts were included. Initial management of adolescent and young adult primary spontaneous pneumothorax should be guided by symptoms and can include observation, aspiration, or tube thoracostomy. There is no evidence of benefit for cross-sectional imaging. Patients with ongoing air leak may benefit from early operative intervention within 24-48 h. A video-assisted thoracoscopic surgery (VATS) approach with stapled blebectomy and pleural procedure should be considered. There is no evidence to support prophylactic management of the contralateral side. Recurrence after VATS can be treated with repeat VATS with intensification of pleural treatment. CONCLUSIONS: The management of adolescent and young adult primary spontaneous pneumothorax is varied. Best practices exist to optimize some aspects of care. Further prospective studies are needed to better determine optimal timing of operative intervention, the most effective operation, and management of recurrence after observation, tube thoracostomy, or operative intervention. LEVEL OF EVIDENCE: Level 4. TYPE OF STUDY: Systematic Review of Level 1-4 studies.

Surgical Management of Ulcerative Colitis in Children and Adolescents: A Systematic Review from the APSA Outcomes and Evidence-Based Practice Committee.

INTRODUCTION: The incidence of ulcerative colitis (UC) is increasing. Roughly 20% of all patients with UC are diagnosed in childhood, and children typically present with more severe disease. Approximately 40% will undergo total colectomy within ten years of diagnosis. The objective of this study is to assess the available evidence regarding the surgical management of pediatric UC as determined by the consensus agreement of the American Pediatric Surgical Association Outcomes and Evidence-Based Practice Committee (APSA OEBP). METHODS: Through an iterative process, the membership of the APSA OEBP developed five a priori questions focused on surgical decision-making for children with UC. Questions focused on surgical timing, reconstruction, use of minimally invasive techniques, need for diversion, and risks to fertility and sexual function. A systematic review was conducted, and articles were selected for review following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Risk of Bias was assessed using Methodological Index for Non-Randomized Studies (MINORS) criteria. The Oxford Levels of Evidence and Grades of Recommendation were utilized. RESULTS: A total of 69 studies were included for analysis. Most manuscripts contain level 3 or 4 evidence from single-center retrospective reports, leading to a grade D recommendation. MINORS assessment revealed a high risk of bias in most studies. J-pouch reconstruction may result in fewer daily stools than straight ileoanal anastomosis. There are no differences in complications based on the type of reconstruction. The timing of surgery should be individualized to patients and does not affect complications. Immunosuppressants do not appear to increase surgical site infection rates. Laparoscopic approaches result in longer operative times but shorter lengths of stay and fewer small bowel obstructions. Overall, complications are not different using an open or minimally invasive approach. CONCLUSIONS: There is currently low-level evidence related to certain aspects of surgical management for UC, including timing, reconstruction type, use of minimally invasive techniques, need for diversion, and risks to fertility and sexual function. Multicenter, prospective studies are recommended to better answer these questions and ensure the best evidence-based care for our patients. LEVEL OF EVIDENCE: Level of evidence III. STUDY TYPE: Systematic review.

Upper Gastrointestinal Series in the Workup for Pediatric Gastrostomy Placement: Does it Delay Care?

INTRODUCTION: Upper gastrointestinal (UGI) series is often part of the workup prior to the placement of gastrostomy tubes in children. Prior studies have suggested UGI to be limited in utility and an extra financial burden. The goal of this study was to investigate the utility and cost of UGI studies. METHODS: A retrospective, case control study of patients aged < 18 y receiving gastrostomy tubes at a free-standing children's hospital between 2012 and 2017. Total costs were obtained from the Pediatric Health Information System. RESULTS: Six hundred eighty five patients underwent gastrostomy placement during the study period. UGI was obtained in 90.8% of patients; 23.6% of studies were abnormal. The most common abnormal findings were reflux (13.8%) and abnormal anatomy (5.8%). The median time to obtain a UGI was 0.82 d (interquartile range 0.22-1.05). Obtaining a UGI was associated with delayed care in 104 patients (15.2%). If a delay was encountered, median time was 2.47 d (interquartile range 1.86-2.99). Ladd's procedures were performed in 12 patients (1.7%) found to have malrotation on UGI. None of the 63 patients who did not undergo UGI required a Ladd's procedure. Patients that had a UGI did not experience an increase in overall length of stay (14.3 versus 15.6 d, excluding intensive care unit patients), operative time (34 versus 39 min), or a change in rate of operative complications (11.5% versus 14.3%). In addition, UGI did not have a significant impact on total adjusted costs ($49,844 versus $83,438 without UGI, P = 0.12) but did slightly increase total adjusted costs per day ($2212 versus $1999 without UGI, P = 0.01). CONCLUSIONS: UGI prior to gastrostomy placement in children rarely identified abnormal findings that changed the operative plan, was associated with delayed care in 15% of patients, and was associated with slightly increased costs per day. Further analyses to identify subsets of children that may benefit from routine UGI are warranted.

Predicting wind-driven spatial deposition through simulated color images using deep autoencoders.

For centuries, scientists have observed nature to understand the laws that govern the physical world. The traditional process of turning observations into physical understanding is slow. Imperfect models are constructed and tested to explain relationships in data. Powerful new algorithms can enable computers to learn physics by observing images and videos. Inspired by this idea, instead of training machine learning models using physical quantities, we used images, that is, pixel information. For this work, and as a proof of concept, the physics of interest are wind-driven spatial patterns. These phenomena include features in Aeolian dunes and volcanic ash deposition, wildfire smoke, and air pollution plumes. We use computer model simulations of spatial deposition patterns to approximate images from a hypothetical imaging device whose outputs are red, green, and blue (RGB) color images with channel values ranging from 0 to 255. In this paper, we explore deep convolutional neural network-based autoencoders to exploit relationships in wind-driven spatial patterns, which commonly occur in geosciences, and reduce their dimensionality. Reducing the data dimension size with an encoder enables training deep, fully connected neural network models linking geographic and meteorological scalar input quantities to the encoded space. Once this is achieved, full spatial patterns are reconstructed using the decoder. We demonstrate this approach on images of spatial deposition from a pollution source, where the encoder compresses the dimensionality to 0.02% of the original size, and the full predictive model performance on test data achieves a normalized root mean squared error of 8%, a figure of merit in space of 94% and a precision-recall area under the curve of 0.93.

Surgical outcomes in children with Trisomy 13: An ACS NSQIP - Pediatric review.

BACKGROUND: Trisomy 13 is a rare genetic condition with a characteristic set of severe congenital abnormalities. Traditionally, the standard of care was to provide palliative care only. However, there has been a recent shift towards life-prolonging care, including surgery. This study seeks to describe surgical outcomes in patients with trisomy 13 and compare them to comorbidity-matched controls. METHODS: Using the ACS NSQIP Pediatric 2012-2019 Participant Use Data Files, patients with trisomy 13 were identified and described. A nearest-neighbor 10:1 propensity score match was performed using demographics, comorbidities, and procedural details. This yielded 254 patients with trisomy 13 and 2,422 controls. Risk ratios for morbidity and mortality by trisomy 13 status were determined using modified Poisson regression. The primary outcomes were thirty-day mortality and the occurrence of any morbidity. RESULTS: The median age of patients with trisomy 13 was 16 months (IQR 87 months). 126 were male (49.6%) and 128 were female (50.4%). There were no differences in overall morbidity compared to controls (31.8% vs. 29.7%, RR 1.06, 95%CI 0.87-1.28, p = 0.554), but patients with trisomy 13 had markedly higher mortality (7.9% vs. 1.8%, RR 4.43, 95%CI 2.28-8.61, p<0.001). CONCLUSIONS: We conclude that patients with trisomy 13 undergoing surgery have frequent morbidity and an elevated although not prohibitive risk of death. Compared to patients with similar comorbidities, they have similar rates of morbidity but a markedly higher risk of mortality. Parents of children with trisomy 13 require thorough counseling on these risks before deciding on surgery.

The Impact of the Maritime Deployment Cycle on the Surgeon's Knowledge, Skills, and Abilities.

INTRODUCTION: The U.S. Navy routinely deploys aircraft carriers and amphibious assault ships throughout the world in support of U.S. strategic interests, each with an embarked single surgeon team. Surgeons and their teams are required to participate in lengthy pre-deployment shipboard certifications before each deployment. Given the well-established relationship of surgeon volume to patient outcome, we aim to compare the impact of land vs. maritime deployments on Navy general surgeon practice patterns. MATERIALS AND METHODS: Case logs and pre-deployment training initiation of land-based (n = 8) vs. maritime-based (n = 7) U.S. Navy general surgeons over a 3-year period (2017-2020) were compared. Average cases per week were plotted over 26 weeks before deployment. Student's t-test was utilized for all comparisons. RESULTS: Cases declined for both groups in the weeks before deployment. At 6 months (26 weeks) before deployment, land-based surgeons performed significantly more cases than their maritime colleagues (50.3 vs. 14.0, P = .009). This difference persisted at 16 weeks (13.1 vs. 1.9, P = .011) and 12 weeks (13.1 vs. 1.9, P = .011). Overall, surgeon operative volume fell off earlier for maritime surgeons (16 weeks) than land-based surgeons (8 weeks). Within 8 weeks of deployment, both groups performed a similarly low number of cases as they completed final deployment preparations. CONCLUSIONS: Surgeons are a critical component of combat causality care teams. In this analysis, we have demonstrated that both land- and maritime-based U.S. Navy surgeons have prolonged periods away from clinical care before and during deployments; for shipboard surgeons, this deficit is large and may negatively impact patient outcomes in the deployed maritime environment. The authors describe this discrepancy and provide practical doctrinal solutions to close this readiness gap.

Regional air transportation of ovarian tissue for cryopreservation in a prepubertal female with cancer.

Ovarian tissue cryopreservation is the only fertility preservation (FP) option available to prepubescent females receiving gonadotoxic therapy, but it has limited availability. A 6-year-old female was diagnosed with high-risk rhabdomyosarcoma, and the planned treatment carried an 80% risk of ovarian failure. Her parents desired FP, but the nearest center was 500 miles away. The patient underwent oophorectomy at the cancer center with air transport of the tissue to the oncofertility center, where it was successfully cryopreserved. Formation of networks between full-service and limited oncofertility centers in a hub-and-spoke model would increase access to FP services, particularly in children.

Respiratory Syncytial Virus Bronchiolitis Complicated by Necrotizing Enterocolitis: A Case Series.

In rare instances, severe respiratory syncytial virus (RSV) infections of the lower respiratory tract can cause life-threatening extrapulmonary complications. In this report, we describe 4 previously healthy, term and late-preterm infants admitted to the PICU with respiratory failure due to RSV bronchiolitis who developed necrotizing enterocolitis shortly after admission. All infants exhibited progressive abdominal distention, had typical radiographic findings, and developed simple or complex ascites. In addition to being managed with broad-spectrum antibiotics and bowel rest, 1 infant was treated with colon resection and ileostomy, 2 had peritoneal drainage procedures for ascites, and one of those later developed small bowel strictures treated with delayed resection and anastomosis. Three were discharged from the hospital without further complications; 1 died of septic shock. In this case series, we describe development of necrotizing enterocolitis in otherwise healthy neonates with severe RSV disease in the absence of traditional risk factors. We hypothesize that a dysregulated proinflammatory response associated with severe RSV disease may alter intestinal blood flow and compromise barriers to bacterial translocation. Enteral feeding intolerance, septic ileus, and/or complex ascites may represent important clinical corollaries in these patients.

Poisson Probability of Failing to Meet Minimum Case Volumes in Pediatric Surgery Fellowships.

INTRODUCTION: With the expansion of pediatric surgery fellowships from 2008 to 2018, there is concern for the dilution of training experience, especially for rare index cases. The Accreditation Council for Graduate Medical Education (ACGME) established required minimum case numbers by case type, but this is a program requirement rather than an individual trainee requirement. The American Board of Surgery (ABS) is considering instituting minimum case requirements across 5 broad categories for individuals to be board-eligible in pediatric surgery. METHODS: The ACGME National Data Report summary case logs were obtained for graduating fellows in pediatric surgery from 2008 to 2018. Median case volumes were compared to minimum ACGME case numbers and proposed ABS individual requirements. Using Poisson distributions, probabilities of individual fellows failing to meet minimum case numbers were calculated. RESULTS: The average annual probability that a median program would fail to meet minimum ACGME case numbers in at least 1 category was estimated at 16.6%. Using the proposed ABS system, the probability of failure was estimated at 44.1%. No temporal trend was found in the annual probability of failure in either the ACGME or the proposed ABS system. CONCLUSIONS: There is significant risk of a fellow failing to meet case minimums in the ACGME system and the proposed ABS system. This probability is increased for the half of programs below median. If the ABS institutes case minimums as a requirement for certification in pediatric surgery, the current training paradigm may be impacted at some programs.

Surgical and anesthetic management for hepatectomy in two pediatric patients with trisomy 18, pulmonary hypertension, and hepatoblastoma.

Children with trisomy 18 are surviving longer and undergoing more aggressive life-sustaining therapy. This report describes two patients with trisomy 18 and hepatoblastoma (HB) successfully resected in the setting of significant pulmonary hypertension. Forty-four previously published cases of the association between HB and trisomy 18 are reviewed. With careful multidisciplinary preoperative planning, successful resection of HB in children with trisomy 18 who have significant pulmonary hypertension is feasible. Because HB and trisomy 18 are increasing in prevalence, the need for timely liver tumor resection in the setting of pulmonary hypertension will be more common.

Methods of Responsibly Managing End-of-Life Foams and Plastics Containing Flame Retardants: Part II.

This is Part II of a review covering the wide range of issues associated with all aspects of the use and responsible disposal of foam and plastic wastes containing toxic or potentially toxic flame retardants. We identify basic and applied research needs in the areas of responsible collection, pretreatment, processing, and management of these wastes. In Part II, we explore alternative technologies for the management of halogenated flame retardant (HFR) containing wastes, including chemical, mechanical, and thermal processes for recycling, treatment, and disposal.

Methods of Responsibly Managing End-of-Life Foams and Plastics Containing Flame Retardants: Part I.

Flame retardants (FRs) are added to foams and plastics to comply with flammability standards and test requirements in products for household and industrial uses. When these regulations were implemented, potential health and environmental impacts of FR use were not fully recognized or understood. Extensive research in the past decades reveal that exposure to halogenated FRs, such as those used widely in furniture foam, is associated with and/or causally related to numerous health effects in animals and humans. While many of the toxic FRs have been eliminated and replaced by other FRs, existing products containing toxic or potentially toxic chemical FRs will remain in use for decades, and new products containing these and similar chemicals will permeate the environment. When such products reach the end of their useful life, proper disposal methods are needed to avoid health and ecological risks. To minimize continued human and environmental exposures to hazardous FR chemicals from discarded products, waste management technologies and processes must be improved. This review discusses a wide range of issues associated with all aspects of the use and responsible disposal of wastes containing FRs, and identifies basic and applied research needs in the areas of responsible collection, pretreatment, processing, and management of these wastes.

International challenge to model the long-range transport of radioxenon released from medical isotope production to six Comprehensive Nuclear-Test-Ban Treaty monitoring stations.

After performing a first multi-model exercise in 2015 a comprehensive and technically more demanding atmospheric transport modelling challenge was organized in 2016. Release data were provided by the Australian Nuclear Science and Technology Organization radiopharmaceutical facility in Sydney (Australia) for a one month period. Measured samples for the same time frame were gathered from six International Monitoring System stations in the Southern Hemisphere with distances to the source ranging between 680 (Melbourne) and about 17,000 km (Tristan da Cunha). Participants were prompted to work with unit emissions in pre-defined emission intervals (daily, half-daily, 3-hourly and hourly emission segment lengths) and in order to perform a blind test actual emission values were not provided to them. Despite the quite different settings of the two atmospheric transport modelling challenges there is common evidence that for long-range atmospheric transport using temporally highly resolved emissions and highly space-resolved meteorological input fields has no significant advantage compared to using lower resolved ones. As well an uncertainty of up to 20% in the daily stack emission data turns out to be acceptable for the purpose of a study like this. Model performance at individual stations is quite diverse depending largely on successfully capturing boundary layer processes. No single model-meteorology combination performs best for all stations. Moreover, the stations statistics do not depend on the distance between the source and the individual stations. Finally, it became more evident how future exercises need to be designed. Set-up parameters like the meteorological driver or the output grid resolution should be pre-scribed in order to enhance diversity as well as comparability among model runs.

Future loss of Arctic sea-ice cover could drive a substantial decrease in California's rainfall.

From 2012 to 2016, California experienced one of the worst droughts since the start of observational records. As in previous dry periods, precipitation-inducing winter storms were steered away from California by a persistent atmospheric ridging system in the North Pacific. Here we identify a new link between Arctic sea-ice loss and the North Pacific geopotential ridge development. In a two-step teleconnection, sea-ice changes lead to reorganization of tropical convection that in turn triggers an anticyclonic response over the North Pacific, resulting in significant drying over California. These findings suggest that the ability of climate models to accurately estimate future precipitation changes over California is also linked to the fidelity with which future sea-ice changes are simulated. We conclude that sea-ice loss of the magnitude expected in the next decades could substantially impact California's precipitation, thus highlighting another mechanism by which human-caused climate change could exacerbate future California droughts.