Robust but weak winter atmospheric circulation response to future Arctic sea ice loss.

The possibility that Arctic sea ice loss weakens mid-latitude westerlies, promoting more severe cold winters, has sparked more than a decade of scientific debate, with apparent support from observations but inconclusive modelling evidence. Here we show that sixteen models contributing to the Polar Amplification Model Intercomparison Project simulate a weakening of mid-latitude westerlies in response to projected Arctic sea ice loss. We develop an emergent constraint based on eddy feedback, which is 1.2 to 3 times too weak in the models, suggesting that the real-world weakening lies towards the higher end of the model simulations. Still, the modelled response to Arctic sea ice loss is weak: the North Atlantic Oscillation response is similar in magnitude and offsets the projected response to increased greenhouse gases, but would only account for around 10% of variations in individual years. We further find that relationships between Arctic sea ice and atmospheric circulation have weakened recently in observations and are no longer inconsistent with those in models.

Quantifying the influence of short-term emission reductions on climate.

The COVID-19 (coronavirus disease 2019) pandemic has resulted in a marked slowdown in greenhouse gas and aerosol emissions. Although the resulting emission reductions will continue to evolve, this will presumably be temporary. Here, we provide estimates of the potential effect of such short-term emission reductions on global and regional temperature and precipitation by analyzing the response of an Earth System Model to a range of idealized near-term emission pathways not considered in available model intercomparison projects. These estimates reveal the modest impact that temporary emission reductions associated with the COVID-19 pandemic will have on global and regional climate. Our simulations suggest that the impact of carbon dioxide and aerosol emission reductions is actually a temporary enhancement in warming rate. However, our results demonstrate that even large emission reductions applied for a short duration have only a small and likely undetectable impact.

Impact of polar ozone depletion on subtropical precipitation.

Over the past half-century, the ozone hole has caused a poleward shift of the extratropical westerly jet in the Southern Hemisphere. Here, we argue that these extratropical circulation changes, resulting from ozone depletion, have substantially contributed to subtropical precipitation changes. Specifically, we show that precipitation in the southern subtropics in austral summer increases significantly when climate models are integrated with reduced polar ozone concentrations. Furthermore, the observed patterns of subtropical precipitation change, from 1979 to 2000, are very similar to those in our model integrations, where ozone depletion alone is prescribed. In both climate models and observations, the subtropical moistening is linked to a poleward shift of the extratropical westerly jet. Our results highlight the importance of polar regions for the subtropical hydrological cycle.

Innominate osteotomy in Perthes disease.

A retrospective study was performed in 27 patients who underwent innominate osteotomy for the treatment of severe Perthes disease. Time intervals between surgery and final follow-up ranged from 5 years to 16 years 4 months. Preoperative and postoperative periods of treatment were often more prolonged than those reported by Salter. One-half of the patients were less than 6 years of age at onset of the disease. A number of patients had significant deformity of the femoral head. Nevertheless, clinically good or fair results were obtained in 88% of the patients and poor results were found in 12%.

Long-term results of displaced talar neck fractures.

Of 36 fractures of the talar neck without comminution of the body, eight were undisplaced, treated closed, and 28 were displaced and treated by open reduction. Twenty of the operations were less than 12 hours after injury. Nineteen of 20 were performed through a medial approach, six with a medial malleolar osteotomy. The long-term results were evaluated by a standard rating system based on classification by the fracture. A protective brace was developed for non-weight-bearing in two patients with complete avascular necrosis, and ankle protection with weight-bearing in ten with partial necrosis. Prompt open reduction and internal fixation, malleolar osteotomy, and protected weight-bearing are recommended in selected cases.