"Live fast, die young" famously describes the wild excesses of rock stars and Hollywood actors, but also encapsulates an important biological principle. Animals and plants that grow and reproduce quickly are more likely to be killed by natural enemies or environmental extremes. We usually explain this biological trade-off in terms of energy: more energy spent on growth means less energy invested in defence against enemies, the capture of essential resources, or into stores for surviving adverse conditions. A logical extension of this explanation is that, if the same growth could be achieved using less energy, more would be available for defence, resource capture and storage, thereby increasing survival. However, this prediction remains untested, despite its central importance for biology. The evolution of C4 photosynthesis in more than seventy plant lineages has increased the efficiency of photosynthetic energy conversion at high light and hot temperatures, in comparison with the ancestral C3 type of photosynthesis. To understand how this increase in photosynthetic efficiency influences growth, we have developed an experimental approach capable of comparing growth among hundreds of plant species in the same environmental conditions. We have discovered that, as well as a direct physiological effect of C4 photosynthesis in promoting faster growth, C4 leaves are unexpectedly less dense than C3 ones, further increasing growth efficiency. This allows C4 plants to be larger, with more growth invested in roots, which leads us to hypothesize that they may be able to accumulate greater storage, and have better access to water during drought than their C3 counterparts. Together, these hypothesized effects are expected to increase plant survival following repeated defoliation and drought events. If supported by experimental evidence, these ecological differences between C3 and C4 plants would have important global scale implications for the responses of plant communities to environmental change and land management. We propose to test these hypothesis using three large comparative experiments, capitalizing on our recent advances in developing high-throughput experimental screening methods. We are able to measure growth, allocation to roots verses shoots, storage and survival on thousands of plants in the same experimental set-up, and have developed novel statistical methods to analyze the large resultant datasets. We are also the first group to successfully apply metabolomic methods to identify and quantify storage compounds across multiple wild plant species. Our strategy for the proposed work will be to combine these approaches, investigating survival of experimentally imposed drought or repeated defoliation in seventy ecologically important grass species, representing seven independent evolutionary origins of C4 photosynthesis and their C3 sister taxa. Alternative hypothesized survival mechanisms will be tested by using plants of different ages to manipulate size. Since C4 photosynthesis also has a direct physiological effect on plant water use, by reducing stomatal aperture, we will make detailed measurements of plant hydraulics during the drought experiment. Findings from the three experiments will allow us to test the relative importance to survival of greater storage, deeper rooting, lower plant water use, and greater plant size in C4 then C4 species, and to gain a holistic understanding of the system. The work will enhance our mechanistic understanding of how a major physiological innovation changed growth-survival relationships and enabled plants to explore new phenotypic space. Throughout the project, we will work with mathematical modelers to ensure that the experiments will generate data that are useful for developing improved models of how global vegetation stores carbon and influences climate.

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.

A Mesoscale Convective System (MCS) is an organisation of many convective thunderstorms, each a few km in scale, into a coherent entity on scales of hundreds of km. We use the term to encompass a range of organised convective phenomena, including squall lines, supercells, and mesoscale convective complexes. MCS sit at the intersection between weather and climate. On weather timescales, these long-lived systems produce extreme precipitation and flash flooding. Through their coupling to the large-scale circulation, they play a key role in climate phenomena including the Madden Julian Oscillation (MJO), the Intertropical Convergence Zone (ITCZ), and the Monsoons. The dynamical coupling is two-way: large-scale environmental conditions dictate the likelihood of convective organisation occurring, while in turn the MCS strongly feedback on the dynamics and thermodynamics of the environment. Global numerical weather prediction (NWP) models, with grids of 15-20 km, and climate models, with grids of 50-100 km, cannot represent MCS. Our models operate in the "grey zone" where the phenomenon occurs at scales similar to the grid scale. This means that MCS are not fully resolved, but cannot be parametrised using conventional approaches, which assume that the unresolved process occurs on scales much smaller than the grid scale. Biases in the representation of the MJO, Asian Monsoons and ITCZ, as well as too few strong precipitation events, have been linked to deficiencies in the representation of MCS in models. Furthermore, "forecast busts" over the UK, for which the five- to six-day lead time forecast skill drops to around zero across the world's leading NWP centres, have been linked to a poor representation of MCS upstream over North America. We must improve the representation of MCS in weather and climate models. This project addresses the representation of MCS in the grey zone in a comprehensive and coordinated manner. We will first combine a new global satellite-derived database of MCS with analysis products to assess the predictability of MCS formation and evolution conditioned on the large scales, taking a novel, probabilistic approach. Secondly, several theoretical frameworks have recently been developed which describe the dynamical impact of MCS back onto the large scales. We will critically assess these frameworks, making innovative use of analysis increments from within the data assimilation cycle, to measure the upscale impacts of MCS that are missing from current models. We will use the fundamental understanding gained to develop a new parametrisation of the dynamical coupling between MCS and the larger scales. We will couple our approach to the new CoMorph convection scheme, which is undergoing trials for operational implementation in the UK Met Office's model. While CoMorph shows substantial improvements in initiating organisation, coupling of MCS to the large scales remains a problem. The representation we develop will be stochastic: we will represent the probability of different MCS tendencies conditioned on the resolved scale flow. Stochastic schemes are well suited to the grey zone, where parametrised motions are poorly constrained by the grid-scale variables, and so are very uncertain. Evaluating the new parametrisation will critically test the knowledge gained throughout the project. Having validated our knowledge, we will use the scheme to measure the importance of the dynamical impacts of MCS on climate phenomena including the ITCZ and the MJO. This project will produce a new understanding of the dynamics of MCS formation and upscale impacts. Through close collaboration with the Met Office, we intend to translate this into improved probabilistic forecasts for the UK and wider world. Only with reliable probabilistic forecasts can industry, policy makers, and the humanitarian sector quantify the risks of natural hazards, and act appropriately to protect against those hazards.