This joint proposal to U.S. National Science Foundation's Directorate for Geosciences and U.K. Natural Environment Research Council aims to investigate how the Oyashio Extension frontal variability in the Northwest Pacific Ocean influences the large-scale atmospheric circulation by accumulating the interaction between the individual weather system and underlying ocean front. The atmospheric storm track exhibits the local maximum strength in the Northwest Pacific over the strong ocean fronts driven by collocated maximum baroclinicity, which is in turn maintained by huge heat and moisture supplied by the ocean. While significant advances have been achieved in the past decade or so on our understanding of ocean front's impact on the atmosphere for the mean climate, there are still many crucial questions yet to be answered, especially related to impact of ocean frontal variability on the atmospheric circulation variability. A particular goal of this proposal is to unveil the link between the local air-sea interaction in weather scale near the Oyashio Extension and its cumulative impact on the large-scale atmospheric circulation and climate variability. Specific emphases will be placed on the seasonality of this link by contrasting the early and late winter, and also the asymmetry/nonlinearity in the large-scale atmospheric response to warm and cold SST anomalies induced by a shift of the Oyashio Extension front to the north and south, respectively. These challenging goals will be addressed by combining analyses of observational and reanalysis datasets and targeted climate model experiments using the Variable Resolution Community Atmosphere Model v.6 with Spectral Element dynamical-core, a state-of-the art atmospheric general circulation model, which will be configured with a very high-resolution over the North Pacific and lower resolution elsewhere globally to realistically simulate the frontal air-sea interaction over the Oyashio Extension as well as the feedback with the large-scale circulation at a manageable computational cost. Furthermore, the role of local ocean coupling will be investigated by comparing the atmosphere-only simulations with those coupled to the 1-dimensional column ocean model.

Monsoon systems influence the water supply and livelihoods of over half of the world. Observations are too short to provide estimates of monsoon variability on the multi-year timescale relevant to the future or to identify the causes of change on this timescale. The credibility of future projections of monsoon behavior is limited by the large spread in the simulated magnitude of precipitation changes. Past climates provide an opportunity to overcome these problems. This project will use annually-resolved palaeoenvironmental records of climate variability over the past 6000 years from corals, molluscs, speleothems and tree rings, together with global climate-model simulations and high-resolution simulations of the Indian, African, East Asia and South American monsoons, to provide a better understanding of monsoon dynamics and interannual to multidecadal variability (IM). We will use the millennium before the pre-industrial era (850-1850 CE) as the reference climate and compare this with simulations of the mid- Holocene (MH, 6000 years ago) and transient simulations from 6000 year ago to ca 850 CE. We will provide a quantitative and comprehensive assessment of what aspects of monsoon variability are adequately represented by current models, using environmental modelling to simulate the observations. By linking modelling of past climates and future projections, we will assess the credibility of these projections and the likelihood of extreme events at decadal time scales. The project is organized around four themes: (1) the impact of external forcing and extratropical climates on intertropical convergence and the hydrological cycle in the tropics; (2) characterization of IM variability to determine the extent to which the stochastic component is modulated by external forcing or changes in mean climate; (3) the influence of local (vegetation, dust) and remote factors on the duration, intensity and pattern of the Indian, African and South American monsoons; and (4) the identification of palaeo-constraints that can be used to assess the reliability of future monsoon evolution.

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.

Our object is to understand how large, and how variable, are sources and sinks of greenhouse gases to the atmosphere from the North Atlantic. We aim to be able to describe how these have changed in the recent past and how they will change in the future under different climate scenarios. Most effort will be concentrated on carbon dioxide, and we will deliver a comprehensive budgeting of natural and anthropogenic components of the carbon cycle in the North Atlantic and understanding of why the air-sea fluxes of CO2 vary regionally, seasonally and multi-annually. Observations of CH4 and N2O and estimates of their regional fluxes will additionally be made. We, in collaboration with our partner institutions in Europe and the US, will undertake surface measurements of CO2 air-sea fluxes made from networks of voluntary observing ships and at fixed sites. These will be synthesised with observations from hydrographic sections of the interior carbon content. We will thus obtain accurate estimates of the uptake, present storage, and net transport of anthropogenic carbon, and variability in the natural uptake and release of atmospheric CO2 by the N. Atlantic. In parallel with direct estimates made from these observations, forward and inverse models (of both atmospheric and oceanic kinds) of these fluxes will be developed. The main hypotheses are (1) that past uptake and variability of CO2 in the region can be quantified by examination of the deep carbon inventory in the Atlantic, (2) that the present observed variability in CO2 uptake is due to a combination of biological and physical processes that are driven by climatic variations, the main factors being captured by ocean carbon simulations embedded in climate models, and (3) these variations (past, present and future) are due to a combination of variability internal to the climate system and external anthropogenic forcing - in proportions we will determine. Objectives are (1) a template for operational forecasting of the fluxes of GHGs into and out of the N. Atlantic, to be implemented as part of ICOS and in combination with ECMWF (2) an understanding of that sink that can be used to improve projections of how the ocean CO2 sink will change in the future, and (3) a quantitative understanding of how and why Atlantic Ocean uptake of anthropogenic CO2 has changed as a result of climate change over the last 100 years.

Microscopic organisms in the ocean called phytoplankton use the sun's energy to convert carbon dioxide (CO2), nutrients and water into organic matter, just as plants do on land. This organic matter is grazed upon by tiny animals called zooplankton that are found throughout the global ocean. Marine zooplankton are so abundant that the total weight of their global population greatly exceeds that of the ~8 billion humans alive on Earth today. Like all animals, zooplankton produce vast quantities of faecal matter that they eject into the surrounding environment. Some of this waste sinks down into the abyss, carrying with it carbon that was once in the atmosphere as CO2. Any faecal carbon that reaches the deep ocean may be locked away down there for 100's or even 1000's of years. The process of exporting carbon in this way occurs on such a scale that it plays a fundamental role in global climate regulation, keeping our planet cool by slowing the rate at which CO2 accumulates in our atmosphere. Zooplankton are cold-blooded, and as such, their physiological rates increase as their environment warms. By contrast, the body size of zooplankton decreases with warming, although the mechanism underlying this phenomenon remains uncertain. Indeed, there are many gaps in our understanding of how temperature affects zooplankton physiology. For example, does the rate at which they can capture food increase at the same rate at which their demand for energy increases with warming? If it does, perhaps they will simply eat their way out of the climate crisis? But what if it doesn't? Continued ocean warming may then result in zooplankton having to use more and more of their food to meet the temperature-driven increase in their energy demands, leaving less and less for growth and reproduction. Does this situation get worse if the amount of food available to zooplankton decreases with ocean warming? And do different sized individuals respond differently to temperature? Our incomplete understanding of the interplay between temperature, food supply and zooplankton body size means that we cannot reliably predict their response to ocean warming. Indeed, most global models of the ocean ecosystem that are used to help predict future climate assume that these aspects of zooplankton physiology are fixed, with no sensitivity to warming. We therefore have only limited confidence in our ability to forecast how the zooplankton contribution to global climate regulation via ocean carbon storage will change as the ocean warms throughout the 21st century. Our project, C-QWIZ, will determine how zooplankton of different sizes respond to increasing temperatures at different levels of food. In doing so, we will fill many of the knowledge gaps in our fundamental understanding of their physiological response to climate change. The C-QWIZ team is uniquely placed to translate this new understanding into existing mathematical models of the global ocean ecosystem; we will be the first to mechanistically assess how global warming affects zooplankton-mediated ocean carbon storage throughout the 21st century. Our chosen model is used by scientists around the world to forecast how Earth's future climate will change. These forecasts are used by politicians and policy makers to decide on how best to manage the future of our planet. Improving these models therefore ensures that our science delivers real and lasting change for the benefit of all society.