Ships generally burn low quality fuel and emit large quantities of sulfur dioxide and particulates, or aerosols (harmful at high concentrations), into the atmosphere above the ocean. In the presence of clouds the sulfur dioxide is rapidly converted into more particle mass growing them to sizes where they act as sites for cloud droplet formation. Given that about 70% of shipping activities occur within 400 km of the coast, ships are a large source of air pollution in coastal regions, causing 400k premature mortalities per year globally. In the UK, air pollution (including ship emissions) is responsible for 40,000 premature mortalities each year. In an effort to reduce air pollution from shipping activity, the United Nation's International Maritime Organization (IMO) is introducing new regulations from January 2020 that will require ships in international waters to reduce their maximum sulfur emissions from 3.5% by mass of fuel to 0.5%. Particulates emitted by ships may enhance the number of cloud droplets and potentially form regions of brighter clouds known as ship tracks. Largely because of this effect, some global models predict that ship emissions of particulates currently have a significant cooling influence on the global climate, masking a fraction of the warming caused by greenhouse gas emissions. So whilst a reduction in ship sulfur emission is predicted to almost halve the number of premature deaths globally via a reduction in sulfate aerosols, a lack of similar reductions in greenhouse gases from shipping (e.g. CO2) could lead to an overall climate warming. However, the magnitude of the cooling caused by particulates is very uncertain, with large discrepancies between global model and satellite-based estimates. This may be due to imprecise representations of the effects of aerosols on clouds in global models or biases in satellite detections of ship tracks. Furthermore, how shipping companies respond to the 2020 regulation (i.e. degree and method of compliance), in international waters where surveillance is challenging, is largely unknown and requires observational verification. We will take advantage of this unique and drastic "inverse geoengineering" event in 2020. By combining aircraft observations, long-term surface observations, satellite remote sensing, and process-level modelling, we will investigate the impact of the 2020 ship sulfur emission regulation on atmospheric composition, radiative forcing and climate in the North Atlantic. Results of this project will improve our understanding of the impact of ship emissions on air quality and climate.

The SPLICE project (Structure, Photosynthesis and Light In Canopy Environments) seeks to improve our understanding of global photosynthesis and hence our ability to model climate change, by considering the way in which the three-dimensional structure of plants interacts with light and how this in turn impacts on the uptake of carbon. We will employ state-of-the-art techniques to measure the three dimensional structure and photosynthesis of forests and construct detailed computer simulations to create a virtual laboratory that we can use to improve simulations from climate models. The process of photosynthesis is fundamental to life on Earth. In this project we are concerned with its role in the terrestrial carbon cycle, which in turn is important for understanding climate change. The land surface absorbs around 25% of anthropogenic CO2 emissions and this proportion has remained remarkably constant despite increasing emissions. Whether or not this will continue is unknown. Earth System Models (ESMs), which are essentially climate models that include climate-relevant biological process, include the uptake of carbon by plants via photosynthesis so that they can model (a) the influence of this process on atmospheric carbon dioxide concentrations and (b) the impact of climate change on global vegetation. There have been significant advances made in the modelling of photosynthesis inside these models in recent decades, for example the interaction with the nitrogen cycle, but they still include some very simple assumptions. We argue that chief amongst these is the way in which the three dimensional structure of vegetation is represented - something that has not been improved for nearly four decades. The equations in ESMs that govern the interception of light by plants, which in turn drives photosynthesis, make the simplifying assumption that leaves are randomly arranged in space, not clustered into tree crowns or around branches. This allows relevant equations in physics to be solved in such a way that results in computationally efficient computer code, but does not represent reality very closely. Recent research from the University of Reading has shown that the impact of including even a simple representation of these effects into an ESM can have large impacts on the global carbon cycle. In particular we showed an enhancement in the modelled estimates of global photosynthesis of 5 billion tonnes of carbon per year, or more than half of CO2 released from burning fossil fuels. Most of this occurs in the tropics, an area of the Earth likely to be especially vulnerable to the impacts of climate change. SPLICE will measure the 3D structure of 26 forests around the world using a combination of terrestrial Lidar scanning and airborne Lidar surveys. Lidar uses scattered laser light to infer structure of forests and information from it can be used to reconstruct a branch-by-branch simulation of the forest. We will take these data and build detailed 3D models of the forest light environment and resulting photosynthesis. The photosynthetic flux will be measured using a variety of techniques, including observations of solar induced fluorescence (SIF) from drones. These observations will be used to test our 3D models. SIF occurs as part of photosynthesis and although it has been known about for some time the technology to observe it remotely is relatively new. It provides a close proxy for the amount of carbon being taken up by photosynthesis. Our final step will be to use the detailed 3D models to develop a modified version of the computer codes used in ESMs to represent the interaction of light with vegetation canopies. These modified codes will be used in the land surface component of UKESM - the UK's new Earth System Model - to assess the impact of these changes globally and the magnitude of their impact on the carbon cycle and hence climate change.

Land-use and agriculture are responsible for around one quarter of all human greenhouse gas (GHG) emissions. While some of the activities that contribute to these emissions, such as deforestation, are readily observable, others are not. It is now recognised that freshwater ecosystems are active components of the global carbon cycle; rivers and lakes process the organic matter and nutrients they receive from their catchments, emit carbon dioxide (CO2) and methane to the atmosphere, sequester CO2 through aquatic primary production, and bury carbon in their sediments. Human activities such as nutrient and organic matter pollution from agriculture and urban wastewater, modification of drainage networks, and the widespread creation of new water bodies, from farm ponds to hydro-electric and water supply reservoirs, have greatly modified natural aquatic biogeochemical processes. In some inland waters, this has led to large GHG emissions to the atmosphere. However these emissions are highly variable in time and space, occur via a range of pathways, and are consequently exceptionally hard to measure on the temporal and spatial scales required. Advances in technology, including high-frequency monitoring systems, autonomous boat-mounted sensors and novel, low-cost automated systems that can be operated remotely across multiple locations, now offer the potential to capture these important but poorly understood emissions. In the GHG-Aqua project we will establish an integrated, UK-wide system for measuring aquatic GHG emissions, combining a core of highly instrumented 'Sentinel' sites with a distributed, community-run network of low-cost sensor systems deployed across UK inland waters to measure emissions from rivers, lakes, ponds, canals and reservoirs across gradients of human disturbance. A mobile instrument suite will enable detailed campaign-based assessment of vertical and spatial variations in fluxes and underlying processes. This globally unique and highly integrated measurement system will transform our capability to quantify aquatic GHG emissions from inland waters. With the support of a large community of researchers it will help to make the UK a world-leader in the field, and will facilitate future national and international scientific research to understand the role of natural and constructed waterbodies as active zones of carbon cycling, and sources and sinks for GHGs. We will work with government to include these fluxes in the UK's national emissions inventory; with the water industry to support their operational climate change mitigation targets; and with charities, agencies and others engaged in protecting and restoring freshwater environments to ensure that the climate change mitigation benefits of their activities can be captured, reported and sustained through effectively targeted investment.

By modifying the amount of solar radiation absorbed at the land surface, bright snow and dark forests have strong influences on weather and climate; either a decrease in snow cover or an increase in forest cover, which shades underlying snow, increases the absorption of radiation and warms the overlying air. Computer models for weather forecasting and climate prediction thus have to take these effects into account by calculating the changing mass of snow on the ground and interactions of radiation with forest canopies. Such models generally have coarse resolutions ranging from kilometres to hundreds of kilometres. Forest cover cannot be expected to be continuous over such large distances; instead, northern landscapes are mosaics of evergreen and deciduous forests, clearings, bogs and lakes. Snow can be removed from open areas by wind, shaded by surrounding vegetation or sublimated from forest canopies without ever reaching the ground, and these processes which influence patterns of snow cover depend on the size of the openings, the structure of the vegetation and weather conditions. Snow itself influences patterns of vegetation cover by supplying water, insulating plants and soil from cold winter temperatures and storing nutrients. The aim of this project is to develop better methods for representing interactions between snow, vegetation and the atmosphere in models that, for practical applications, cannot resolve important scales in the patterns of these interactions. We will gather information on distributions of snow, vegetation and radiation during two field experiments at sites in the arctic: one in Sweden and the other in Finland. These sites have been chosen because they have long records of weather and snow conditions, easy access, good maps of vegetation cover from satellites and aircraft and landscapes ranging from sparse deciduous forests to dense coniferous forests that are typical of much larger areas. Using 28 radiometers, and moving them several times during the course of each experiment, will allow us to measure the highly variable patterns of radiation at the snow surface in forests. Information from the field experiments will be used in developing and testing a range of models. To reach the scales of interest, we will begin with a model that explicitly resolves individual trees and work up through models with progressively coarser resolutions, testing the models at each stage against each other and in comparison with observations. The ultimate objective is a model that will be better able to make use of landscape information in predicting the absorption of radiation at the surface and the accumulation and melt of snow. We will work in close consultation with project partners at climate modelling and forecasting centres to ensure that our activities are directed towards outcomes that will meet their requirements.

Antarctica is changing. In February 2022, sea ice around Antarctica reached the lowest area that has been observed since satellite records began in 1979. This marks the first time that the area of sea ice ice has been observed to shrink below 2 million square kilometres. Compared to the average minimum, the 2022 February minimum is missing an area of sea ice that is about three and a half times the size of the UK. Directly following on from the sea ice minimum, in March 2022 record air temperatures were recorded across much of East Antarctica, with some meteorological stations observing temperatures 40C warmer than normal. These unprecedented conditions were associated with a very intense 'atmospheric river', a narrow corridor of warm water vapour, bringing warm air and moisture to the high Antarctic Plateau. We do not know whether these extreme regional climatic events are just 'one offs', and highly unlikely to occur again, or whether they are an indication of how Antarctic climate will develop in the future. These recent extreme weather events and conditions in Antarctica have prompted fresh concern about how climate change in this remote region will impact Earth. The protection of coastlines around the world from the future rise in sea level from Antarctica requires a better understanding of how the weather of Antarctica will evolve over the coming century. Any loss of Antarctic ice mass as a result of weather changes may raise the sea level around the globe. SURFEIT will thus investigate how changing snow and radiation, or surface fluxes, over the coming century will affect Antarctic snow and ice. The international SURFEIT team will: (i) improve how polar clouds are represented in our climate models; (ii) use pre-existing, and new, observations alongside climate model output to help improve our understanding of changes in snowfall over Antarctica; (iii) ensure we can accurately predict small-scale and extreme-event weather changes; and (iv) improve how we link our earth and ice system model components together, so that we can make better predictions of when Antarctic ice may fracture, and so raise global sea level. Our work on improving snowfall and ice predictions will help us answer our overarching question 'How will changes in Antarctic surface fluxes impact global sea-level to 2100 and beyond?'