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Journal articleReyes AV, Carlson AE, Clark J, et al., 2024,
Timing of Cordilleran-Laurentide ice-sheet separation: Implications for sea-level rise
, Quaternary Science Reviews, Vol: 328, ISSN: 0277-3791During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea-level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 10Be exposure ages along an ∼1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 ± 0.4 ka and ended by 13.8 ± 0.1 ka at ∼56°N. Ice-sheet model simulations consistent with the 10Be ages find that the saddle collapse contributed 6.2–7.2 m to global mean sea-level rise from ∼15.5 ka to ∼14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1–3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A ∼14.6-14.3 ka, constituting 20–40% of this meltwater pulse's volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1–2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed.
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OtherMurray-Watson R, Gryspeerdt E, 2024,
Air mass history linked to the development of Arctic mixed-phase clouds
<jats:p>The development of clouds during marine cold-air outbreaks (MCAOs) represent a complex phenomenon, transitioning from stratocumulus decks near ice edges to cumuliform fields downwind. This change cloud morphology changes the radiative properties of the cloud, and therefore is of importance to the surface energy budget. Therefore, it is crucial to understand the factors which may drive transition to a broken cloud field. Previous in situ and modelling studies suggest the formation of ice may enhance precipitation and therefore accelerate break-up. However, little is known about the development of mixed-phase clouds in MCAOs.&#160;This study uses pseudo-Lagrangian trajectories and satellite data to analyze this mixed-phase cloud development. We observe a rapid transition from liquid to ice phases in MCAO clouds, contrasting with similar cloud formations outside MCAO conditions. These mixed-phase clouds initially form at temperatures below -20&#176;C near ice edges but can dominate even at -13&#176;C further into outbreaks. This temperature shift suggests a significant role for biological ice nucleating particles (INPs), which increase in prevalence as air masses age over marine environments. The study also notes the influence of the air mass's history over snow- and ice-covered surfaces, which may be low in INPs, on cloud evolution. This link helps explain seasonal variations in Arctic cloud development, both during and outside of MCAOs. Our findings emphasize the importance of understanding local marine aerosol sources and the broader INP distribution in the Arctic for accurate cloud phase modeling in the region.&#160;</jats:p>
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OtherPonsonby J, Teoh R, Stettler M, 2024,
Towards an improved treatment of (semi) volatile particle activation in contrail models
<jats:p>Contrails are estimated to account for the majority of the present-day warming by the aviation industry. Their formation relies on the availability of aerosol in the exhaust plume, upon which water vapour can condense and subsequently freeze to form contrail ice crystals Most modern aircraft operate in the soot-rich regime, releasing soot particles with a number emission index (EIn) of between 1014 and 1016 (kg-fuel)-1. Under these conditions, the number concentration of soot particles and contrail ice crystals scales linearly. For this reason, existing global contrail simulations typically assume that the number concentration of ice crystals and soot particles are equivalent. However, the use of alternative fuels such as sustainable aviation fuel (SAF) and liquid hydrogen, and the adoption of cleaner lean-burn combustors in the existing fleet are likely to drive the soot EIn into the soot-poor regime < 1013 (kg-fuel)-1. Here, (semi) volatile material and entrained ambient particles can compete with soot for plume supersaturation and the relationship between the number concentration of soot particles and contrail ice crystals is non-linear. These effects are not currently accounted for in existing contrail models used to simulate regional and global contrail climate forcing. &#160;In this work, we extend the parcel model proposed by K&#228;rcher et al. [1] to account for the activation of volatile particulate matter (vPM) in the soot-poor regime and integrate this into the contrail cirrus prediction model (CoCiP) [2]. We explore the relationship between the soot EIn and the apparent ice emissions index (AEI) in the soot-rich and soot-poor regimes, evaluating the model&#8217;s sensitivity to different aerosol properties, including particle hygroscopicity and characteristics of the particle size distribution. Preliminary results show a linear relationship between the soot EIn and AEI in the soot-rich regime, consistent with
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OtherHoward B, Awuni C, Berkhout F, et al., 2024,
Co-production could improve the science-policy-practice nexus in hydrology: lessons from co-producing knowledge on flood risk in Tamale, Ghana
<jats:p>Understanding of hydrological risk is increasing but much of it remains non-actionable. Consequently, interventions are seldom informed by the latest insights, limiting their effectiveness and resilience, especially in a non-stationary world. The co-production of knowledge in hydrology can result in more salient, useful, and usable outcomes that are used to directly inform decisions. Co-production is an interactive and complex process founded on relationships between science, society, practice, and policy. We are applying this approach to generate locally relevant understanding, evidence, and action on flood risk in Tamale, a city of ~500,000 people in northern Ghana. A team of citizens, practitioners, policy makers, and researchers from a range of disciplines are working together to understand the drivers and distribution of flood risk, as well as the effects of top-down and citizen-led adaptation. Knowledge is generated and validated in a series of stages and cycles and operationalized in different modes for different users. Whilst this is an ongoing process which continues to evolve, in this talk I will share lessons and experiences from the co-production approach in Tamale that may be translatable to other contexts. Co-production approaches represent tangible frameworks to improve the science-policy-practice nexus in hydrology and water resources management, and sharing good examples can expedite adoption.</jats:p>
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OtherPrasow-Émond M, Plancherel Y, Mason PJ, et al., 2024,
Impacts of Climate Change on Small Island Nations: A Data Science Framework using Remote Sensing and Observational Time Series
<jats:p>Small Island Developing States (SIDS) comprise a group of 58 nations identified by the United Nations as facing unique sustainability challenges. These challenges include high exposure to climate change and a lack of data and limited resources. The effects of climate change are already observed in SIDS, notably an increase in the magnitude and frequency of natural disasters, biodiversity loss, ocean acidification, coral bleaching, sea-level rise, and coastal erosion. The coastal zone is considered to be the main economic, environmental, and cultural resource of SIDS, making them particularly vulnerable to the adverse effects of climate change. This project focuses on quantifying&#160;and disentangling coastal changes, including erosion, accretion and coastline stability. Existing literature lacks a comprehensive understanding of the patterns of coastal changes, as well as the main anthropogenic and environmental drivers involved. We&#160;address this research gap by quantifying the challenges that SIDS encounter, with a particular emphasis on coastal changes.The approach is data-driven, relying on observational time series extracted from remote sensing (e.g., Sentinel-2, Planet Scope, Landsat missions), in situ measurements (e.g., tide gauge data), and open-access databases. We have developed a robust method based on image segmentation to extract the island's shape over time, enabling us to illustrate the island's dynamics and obtain reliable time series of the coastline position.&#160;The main drivers of coastal changes are then identified and quantified using time series analysis methods, including causal inference and discovery methods, for SIDS worldwide. We place a specific focus on the Maldives (Indian Ocean) due to its low elevation and high human activity. Additionally, the methodology expands to investigate a spectrum of issues, including the impacts of human activities (e.g., land reclamation, sand mining, shoreline ar
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OtherKarmpadakis I, Bellos V, 2024,
Rogue wave occurrence over planar coastal bathymetries
<jats:p>Rogue waves have received considerable attention in recent years, with major advancements in their generation mechanisms having been defined. However, the focus of most investigations has been related to rogue wave occurrence in deep water. In contrast, far fewer results are available in shallower water depths. As such, the present work focuses on exploring the occurrence probabilities of rogue waves in coastal waters, as well as the physical mechanisms that lead to their formation. This is achieved by a thorough analysis of a very extensive experimental dataset of random waves propagating over planar beaches. More specifically, long simulations of realistic JONSWAP spectra arising in intermediate water depths have been generated at the deep end of the Coastal Flume at Imperial College London. These propagate over 3 uniform slopes with inclinations varying between 1:15 and 1:50, while being sampled by a dense array of wave gauges. The fine spatial resolution of wave gauges allows for a detailed description of large wave evolution as they travel towards the shoreline. Importantly, a parametric approach in defining the offshore forcing conditions has been adopted and covers a wide range of sea-state steepnesses and effective water depths. Taken together, 15 different storm conditions, each consisting of approximately 20,000 waves, have been considered for each bed slope configuration.In analysing these results, the occurrence of rogue waves is examined at all spatial locations across the coastal zone. We observe a considerable increase in rogue wave occurrence for reducing water depths which has not been found previously. This is particularly the case for moderately mild offshore storms. In exploring the shape of rogue waves arising at different water depth regimes, the relative importance of dispersion and nonlinearity is defined. While rogue waves arising at the deeper end of the coast resemble NewWave type events, solitary-type events become more pron
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OtherHorner G, Gryspeerdt E, 2024,
How does the lifetime of cirrus detrained from deep convection impact the cloud radiative effect of the tropics?
<jats:p>Large cirrus outflows detrained from deep convection play a vital role in modulating the radiative balance of the Earth&#8217;s atmosphere. The total cloud radiative effect (CRE) in the tropics is close to zero due to a cancellation between a large shortwave (SW) cooling from optically thick clouds and a longwave (LW) warming from high-altitude thin cirrus that spread over much of the tropics. Any small percentage changes to the LW or SW components of these large detrained cirrus in a future climate could, therefore, have significant impacts on the overall CRE in the tropics.A crucial question is how the lifetime of these detrained cirrus impacts the total cloud radiative effects in the tropics. Characterising the detrained cirrus outflows, how they evolve over time, and how they might change in a future climate is vital in order to understand their role in the climate system and to constrain past and future climate change.Building on the &#8216;Time Since Convection&#8217; product used in Horner &amp; Gryspeerdt (2023), this work investigates how the initial conditions of deep convection influence the radiative evolution and lifetime of the detrained cirrus. If we extend the lifetime of detrained cirrus, how does this change their total radiative effect and the radiative balance in the tropics? To answer this question, data from the DARDAR, ISCCP, and CERES products are used to build a composite picture of the radiative and microphysical properties of the clouds, which are investigated under varying initial conditions.It is found that the initial conditions of the convection, in particular whether the convection occurs over land or ocean, play an important role in determining the lifetime and total CRE of the detrained cirrus clouds, due to the strong diurnal contrasts in convection over ocean and land. Furthermore, it is found that artificially extending the lifetime of the detrained cirrus increases the total CRE of h
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OtherGryspeerdt E, Stettler M, Teoh R, et al., 2024,
Observing links between lifetimes of satellite detectable contrails and aircraft type
<jats:p>Clouds produced by aircraft (contrails) are responsible for over half of the positive radiative forcing from aviation, leading to the proposal of contrail avoidance as a method for mitigating the climate impact of aviation. This requires accurate prediction of the radiative properties of individual contrails, which themselves are highly dependent on the contrail microphysical properties, lifetime and macrophysical evolution along with the background atmospheric state. &#160;In-situ observations have also shown an impact of the generating aircraft and its fuel type on the properties and evolution of contrails. However, these observations are typically made close to the aircraft, with fewer observational constraints for the properties of the longer-lived contrails that drive the majority of the radiative forcing.Coupling satellite observations of contrails with flight data, we track contrails formed by individual aircraft over the North Atlantic. We find a strong link between aircraft type and contrail lifetime, with newer, more fuel-efficient aircraft forming longer-lived contrails. This relationship is not driven by the aircraft properties, but rather by operational differences in aircraft flight patterns, with the newer types flying higher in this region and so producing contrails with longer lifetimes. We present some encouraging initial evidence of reductions in aircraft soot emissions affecting contrail lifetime.</jats:p>
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OtherKing O, Matthews T, Andrade M, et al., 2024,
Establishing glacier proximal meteorological and glacier ablation stations in different climatic zones along the South American Andes.
<jats:p>Climate change has had a significant impact on the behaviour of the high mountain cryosphere, with widespread glacier retreat and mass loss now occurring in most of the planet&#8217;s glacierised mountain ranges over multi-decadal timescales. If we are to accurately understand the impacts of deglaciation on freshwater availability to communities downstream, robust modelling of future glacier meltwater yield is paramount. Meteorological observations at glacierised elevations are essential to drive simulations of the energy balance at glacier surfaces, and therefore glacier melt, although such records are sparse in most high mountain regions due to the logistical challenges associated with making even short-term measurements. The scarcity of high-altitude meteorological observations has resulted in only limited understanding of factors such as the spatial and temporal variability of temperature lapse rates, precipitation amounts and phase, and the prevalence of conditions suited to sublimation, all of which have an important influence on glacier mass loss rates at high elevation.Here we summarise the installation of meteorological and glacier ablation stations in different climatic zones of the South American Andes - the Tropical Andes of Peru (Nevado Ausangate basecamp, 4800 m, (13&#176;48'45.96"S, 71&#176;12'53.18"W) and Bolivia (Laguna Glaciar, 5300 m, 15&#176;50'10.59"S, 68&#176;33'11.30"W), the Subtropical Andes (Glaciar Universidad, Chile, 2540 m, 34&#176;43'10.07"S, 70&#176;20'44.98"W) and Patagonian Andes (Lago Tranquillo, Chile, 280 m, 46&#176;35'47.00"S, 72&#176;47'38.91"W) &#8211; as part of the NERC-funded Deplete and Retreat Project. Meteorological station records include time series of air temperature and pressure, relative humidity, wind speed and direction, incoming and outgoing short- and longwave radiation, precipitati
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OtherBuytaert W, 2024,
Building a community of practice to produce hydrological evidence: the iMHEA example
<jats:p>The IAHS HELPING decade aims to foster a stronger connection and interaction between scientists, practitioners, policy makers, and end-users towards the goal of global water security. This is a formidable challenge. Despite increasing and highly valuable efforts of scientists to reach out beyond their own discipline and working environment, the ultimate goal of co-creating actionable knowledge is still a long way off in most contexts. Establishing communities of practice has been posited as an approach to creating inter- and transdisciplinary environments that enable cross-learning, pooling of expertise, and collaborative working towards a common goal. However, establishing such communities of practice is very hard, and the conditions and driving factors that allow them to emerge and be productive are poorly understood. It is therefore informative to analyse existing case studies to gain a better understanding of how they can be created and made sustainable. Here I analyse the case of the Initiative for the Hydrological Monitoring of Andean Ecosystems (iMHEA), which is a grassroots initiative that emerged 15 years ago as a collaborative attempt to generate a solid scientific evidence base to support water management in the upper Andes.It started as a small network of 4 partners operating 6 catchments in Ecuador and Peru, using a common monitoring protocol. Since then, it has grown into a network of 22 partners, monitoring 51 catchments at 24 sites along the Andes. Partners represent academia, civil society, and local, regional, and national governments. Originally focused on sharing technical expertise, iMHEA has evolved into a more holistic knowledge co-creation community with a strong focus on community involvement, knowledge exchange, and supporting decision making at various levels.We attribute the success of iMHEA to several factors, of which we believe the following are key. The members&#8217; ability to raise funding, both at the start a
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