Critical slowing down suggests that the western Greenland Ice Sheet is close to a tipping point

The Greenland Ice Sheet (GrIS) is a potentially unstable component of the Earth system and may exhibit a critical transition under ongoing global warming. Mass reductions of the GrIS have substantial impacts on global sea level and the speed of the Atlantic Meridional Overturning Circulation, due to the additional freshwater caused by increased meltwater runoff into the northern Atlantic. The stability of the GrIS depends crucially on the positive melt-elevation feedback (MEF), by which melt rates increase as the overall ice sheet height decreases under rising temperatures. Melting rates across Greenland have accelerated nonlinearly in recent decades, and models predict a critical temperature threshold beyond which the current ice sheet state is not maintainable. Here, we investigate long-term melt rate and ice sheet height reconstructions from the central-western GrIS in combination with model simulations to quantify the stability of this part of the GrIS. We reveal significant early-warning signals (EWS) indicating that the central-western GrIS is close to a critical transition. By relating the statistical EWS to underlying physical processes, our results suggest that the MEF plays a dominant role in the observed, ongoing destabilization of the central-western GrIS. Our results suggest substantial further GrIS mass loss in the near future and call for urgent, observation-constrained stability assessments of other parts of the GrIS.

During the last century, the Greenland Ice Sheet (GrIS) has lost mass at an accelerating rate (1, 2). The mass loss is caused by solid ice discharge into the North Atlantic and surface melting due to increasing temperatures. The relative contribution of the latter has increased from 42% before 2005 to 68% between 2009 and 2012, and surface runoff caused 84% of the increase in mass reduction since 2009 (3). The complete melting of the GrIS would cause a global sea level rise of more than 7 m (4, 5). Continued melting of the GrIS has been suggested to potentially lead to a collapse of the Atlantic Meridional Overturning Circulation via increased freshwater flux into the North Atlantic (6, 7), which may, in turn, trigger a cascade of transitions in additional tipping elements such as the Amazon rainforest and the tropical monsoon systems (6, 8–10).In addition to the centennial-scale variability associated with the increasing trend in mean temperatures related to anthropogenic climate change, the pace of mass loss has decadal-scale fluctuations caused by natural variations in external oceanic and atmospheric forcing. The imprints of these natural, decadal-scale fluctuations are spatially heterogeneous across the GrIS. Since the early 2000s, periods of persistently negative phases of the North Atlantic Oscillation (NAO) and a positive phase of the East Atlantic Pattern (11) have led to a weakening and southward shift of the jet stream, and more persistent blocking (12) over Greenland during summer, resulting in overall increased mass reduction rates (2, 13). On the other hand, a slowing down of mass loss since 2013—which inverted again in 2019—was caused by more periods with a persistent positive NAO (14). Moreover, recent observations show that the Jakobshavn glacier has been advancing again since 2016 due to anomalous wintertime heat loss in the boundary current around southern Greenland (15). However, these natural fluctuations do not have a sustained impact on melt rates comparable to the longer-term trend toward overall increasing melt rates caused by anthropogenic global warming (Fig. 1A).Open in a separate windowFig. 1.(A) Summer sea level temperatures from the Ilulissat station in CWG (25) (blue curves) and Arctic temperature anomalies (26) (red curves). The linear trend of the station data (dashed blue curve) corresponds to 1.3 °C warming per century. Arctic temperature anomalies are shown only for comparison; only the station data (blue curves) are used for our analysis. (B) Melt rates from the CWG ice core stack (blue curve) and the NU peninsula core (red curve), given as z scores with respect to a normal distribution (18). (C) Detrended logarithmic CWG (blue curve) and NU (red curve) melt rates. A Gaussian filter with bandwidth σ=30 y was used for detrending. The runoff and melt time series are preprocessed in this way before computing the EWS indicators to exclude potential biases by underlying trends; in particular, we take the logarithm of the melt rates in order to account for skewed data distributions. (D) The variance of the CWG (blue curves) and NU (red curves) melt rates. (E) The AC1 of the CWG (blue curves) and NU (red curves) melt rates. Note that the AC1, despite a significantly positive trend, appears to have at least temporarily stabilized in the last few decades. It should be noted, however, that the AC1 is generally influenced by (multi)decadal variability (27). The window size for computing the variance and the AC1 is w=70 y, and values are plotted at the windows’ endpoints. Data for the first w=70 y are omitted to ensure that all windows contain the same number of data points. The dashed lines in D and E indicate linear trends of the variance and AC1, and P values for positive slopes as determined from a phase surrogate test are indicated in the legend (see Materials and Methods). The statistical significance of the positive trends is robust across wide ranges of the bandwidth σ and the sliding window size (SI Appendix, Fig. S1).Early model simulations suggest that melting of the GrIS is inevitable beyond a critical global mean temperature threshold of 0.8 °C to 3.2 °C above preindustrial levels, with a best estimate of 1.6 °C (16). More recent comprehensive modeling results show that, for the representative concentration pathway 8.5 (RCP8.5), the GrIS melts entirely until AD 3000 (5). Arctic temperatures have increased more than the global average (17) (Fig. 1A), and the nonlinear increase in GrIS melt rates and runoff that have recently been detected (18) (Fig. 1B) suggests that the critical temperature threshold may be closer than previously thought. We emphasize that the surface mass balance turning negative is not a necessary condition for stability loss, and the temperature may reach a critical threshold years before a turning point in the mass balance (16).Idealized models of critical transitions in natural systems suggest that the loss of stability of an equilibrium (fixed point) is observable before the abrupt transition (19). In dynamical systems with random forcing, one can show that, if a system approaches a bifurcation where an equilibrium point loses its stability, the variance of the fluctuations around the equilibrium will increase, as will the characteristic decay time of the autocorrelation function of these fluctuations. The change in dynamics that occurs as stability is lost is often called critical slowing down, and the associated statistical precursor signs in terms of rising variance and lag-one autocorrelation (AC1) are called early-warning signals (EWS) (19). Such statistical EWS associated with critical slowing down are, for example, detectable in the temperature proxy from the North Greenland Ice Core Project before several of the Dansgaard–Oeschger events of the last glacial interval (20, 21), as well as before other abrupt transitions in past climates (22). In the context of anthropogenic global warming, EWS are expected to precede potential abrupt transitions in the Earth system’s major tipping elements, such as the polar ice sheets, the Atlantic Meridional Overturning Circulation, or the tropical monsoon systems (23). We investigate here a possible tipping point for the GrIS based on the theory of critical slowing down.In the following, we will first show that central-western Greenland (CWG) melt rates exhibit robust and significant EWS. We then reconstruct the corresponding CWG ice sheet height changes and show that they can be captured well by a simple model focusing on the melt elevation feedback (MEF). We then demonstrate that pronounced EWS can also be found in the fluctuations of the reconstructed ice sheet height around the equilibrium of the model and show that these EWS are consistent with the theoretical expectations provided by the MEF model.     

基于电刺激的大鼠肌筋膜疼痛触发点的发生机制

目的:探究电刺激下肌筋膜疼痛触发点肌纤维的兴奋性和耐疲劳表现。方法:将48只雄性SD大鼠随机分为对照组(CG1、CG2、CG3)和触发点组(TG1、TG2、TG3)。CG1和TG1测试刺激阈值强度和最大收缩力量(MCF)以及其最适刺激强度;CG2和TG2测试不同刺激强度下MCF的变化;CG3和TG3测试不同刺激频率下MCF的变化。钝性打击结合离心运动造模8周,恢复4周后将大鼠接入生物机能测试系统,给予肌纤维一系列电刺激,测量比较各组引起肌肉收缩的阈值强度、MCF、刺激强度和频率诱导的肌肉疲劳等指标。结果:TG1组引起肌肉开始收缩的阈值强度和最大收缩力量(MCF)的最适刺激强度比CG1组低,具有显著性差异(P0.05);TG1组与CG1组的MCF无显著性差异(P0.05)。TG2组电刺激引起的MCF第15、20次增量电刺激低于第1、5、10次增量,具有高度显著性差异(P0.01);TG2组电刺激引起的MCF第10、15、20次增量CG2组,具有高度显著性差异(P0.01);TG2组电刺激引起的MCF第1、5、10次增量无显著性差异(P0.05);TG2组电刺激引起的MCF第1、5次增量与CG2组相比无显著性差异(P0.05)。TG3组电刺激引起MCF所需的刺激频率比CG3组低,呈高度显著性差异(P0.01);TG3组电刺激引起的MCF比CG3组低,具有显著性差异(P0.05)。结论:与正常肌纤维相比,触发点肌纤维对电刺激反应更敏感,受到连续电刺激时更易疲劳。     

一次性根充法治疗牙髓炎的疗效思路构建

目的：本文就一次性根充法应用于牙髓炎临床治疗中的价值进行了浅显的研究和探析。方法选择我单位口腔中心自2013年7月~2014年7月期间收治的牙髓炎患者68例,将其平均分为观察组和对照组,两组患者均34例,观察组行一次性根充法治疗,对照组行分次根充法治疗,对两组患者的治疗效果,疼痛程度及舒适程度进行观察和统计。结果观察组患者治疗总有效率明显高于对照组患者(<0.05);观察组患者疼痛评分明显低于对照组患者(<0.05);观察组患者舒适评分明显高于对照组患者(<0.05)。结论一次性根充法应用于牙髓炎临床治疗中的效果显著,有效减轻了患者的疼痛程度,值得推广。     

家庭康复护理对脑瘫患儿的意义及实施要点探析

目的：探讨家庭康复护理对脑瘫患儿的意义以及实施要点。方法选取脑瘫患儿患者80例,随机分为观察组和对照组,各40例。对照组出院后给予患儿家长常规健康宣教,观察组出院后对患儿家长实施专业培训,以确保患儿接受有效的家庭康复护理,并比较2组效果。结果观察组适应行为、大运动行为、精细运动行为、语言行为以及个人-社交行为评分分别为（67.9±5.3）、（70.2±4.6）、（64.3±7.1）、（62.5±4.3）、（60.3±4.7）,对照组分别为（48.6±6.7）、（58.9±5.2）、（41.2±5.3）、（41.6±5.1）、（41.2±5.9）,差异有统计学意义（P<0.05）。结论家庭康复护理在脑瘫患儿护理中的应用效果显著,对提高患儿康复效果具有重要作用,值得推广应用。     

气机升降针法治疗肝郁型失眠的临床观察

【目的】观察气机升降针法治疗肝郁型失眠患者的临床疗效。【方法】将符合纳入标准的60例失眠患者随机分为治疗组和对照组各30例。治疗组给予气机升降针法治疗,对照组给予常规针法治疗。观察2组治疗前后多导睡眠图（PSG）、匹兹堡睡眠质量指数（PSQI）及临床疗效变化情况。【结果】（1）治疗后,2组患者睡眠总时间、深睡眠时间及快速眼球运动（REM）睡眠时间均有所延长,睡眠潜伏期缩短,觉醒次数减少（P<0.05）。治疗组睡眠总时间、深睡眠时间以及REM睡眠时间改善作用优于对照组（P<0.05）。（2）治疗后,2组患者PSQI评分均降低（P<0.01）,治疗组降低作用优于对照组（P<0.01）。（3）治疗组和对照组总有效率分别为93.33%和76.67%,治疗组疗效优于对照组（P<0.01）。【结论】气机升降针法治疗肝郁型失眠与常规针法比较疗效更为显著,其操作简便,方法新颖。     

Evidence for Dry Needling in the Management of Myofascial Trigger Points Associated With Low Back Pain: A Systematic Review and Meta-Analysis

Objective

To evaluate the current evidence of the effectiveness of dry needling of myofascial trigger points (MTrPs) associated with low back pain (LBP).

What is the Role of Reversal Agents in the Management of Emergency Department Patients with Dabigatran-Associated Hemorrhage?

Background

In 2010, the U.S. Food and Drug Administration (FDA) approved dabigatran as the first non-warfarin oral anticoagulant for use in the United States. At the time of FDA approval, there was no antidote or effective treatment for dabigatran-induced hemorrhage. In 2015, the FDA approved idarucizumab for the treatment of dabigatran-induced hemorrhage. The purpose of this clinical practice statement is to evaluate the role of select reversal agents in the management of patients with dabigatran-associated bleeding.

浅谈人之“八纲脉”

人之脉象大体可从脉位、脉率、脉力、脉畅四个角度,分为浮和沉、迟和数、实和虚、滑和涩八种典型病脉,统称“八纲脉”。八纲脉为辨脉之提纲,可辨别病之表里、寒热、实虚、在气在血,为识脉辨证之捷径。证之临床,该方法提纲挈领,不仅有助于初学者去芜存菁,掌握脉学之要,而且直指临证,指导辨证论治。     

Comparison of isometric and anatomical graft placement in synthetic ACL reconstructions: A pilot study

Correct graft placement is critical to the success of anterior cruciate ligament reconstructions (ACLR). Whilst current trend is to insert the graft in an anatomical location, synthetic grafts have shown to better perform when they are located in an isometric position. Placement, however, is largely dependent on the surgeon and no consensus has been reached for synthetic grafts.Kinematic flexion-extension data of four separate cadaveric knees was obtained using an optical tracking system. Knees were CT-scanned and computer models were developed for each specimen. Three different graft insertion techniques were simulated in each of the computer models. Kinematic data obtained from the optical tracking was applied to the 3D computer models to simulate knee flexion-extension, and virtual change in ACL graft length was measured over the cycle for each insertion technique. Length changes were plotted onto the Radiological-Quadrant.The isometric region on the femur was found to be a band spreading from the mid to deep end of the Blumensaat's line down to the shallow-inferior end of the femoral condyle. The JP Laboureau isometric point technique was consistently located in the isometric zone, with the following coordinates on the Radiographic-Quadrant: t=0.375 (SD 0.0066), h=0.227 (SD 0.0266). The Bernard–Hertel and Charlie Brown anatomical placement methods were located (13%, ?6%) and (8%, ?15%) away, from the JP Laboureau isometric point, respectively, based on t- and h- coordinates of the Radiographic-Quadrant.This study has determined the isometric region using three-dimensional analysis relative to the Radiographic-Quadrant. The JP Laboureau method best finds the isometric point. This information is useful for synthetic graft placement.