Northwestern North America has experienced an exceptional heatwave in late June 2021 with many new temperature records across western Canada, Oregon and Washington states. Here we use a recent ...atmospheric reanalysis and a conditional approach based on dynamical adjustment to assess and quantify the influence of atmospheric circulation and other driving factors to the heatwave magnitude during the June 28–30 period. A blocking anticyclone, enhanced low‐level moisture and clear‐sky downward long‐wave radiation are shown to be the main factors of the heatwave persistence and magnitude. The heatwave magnitude is mainly attributable to internal variability with climate change being an additional factor (10%). Consequences of a similar atmospheric circulation anomaly in different phases of the Pacific Decadal Oscillations and in a warmer world at different global warming levels (1, 2, 3, and 4°C) are explored based on a single model initial‐condition large ensemble.
Plain Language Summary
Gathering robust statistics and performing extreme event attribution for very rare heat extreme events, such as the 2021 Northwestern North American heatwave, remain challenging due to incomplete sampling of weather data (∼100 years) challenging the application of extreme value theory and caveats related to the use of imperfect climate models in estimating likelihood changes between worlds with and without human influence. Here we use the dynamical adjustment method to quantify the key factors responsible for the magnitude and persistence of the heatwave. Dynamical adjustment aims to identify the causal factors that led to the heatwave with an approach conditional on the observed atmospheric circulation during the event. We find that natural variability is the main driver of the heatwave extreme magnitude with a small contribution from climate change. We also find that the heatwave spatial pattern mainly comes from the atmospheric circulation‐related component (the dynamic component). We investigate a possible contribution due the strong negative phase of the Pacific Decadal Oscillation observed in June 2021 and find it to be rather small. Finally, we ask whether future climate change can make a future similar event even more extreme. We find that the dynamic component would increase by 4°C in a 2°C warmer global climate.
Key Points
A blocking ridge, enhanced moisture and clear‐sky downward long‐wave radiation are the main causes of the heatwave magnitude and duration
The circulation‐induced heatwave component is the main driver of the heatwave pattern and magnitude with a minor role for climate change
A similar blocking event in a 2°C warmer climate would lead to a 4°C increase of the circulation‐induced heatwave component
Ozone depletion led to a positive trend in the summertime Southern Annular Mode (SAM) during the last decades of the 20th century. During the present century, global warming (GW) is expected to ...contribute to a positive SAM trend while ozone recovery is expected to act in the opposite direction. Here, Southern Hemisphere (SH) circulation and regional precipitation change are studied with a methodology that separates the effects from GW and ozone depletion/recovery. Our results show that a “tug‐of‐war” between ozone and GW occurs in the summertime stratosphere, propagating to the troposphere where it is manifest in the SAM. However, at the regional scale this “tug‐of‐war” is not as relevant as the combined effects of other remote drivers of circulation change, which force different kinds of precipitation changes in the SH. For regional precipitation changes, the uncertainty in future circulation change is as important as the uncertainty in the GW level.
Plain Language Summary
In the Southern Hemisphere, both ozone depletion and global warming have influenced climate in the past decades. Ozone recovery is expected to reverse the influence of ozone depletion, but the influence of global warming is expected to grow. Here, we investigate the combined effects of these anthropogenic forcings through the second half of the 20th century and the entire 21st century, quantifying their influence on stratospheric and tropospheric circulation and on regional precipitation changes. We find that the summertime stratosphere is affected by a “tug‐of‐war” between these two forcings, and that its effect propagates downward to the tropospheric circulation. On the other hand, summer precipitation in the land areas of the SH that are expected to experience large effects of climate change are not strongly affected by this “tug‐of‐war,” but are instead influenced by the effects of both stratospheric and tropical tropospheric changes.
Key Points
Long‐term changes in the delay of the breakdown of the Southern Hemisphere stratospheric polar vortex can be largely explained by a linear response to ozone‐depleting substances and to global warming
The tug‐of‐war between ozone recovery and global warming manifests itself in the stratospheric vortex breakdown delay and propagates to the troposphere
The uncertainty in future changes in regional precipitation in the Southern Hemisphere is subject to the combined effects of the uncertainty in tropical warming and in the vortex breakdown delay
We apply a physical climate storyline approach to an autumn flood event in the West Coast of Norway caused by an atmospheric river to demonstrate the value and challenges of higher spatial and ...temporal resolution in simulating flood impacts. We use a modelling chain whose outputs are familiar and used operationally, for example to issue flood warnings. With two different versions of a hydrological model, we show that (1) the higher spatial resolution between the global and regional climate model is necessary to realistically simulate the high spatial variability of precipitation in this mountainous region and (2) only with hourly data are we able to capture the fast flood-generating processes leading to the peak streamflow. The higher resolution regional atmospheric model captures the fact that with the passage of an atmospheric river, some valleys receive high amounts of precipitation and others not, while the coarser resolution global model shows uniform precipitation in the whole region. Translating the event into the future leads to similar results: while in some catchments, a future flood might be much larger than a present one, in others no event occurs as the atmospheric river simply does not hit that catchment. The use of an operational flood warning system for future events is expected to facilitate stakeholder engagement.
Attribution of high-impact weather events to anthropogenic climate change is important for disentangling long-term trends from natural variability and estimating potential future impacts. Up to this ...point, most attribution studies have focused on univariate drivers, despite the fact that many impacts are related to multiple compounding weather and climate drivers. For instance, co-occurring climate extremes in neighbouring regions can lead to very large combined impacts. Yet, attribution of spatially compounding events with different hazards poses a great challenge. Here, we present a comprehensive framework for compound event attribution to disentangle the effects of natural variability and anthropogenic climate change on the event. Taking the 2020 spatially compounding heavy precipitation and heatwave event in China as a showcase, we find that the respective dynamic and thermodynamic contributions to the intensity of this event are 51% (35–67%) and 39% (18–59%), and anthropogenic climate change has increased the occurrence probability of similar events at least 10-fold. We estimate that compared to the current climate, such events will become 10 times and 14 times more likely until the middle and end of the 21st century, respectively, under a high-emissions scenario. This increase in likelihood can be substantially reduced (to seven times more likely) under a low-emissions scenario. Our study demonstrates the effect of anthropogenic climate change on high-impact compound extreme events and highlights the urgent need to reduce greenhouse gas emissions.
Climate model resolution can affect both the climate change signal and present‐day representation of extreme precipitation. The need to parametrize convective processes raises questions about how ...well the response to warming of convective precipitation extremes is captured in such models. In particular, coastal precipitation extremes can be sensitive to sea surface temperature (SST) increase. Taking a recent coastal precipitation extreme as a showcase example, we explore the added value of convection‐permitting models by comparing the response of the extreme precipitation to a wide range of SST forcings in an ensemble of regional climate model simulations using parametrized and explicit convection. Compared at the same spatial scale, we find that the increased local intensities of vertical motion and precipitation in the convection‐permitting simulations play a crucial role in shaping a strongly nonlinear extreme precipitation response to SST increase, which is not evident when convection is parametrized. In the convection‐permitting simulations, SST increase causes precipitation intensity to increase only until a threshold is reached, beyond which further SST increase does not enhance the precipitation. This flattened response results from an improved representation of convective downdrafts and near‐surface cooling, which damp the further intensification of precipitation by stabilizing the lower troposphere locally and also create cold pools that cause subsequent convection to be triggered at sea, rather than by the coastal orography. These features are not well represented in the parametrized convection simulations, resulting in precipitation intensity having a much more linear response to increasing SSTs.
Key Points
Extreme precipitation response to SST increase can be highly nonlinear
Spatial variability of subgrid‐scale vertical motions inadequately parametrized
Convection‐permitting models therefore needed to capture precipitation response
Abstract
Two methods exist to address the degree to which past extreme events and associated disasters will be intensified due to climate change: storyline approaches and risk-based approaches. ...However, the risk-based approach applied to weather similar to the target event (typhoons, a stationary weather front,…etc) becomes theoretically similar to the storyline approach. We examine this theory for the climate change impact of a real event, Typhoon Hagibis, which caused devastating flood damage to eastern Japan in 2019, while focusing on basin-averaged accumulated rainfall (BAAR) in major eastern river basins. A risk-based approach was conducted to determine the future change of BAAR by calculating the quantile change corresponding to Hagibis from the probability distribution of typhoon-induced events in a large ensemble climate simulation dataset database for Policy Decision-making for Future climate change (past, +2K and +4K future climates). A storyline approach for Typhoon Hagibis was realized using a pseudo global warming (PGW) experiment with a 5 km non-hydrostatic model. The projected BAAR in the two approaches were consistent for all target basins, supporting the robustness of the calculated changes in extreme catchment precipitation. This presents an important practical benefit: one can assess future climate change impact on a past symbolic event using either PGW experiments or large ensemble climate projections for the target weather.
Through qualitative interviews and self-administrated online surveys, this study critically examines how 104 first-year student teachers experience The Scottish Storyline Approach, a cross-curricular ...approach to teaching and learning. Framed by Dewey's (2005) concept of experience, The Storyline Approach is discussed as a possible didactic tool for making teaching and learning meaningful. Although not all students experience Storyline as positive, this study finds that the majority of the students report Storyline as relevant for their future profession.
•The demands on teachers of the 21st century require alternative approaches to teaching and learning.•Storyline provides one alternative approach to teaching and learning for student teachers in their education.•71% student teachers described their experience with The Storyline Approach as good or excellent.•86% student teachers experience The Storyline Approach as relevant for their future profession.•Experiencing The Storyline Approach influences student teachers' attitude towards implementing Storyline in the future.
Climate scientists have proposed two methods to link extreme weather events and anthropogenic climate forcing: the probabilistic and the storyline approach. Proponents of the first approach have ...raised the criticism that the storyline approach could be overstating the role of anthropogenic climate change. This issue has important implications because, in certain contexts, decision-makers might seek to avoid information that overstates the effects of anthropogenic climate change. In this paper, we explore two research questions. First, whether and to what extent the storyline approach overstates the effects of anthropogenic climate change. Second, whether the objections offered against the storyline approach constitute good reasons to prefer the probabilistic approach. Concerning the first question, we show that the storyline approach does not necessarily overstate the effects of climate change, and particularly not for the reasons offered by proponents of the probabilistic approach. Concerning the second question, we show, independently, that the probabilistic approach faces the same or very similar objections to those raised against the storyline approach due to the lack of robustness of climate models and the way events are commonly defined when applying the probabilistic approach. These results suggest that these objections might not constitute good reasons to prefer the probabilistic approach over the storyline approach.
This article presents a six-week long action research study in two primary school classes, with the aim of exploring how a Storyline approach can facilitate learning and acting on sustainability ...issues, and how this approach might enhance pupils' agency. This study is underpinned by and analyzed through theories of relational pedagogy, in which communication processes and interaction are central aspects of the learning process. The empirical material consists of video observations from classroom situations. The results show relational aspects of the teacher's work in a Storyline and highlight the importance of the teacher's caring role Storyline instruction. Further, results suggest that the reflective process entails critical thinking and has potential to support development of pupils' democratic capabilities, including a civic dimension. This action research study adds to evidence concerning how relational agency has been exercised and performed through features of a Storyline.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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