Chlorophyte "snow algae" and Streptophyte "glacier algae" are found across the cryosphere, forming widespread algal blooms in snowpacks and on glacier ice surfaces during spring/summer melt seasons. These blooms hold significant potential to exacerbate the already rapid loss of snowpack and glacial ice resources driven by climate change because they establish albedo feedbacks that amplify melt. Their presence also leads to the construction of active microbial food-webs that provide important ecosystem functions, e.g. carbon sequestration, nutrient cycling and export of resources to down-steam systems. The algae themselves are also important analogs for what life was like on Earth during past mass glaciations, and for how life may exist on other frozen planets across our solar system. Driven by these series of novelties, the snow and glacier algal research community has significantly expanded over recent years, with active projects now spanning Arctic, Alpine and Antarctic regions of the cryosphere. To-date, however, research projects have tended to work in isolation, employing different methods for the analysis of blooms. This has prevented comparisons of findings between regions of the cryosphere and an overall appreciation for the global role and impacts of blooms at present. In turn, we cannot yet project the fate of snow and glacier algal blooms into the future under climate change, or back to the past during key periods of Earth's history. Yet the critical mass achieved in the snow and glacier algal research community also presents an opportunity to pool knowledge and resources, and align methods to drive the field to new achievements. The CASP-ICE project brings together leaders in the field of snow and glacier algal research (x2 UK investigators and x12 international partners) to undertake the foundational work needed to align efforts across the research community and unlock the next generation of science on snow and glacier algal blooms cryosphere-wide. Specifically, we will tackle the following four major tasks: 1. Define consistent methods for sampling and mapping snow and glacier algal blooms within field sites, so that datasets produced into the future will be completely comparable across different regions and times of sampling. 2. Apply these methods in study sites that the CASP-ICE team are currently working to produce the first set of standardized samples and maps of blooms for the community to work with. 3. Undertake the nuts-and-bolts validation of both laboratory-based methods for analyzing field samples as well as computational methods for integrating field measurements and mapping datasets with larger-scale satellite imagery that is needed to monitor blooms at global scales. 4. Establish a list of field sites that can form the backbone of an ongoing cryospheric algal bloom monitoring network and secure the funding to continue monitoring into the future. CASP-ICE will achieve these tasks through a series of networking and knowledge exchange activities as well as hands-on science. An initial workshop in spring 2024 will provide the platform to define best practice methods for the community and start talks on future network structure and direction. All partners will then undertake sampling and sample/data analysis across their respective study regions to produce the first fully validated datasets on snow and glacier algal blooms across the cryosphere. The protocols defined and datasets produced will be leveraged in subsequent funding bids that will be prepared during a series of networking visits and partner meetings led by the project PI, providing the support needed for ongoing monitoring of blooms into the future as climate change proceeds. CASP-ICE will provide the network and scientific foundation needed to tackle the large-scale questions about the role of cryospheric algal blooms in the Earth System at present, into the future under climate change, and back into the past.

Depletion of the stratospheric ozone layer has been at the forefront of environmental concern over the last 40 years. The layer shields Earth's surface from certain wavelengths of harmful ultraviolet (UV) radiation that would otherwise be detrimental to human and plant health. Ozone also absorbs terrestrial infra-red (IR) radiation meaning it is a greenhouse gas, and changes in its abundance can therefore impact climate. The primary cause of ozone depletion is the release of halogens (chlorine and bromine) from long-lived anthropogenic compounds, such as chlorofluorocarbons (CFCs) and halons. Production of these ozone-depleting compounds is now controlled by the UN Montreal Protocol, but they were once widely used in refrigeration and fire suppression units, among other applications. Due to the success of the Protocol, the stratospheric abundance of chlorine and bromine is now declining, albeit slowly, and the ozone layer is widely expected to 'recover' to levels observed pre-1980 in the middle to latter half of this century. However, a key uncertainty, highlighted in the WMO/UNEP 2014 Assessment of Stratospheric Ozone Depletion, is the increasing emissions of uncontrolled chlorine-containing Very Short-Lived Substances (Cl-VSLS) which can also reach the stratosphere and cause ozone loss. The most abundant Cl-VSLS is dichloromethane (CH2Cl2), whose tropospheric abundance has increased by >60% over the last decade. CH2Cl2 is human-produced and in the Northern Hemisphere, close to industrial sources, long-term observations show a mean CH2Cl2 growth rate of ~8%/year. The precise cause of these increases is unknown. However, emissions of CH2Cl2 (and other Cl-VSLS) are known to be relatively large over Asia, and in the absence of policy controls on production, atmospheric concentrations are expected to continue to increase in coming years. Our recent modelling work has shown (i) that the contribution of Cl-VSLS to stratospheric chlorine has already doubled in the last decade alone, and (ii) that sustained CH2Cl2 growth could delay the recovery of the Antarctic Ozone Hole by up to several decades. This would significantly offset some of the gains achieved by the Montreal Protocol, and because the Ozone Hole influences surface climate of the Southern Hemisphere in several ways, could affect forward predictions of climate change. This project (ISHOC) establishes a new task force comprised of world-leading chemistry-climate modelling groups. We will perform the first concerted multi-model assessment of the threat posed to stratospheric ozone from CH2Cl2 growth. Lancaster University will lead the model intercomparison in collaboration with the University of Cambridge, and an international consortium of 9 partners. We will develop a series of growth scenarios describing possible future trajectories of CH2Cl2 in the atmosphere. Each of the models in our consortium will perform forward simulations considering these scenarios and the output will be analysed to determine (a) the expected delay to ozone recovery in different regions of the stratosphere due to CH2Cl2 growth and (b) the subsequent implications for climate and surface UV. The results from ISHOC will provide powerful new insight into the role of compounds not controlled by the Montreal Protocol in ozone depletion, which will be highly relevant to future international assessments of ozone and climate change (e.g. WMO/UNEP and IPCC reports). While the focus of ISHOC is on CH2Cl2, the task force will remain active beyond the project to examine future threats to ozone from other uncontrolled Cl-VSLS (e.g. CHCl3, C2H4Cl2) as they emerge. Indeed, our ongoing work suggests that emissions of these Cl-VSLS are also increasing.

We propose a network to stimulate new international collaboration in measuring and understanding the surface temperatures of Earth. This will involve experts specialising in different types of measurement of surface temperature, who do not usually meet. Our motivation is the need for better understanding of in situ measurements and satellite observations to quantify surface temperature as it changes from day to day, month to month. Knowing about surface temperature variations matters because these affect ecosystems and human life, and the interactions of the surface and the atmosphere. Surface temperature (ST) is also the main indicator of "global warming". Knowledge of ST for >150 years has been derived from in situ meteorological and oceanographic measurements. These have been fundamental to weather forecasting, to environmental sciences, and to detection and attribution of climate change. Thermal remote sensing of ST from space has a ~30 year history, including operational exploitation. Observations of high accuracy and stability come from the 20-year record of Along Track Scanning Radiometers (ATSRs) . ATSR-class capability will shortly become operational in the space segment of Global Monitoring for Environment and Security (GMES), and will continue until at least 2030. The best insight into ST variability and change through the 21st century will come from jointly using in situ and multi-platform satellite observations. There is a clear need and appetite to improve the interaction of scientists across the in-situ/satellite 'divide' and across all domains of Earth's surface. This will accelerate progress in improving the quality of individual observations and the mutual exploitation of different observing systems over a range of applications. Now is a critical time to initiate this research network. First, the network will link closely to a major new initiative to improve quantification of ST from surface meteorological stations (surfacetemperatures.org). Second, there are areas of acute need to improve understanding of ST: e.g., across regions of Africa, where in situ measurements are very sparse; and across the Arctic, where the evolving seasonal sea ice extent challenges the current practices for quantifying ST variability and change. Third, it is timely to share experience between remote sensing communities. All these motivations are present against a backdrop where ST is, in relation to climate change, of current public interest & relevance to policy. This network will increase the international impact of UK science. UK investigators are involved across the full scope of the proposed ST network, and have leading international roles in several areas. The network will ensure UK participation at the highest level across all domains of ST research. In this proposal, key world-class organisations overseas have roles in steering and/or hosting network activities. The network will welcome participation of others not contacted in preparation of this proposal. Permission will be sought from the originators of all data used for case studies to make the data set freely available. The network will be organised around three themes over three years: Year 1. In situ and satellite ST observations: challenges across Earth's domains Year 2: Quantifying surface temperature across Arctic Year 3: Joint exploitation of in situ and satellite surface temperatures in key land regions. The first theme is an inclusive question, designed to bring together research communities and develop a full picture of common research needs and aspirations. The second theme is a pressing research question to which the network will co-ordinate a useful and unique contribution. The third theme is one of long-term interest and importance in the strengthening of the observational foundations for climate change monitoring and diagnosis.

Humid heat is a serious risk to human health, reducing the body's ability to cool itself through sweating. The impact on humans will increase under climate change, particularly in tropical and sub-tropical 'hot spots', such as equatorial Africa and the Indian subcontinent, which are highly populated, and already very hot and humid. Whilst there is a growing body of research on dry-bulb temperature extremes, there is very limited understanding of the meteorological drivers of humid heat extremes, particularly the role of moisture transport, rainfall, and evaporation of moisture from the Earth's surface. In the context of humid heat extremes, the ability of weather and climate models to represent these processes and produce accurate weather forecasts and climate projections is largely unquantified. This is despite an urgency to adapt to and mitigate the impacts of globally increasing climate extremes. We will quantify the relative importance of different humid heat drivers on a cascade of scales, from local surface fluxes, to synoptic weather patterns, to the global-scale modes of tropical climate variability. We will map the specific locations (at the village or town scale) that have an increased risk of experiencing the highest maxima in humid heat during more widespread events that affect a larger region, under both current climate and possible future climates. We will quantify a possible emerging compound climate extreme: the co-occurrence of humid heat, heavy rainfall and flooding. The results will provide underpinning knowledge to improve the prediction of humid heat events, informing Early Warning System development and decision making across weather and climate change time-scales.

Rainfall is the climatic parameter of greatest importance to the populations of the tropical continents. The arrival of monsoon rains drives a rapid transformation of the landscape, allowing crops to grow and river networks to refill. Yet predicting where and when rain will fall in the tropics is a notoriously difficult problem. Progress has been made in predicting how remote ocean conditions, such as El Nino, can affect rainfall in different parts of the tropics. However local factors such as vegetation also play a role. For example, when tropical forests are cut down for agriculture, we have evidence that this affects rainfall both locally, and across neighbouring countries. Indeed, climate scientists have to take into account future deforestation rates as well as greenhouse gas emissions when they assess how tropical climate will change in the 21st century. Vegetation affects rainfall through the process of transpiration. When plants absorb carbon dioxide for photosynthesis, they lose water from their leaves. Trees are able to extract this water from several metres below the surface using their deep roots, allowing them to continue photosynthesising for months without rainfall. Crops and grasses on the other hand start to run out of soil water during dry spells, which reduces transpiration. Instead the solar radiation absorbed by the plant canopy raises the air temperature. Replacing forests with crops and grasslands changes the rates of moistening and heating of the atmosphere, particularly when the shallow-rooted species start to run out of soil water. These changes in turn affect the development of winds, cloud and rain. The details of how the atmosphere responds to vegetation is an area of significant scientific debate. Firstly, there is evidence that clearing patches of forest may increase rainfall over the cleared area and reduce it over the remaining forest, depending on the particular weather patterns. On the other hand, new results have shown that as air masses cross the continent, they pick up additional moisture from forests, which then leads to more rain several hundred kilometres further downwind. Finally, by controlling the balance between heating and moistening of the atmosphere, the vegetation can affect the winds bringing moist air off the ocean, delaying or extending the rainy seasons which characterise tropical climate. Although these 3 vegetation effects are each known to affect rainfall, we rely on computer models of the vegetation and atmosphere to understand how they might work in combination. Capturing the essential physical processes within a model is very challenging. In particular, there are large and long-standing uncertainties in the description of cumulonimbus storms (thunderstorms, which dominate the rainfall of many tropical regions) within the models. However through recent advances in computing power, we are now able to run these models for entire seasons with sufficient spatial detail to properly capture storms. In this project we will use data from satellites and the latest weather and climate models to get to the heart of how vegetation affects rainfall. Focusing on West Africa, one of the most climatically sensitive regions of the world, we will examine cloud and vegetation observations from the last 30 years to detect where deforestation has changed rainfall, and how the rapid greening of the savannah each year affects the monsoon rains. We will perform new computer simulations, incorporating the detailed development of thousands of individual storms, and examine what happens when we artificially deforest a region in the model. These results will allow us to assess the performance of the somewhat cruder models used to forecast climate change globally. By focusing on specific processes in the climate system, our results will help to improve these models, and at the same time provide robust conclusions on deforestation to guide land managers.