Global climate change is often thought of as a steady and approximately predictable physical response to increasing forcings, which then requires commensurate adaptation. But adaptation has practical, cultural and biological limits, and climate change may pose unanticipated global hazards, sudden changes or other surprises, as may societal adaptation and mitigation responses. We outline a strategy for better accommodating these challenges by making climate science more integrative, in order to identify and quantify known and novel physical risks even–or especially–when they are highly uncertain, and to explore risks and opportunities associated with mitigation and adaptation responses by engaging across disciplines. This improves the chances of anticipating potential surprises and identifying and communicating “safe landing” pathways that meet UN Sustainable Development Goals and guide humanity toward a better future.

The Southern Hemisphere storm track is a key component of the Earth's global circulation patterns, with a prominent role in the movement of heat and momentum across the mid-latitudes, and a controlling influence over the behaviour of synoptic eddies. Storm track characteristics are expected to change with anthropogenic forcings, leading to changes in regional weather patterns, and impacting communities through its influence on extreme events. We document projected storm track climatologies at the end of the 21st century under high- and low-emissions scenarios using the CMIP6 generation of models. We find previously described projections -- the poleward migration of the storm track, and intensification of storm activity -- persist in CMIP6. We explore projections of spatio-temporal variability of the Southern Annular Mode, and consequences for the storm track.

ERA5 reanalysis is used to examine extreme precipitation using a spatially dependent precipitation threshold applied within a cyclone compositing framework. This is used to account for regional variation in precipitation generating processes within Southern Hemisphere mid-latitude cyclones across the cyclone lifecycle. The spatial extent of extreme precipitation is limited to a smaller region around the cyclone centre compared to non-extreme precipitation, though extreme precipitation displays a good spatial correlation with non-extreme precipitation. Extreme precipitation occurs more often during the deepening phase of the cyclone before it reaches a maximum depth. Precipitation occurrence at the 90th and 98th percentiles reduces to 46% and 30% of the deepening value across the cyclone lifecycle, averaged over the composite. Precipitation fraction at the 90th and 98th percentile reduces to 80% and 60% of the deepening value. Our methodology provides a quantitative assessment of precipitation extremes both spatially and temporally, within a cyclone compositing framework.

ERA5 reanalysis output is compared to WindSat measurements over cyclones at Southern Hemisphere mid- to high-latitudes. WindSat provides an independent measure of how well ERA5 represents cyclones, as WindSat is not assimilated into ERA5. We implement a tracking scheme to identify cyclone centres and tracks, before using cyclone composites to match concurrent data in ERA5 and WindSat. We find that both ERA5 and WindSat show comparable spatial structures for low level wind speed, total column water vapour, cloud liquid water and precipitation. Compared to WindSat, ERA5 underestimates total column water vapour by up to 5\% and cloud liquid water by up to 40\%. ERA5 underestimates precipitation in the warm sector by up to 15\%, but overestimates in the cold sector by up to 60\%. Similar biases in ERA5 are seen when comparing to AMSR-E data, even though AMSR-E radiances are assimilated into ERA5. Comparing ERA5 and WindSat across the cyclone lifecycle, a strong correlation is seen across the cyclone as it deepens and reaches peak intensity, before slightly declining as the cyclone decays. In the cold sector ERA5 shows underestimation of cloud liquid water, yet overestimates precipitation at all lifecycle stages. However, in the warm sector precipitation is underestimated. This potentially suggests the presence of biases within the ERA5 parameterisations of cloud and precipitation causing a disconnect between the two. Despite this, ERA5 shows strong correlation with WindSat and determines cyclone structure well across the cyclone lifecycle, showing its value for use in cyclone compositing analysis.

Storm tracks are a key component of global atmospheric circulation. Their influence ranges from macro- to mesoscale dynamics, from large-scale movement of heat and momentum to extreme weather events. The scale of their impact makes understanding storm track dynamics critical to forecasting and climate projections. In this study, we assess CMIP6 historical experiment fidelity to observations of the Southern Hemisphere storm track. Specifically, storm track climatology, variability, and its interactions with low-frequency variability, with the aim of providing confidence for projections of future climate. We find CMIP6 models replicate results from the ERA-5 reanalysis with high fidelity in some regards; namely, capturing climatology of the 500hPa geopotential height field, the role of large-scale variability, and the baroclinic connection with high-frequency variability. However, models fail to capture the magnitude and variability of the storm track, particularly canonical zonal asymmetry. Our results indicate the importance of the storm track is underestimated in CMIP6.

The Track Zero Charitable Trust (http://trackzero.nz) was founded in early 2018 with the goal of inspiring action on climate change through engagement with the arts. The main motivation is that artistic expression connects on an emotional level in a way that direct communication of science does not. Also, around 80 percent of New Zealanders engage in some way with the arts, a much larger audience than those who take an active interest in science. This presentation discusses the first major activity of TrackZero, a series of public meetings around New Zealand where scientists partnered with local arts practitioners to interact with audiences on the science, on people’s feelings and concerns, and on ways forward to action on adapting to or mitigating climate change. Different communities had different concerns and the range of conversations was rich and varied. While no formal evaluation has been carried out, we provide some general reflections on impact and engagement, and ideas for future activities.

This work provides an updated set of 12 dominant geopotential height fields - or ‘regimes’ - over Aotearoa New Zealand. These regimes were initially produced by Kidson (2000) and have provided the basis for many other subsequent studies. These maps provide a guide to the prevailing weather due to the broad equivalence of 1000hPa geopotential height and mean-sea-level pressure. The results presented here are broadly in agreement with previous work but with some important differences. The most notable of these being the need to average two blocking regimes together to provide good agreement between this work and Kidson (2000). These differences are attributed to the software used, improvements to the underlying dataset itself and to the ‘mixing’ of statistically indistinguishable empirical orthogonal functions - EOFs - in different linear combinations. All data and code used in this work is publicly accessible and it is hoped that this will provide a catalyst for open discussions on this topic, particularly with relation to future perturbations to these regimes under climate change.