Major challenges in urban governance concern interlinking food, water and energy systems, making these linkages understandable to all stakeholders (government, science, business, and citizens), and facilitating cooperation and knowledge exchange among them. The project titled "Creating Interfaces" will address these challenges by developing and testing innovative approaches for local knowledge co- creation and participation through Urban Living Labs in three mid-size cities on water: Tulcea, Romania, Wilmington, USA and Slupsk, Poland. Complemented by previous research and a citizen science toolbox, these Labs comprise a user-defined co-creative approach where research questions, problems, and solutions are decided and implemented with stakeholders themselves.

With the Kigali Amendment coming into force in 2019, the Montreal Protocol on Substances that Deplete the Ozone Layer has entered a major new phase in which the production and use of hydrofluorocarbons (HFCs) will be controlled in most major economies. This landmark achievement will enhance the Protocol's already-substantial benefits to climate, in addition to its success in protecting the ozone layer. However, recent scientific advances have shown that challenges lie ahead for the Montreal Protocol, due to the newly discovered production of ozone-depleting substances (ODS) thought to be phased-out, rapid growth of ozone-depleting compounds not controlled under the Protocol, and the potential for damaging impacts of halocarbon degradation products. This proposal tackles the most urgent scientific questions surrounding these challenges by combining state-of-the-art techniques in atmospheric measurements, laboratory experiments and advanced numerical modelling. We will: 1) significantly expand atmospheric measurement coverage to better understand the global distribution of halocarbon emissions and to identify previously unknown atmospheric trends, 2) combine industry models and atmospheric data to improve our understanding of the relationship between production (the quantity controlled under the Protocol), "banks" of halocarbons stored in buildings and products, and emissions to the atmosphere, 3) determine recent and likely future trends of unregulated, short-lived halocarbons, and implications for the timescale of recovery of the ozone layer, 4) explore the complex atmospheric chemistry of the newest generation of halocarbons and determine whether breakdown products have the potential to contribute to climate change or lead to unforeseen negative environmental consequences, 5) better quantify the influence of halocarbons on climate and refine the climate- and ozone-depletion-related metrics used to compare the effects of halocarbons in international agreements and in the design of possible mitigation strategies. This work will be carried out by a consortium of leaders in the field of halocarbon research, who have an extensive track record of contributing to Montreal Protocol bodies and the Intergovernmental Panel on Climate Change, ensuring lasting impact of the new developments that will be made.

Predictions of future climate, essential for safeguarding society and ecosystems, are underpinned by numerical models of the Earth system. These models are routinely tested against, and in many cases tuned towards, observations of the modern Earth system. However, the model predictions of the climate of the end of this century lie largely outside of this evaluation period, due to the projected future CO2 forcing being significantly greater than that seen in the observational record. Indeed, recent work reconstructing past CO2 has shown that the closest analogues to the 22nd century, in terms of CO2 concentration, are tens of millions of years ago, in 'Deep-Time'. The Palaeoclimate Modelling Intercomparison Project (PMIP) provides a framework (but no funding!) by which the palaeoclimate modelling community assesses state-of-the-art climate models relative to past climate data. Traditionally, PMIP has focussed on the relatively recent mid-Holocene (6,000 years ago) and Last Glacial Maximum (21,000 years ago), but these time periods have even lower CO2 than modern (~280 and ~180 ppmv respectively, c.f. ~400 ppmv for the modern). Recently, PMIP has expanded into other time periods, most notably the mid-Pliocene (3 million years ago), but even then, CO2 was most likely less than modern values (~380 ppmv). The modelling community would clearly benefit from an intercomparison of 'Deep-Time' climates, when CO2 levels were close to those predicted for the end of this century. We will organise and provide funding for 2 workshops, with the aim of producing papers describing the experimental design and outputs from a new climate Model Intercomparison Project - "DeepMIP", focussing on past climates in which atmospheric CO2 concentrations were similar to those projected for the end of this century. The papers will evaluate the models relative to past geological data, and aim to understand the reasons for the model-model differences and model-data (dis)agreements, providing information of relevance to the IPCC. A previous NERC grant, NE/K014757/1, is currently aiming to assess climate sensitivity (the response of surface air temperature to a doubling of atmospheric CO2), through geological time. That project is focussing on many time periods, but with only one model. This IOF will complement that project, and bring added-value, by focussing on one particular time period, but with many models. As such we will address the crucial issue of model-dependence.

Depletion of stratospheric ozone allows larger doses of harmful solar ultraviolet (UV) radiation to reach the surface leading to increases in skin cancer and cataracts in humans and other impacts, such as crop damage. Ozone also affects the Earth's radiation balance and, in particular, ozone depletion in the lower stratosphere (LS) exerts an important climate forcing. While most long-lived ozone-depleting substances (ODSs, e.g. chlorofluorocarbons, CFCs) are now controlled by the United Nations Montreal Protocol and their abundances are slowly declining, there remains significant uncertainty surrounding the rate of ozone layer recovery. Although signs of recovery have been detected in the upper stratosphere and the Antarctic, this is not the case for the lower stratosphere at middle and low latitudes. In fact, contrary to expectations, ozone in this extrapolar lower stratosphere has continued to decrease (by up to 5% since 1998). The reason(s) for this are not known, but suggested causes include changes in atmospheric dynamics or the increasing abundance of short-lived reactive iodine and chlorine species. We will investigate the causes of this ongoing depletion using comprehensive modelling studies and new targeted observations of the short-lived chlorine substances in the lower stratosphere. While the Montreal Protocol has controlled the production of long-lived ODSs, this is not the case for halogenated very short-lived substances (VSLS, lifetimes <6 months), based on the belief that they would not be abundant or persistent enough to have an impact. Recent observations suggest otherwise, with notable increases in the atmospheric abundance of several gases (CH2Cl2, CHCl3), due largely to growth in emissions from Asia. A major US aircraft campaign based in Japan in summer 2021 will provide important new information on how these emissions of short-lived species reach the stratosphere via the Asian Summer Monsoon (ASM). UEA will supplement the ACCLIP campaign by making targeted surface observations in Taiwan and Malaysia which will help to constrain chlorine emissions. The observations will be combined with detailed and comprehensive 3-D modelling studies at Leeds and Lancaster, who have world-leading expertise and tools for the study of atmospheric chlorine and iodine. The modelling will use an off-line chemical transport model (CTM), ideal for interpreting observations, and a coupled chemistry-climate model (CCM) which is needed to study chemical-dynamical feedbacks and for future projections. Novel observations on how gases are affected by gravitational separation will be used to test the modelled descriptions of variations in atmospheric circulation. The CTM will also be used in an 'inverse' mode to trace back the observations of anthropogenic VSLS to their geographical source regions. The models will be used to quantify the flux of short-lived chlorine and iodine species to the stratosphere and to determine their impact on lower stratospheric ozone trends. The impact of dynamical variability will be quantified using the CTM and the drivers of this determined using the CCM. The model results will be analysed using the same statistical models used to derive the decreasing trend in ozone from observations, including the Dynamical Linear Model (DLM). Overall, the results of the model experiments will be synthesised into an understanding of the ongoing decrease in lower stratospheric ozone. This information will then be used to make improved future projections of how ozone will evolve, which will feed through to the policy-making process (Montreal Protocol) with the collaboration of expert partners. The results of the project will provide important information for future international assessments e.g. WMO/UNEP and IPCC reports.

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.