Climate change is one of the most urgent issues facing humanity and life on Earth. Better predictions of future climate change are needed, so that measures to reduce its impact and cope with its effects can be put in place. However, improving these predictions requires better knowledge of how the global climate system functions, and this knowledge is currently incomplete. A critical gap concerns understanding of the uptake of heat and carbon by the oceans. Over 90% of the extra heat now present in the Earth System because of global warming has entered the ocean, with strong increases in both the upper and deep ocean apparent since the 1970s. Further, the global ocean is the largest reservoir of carbon in the climate system, and has absorbed nearly one-third of the extra carbon emissions produced since the industrial revolution. Climate change in the atmosphere is strongly moderated by these processes, and would be dramatically greater without them.

The Southern Ocean - the vast ocean that encircles Antarctica - is critically important in this regard. Because of the nature of its circulation, its physical and chemical properties, and its connections with the rest of the globe, it accounts for around half of the oceanic uptake of carbon, and around three-quarters of the heat uptake. However, because of its remoteness and hostile environment, with stormy seas, heavy sea ice in places, and long periods of darkness in winter, the Southern Ocean is also the least-measured and least-understood ocean in the world. One consequence of this lack of understanding is that the representations of the Southern Ocean in many of the models used to create future climate projections are not fit for purpose.

Our project, Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA), represents a linking together of many of the major environmental research institutes in the UK, who will work with national and international partners to address these issues. We propose a combination of data collection, novel analyses and computer simulations to radically improve our ability to measure, understand and predict the circulation and role in global climate of the Southern Ocean. Data collection will include major ship-based expeditions across the Atlantic sector of the Southern Ocean to determine the basin-scale transports of heat and carbon in all the different ocean layers (near-surface, intermediate, abyssal). It will include the use of novel technology and unmanned vehicles to collect data over much longer periods and much greater areas than ships alone could allow, and flights with research aircraft to determine climatically-important transfers of heat and carbon between the atmosphere and ocean in all different conditions of sea ice. Informed by the new understanding that these field campaigns will produce, improvements to ocean models will be proposed and tested, and the improvements delivered to climate modellers so that better future projections can be produced.

It is clear that these developments are required urgently - the benefits to be gained by improving climate prediction are difficult to overstate, with more effective strategies for dealing with climate change becoming feasible, and better planning assumptions made possible for industry, commerce and other sectors. The value of the Southern Ocean carbon sink was recently estimated to be in the trillions of dollars, but with uncertainty in the billions concerning how it will change in future: narrowing this uncertainty is thus a strong economic priority, as well as a scientific and societal one.

Potential Impact:
Societally, the benefits to be gained by improving climate prediction are difficult to overstate, with more effective adaptation and mitigation strategies becoming feasible, and industry, commerce and other sectors provided with a more robust planning framework. In economic terms, the capacity of the global ocean to absorb carbon was recently estimated to have an asset value of $4.3 trillion; the Southern Ocean currently accounts for around half of this absorption. The Southern Ocean also plays a key climatic role in removing anthropogenic heat from the atmosphere, however the present generation of ocean-only and coupled models all show unrealistic representations of key Southern Ocean processes, compromising our ability to predict future changes of the Earth System on time-scales from seasonal to centennial.

ORCHESTRA will advance our understanding of the mechanisms, rates and climatic impact of the drawdown of heat and carbon by the Southern Ocean and their subsequent transports to the rest of the globe, and it will generate impact via improvements in modelling capability to reduce uncertainty in global climate predictions, thus enabling economic benefit through energy and mitigation policy. The Met Office has been involved in all stages of the development of ORCHESTRA, ensuring that improvements to ocean and climate models will rapidly be made operational. Policy impact comes through the Intergovernmental Panel on Climate Change (IPCC) process that informs UK and global climate policy, and through our existing links with DECC (Shuckburgh). Analysis of the archive of climate model runs used by the IPCC (CMIP6) is part of ORCHESTRA and will inform the next IPCC Assessment Report. The model improvements undertaken during ORCHESTRA will feed into subsequent assessments, further narrowing the uncertainty range in climate projections. ORCHESTRA scientists have a strong track record of contribution to IPCC: as authors of assessment reports, by developing and analysing climate models used in the assessments, by making observations that constrain and inform climate models, and by publication of peer-reviewed literature that underpins the science of climate change.

Politically, our programme will help sustain UK leadership in climate science, important for underpinning Government-level climate change negotiations and important for UK geopolitical influence. Internationally, ORCHESTRA will raise the profile of excellent UK research into the ocean's role in climate. It will benefit (and leverage resource in-kind from) several international initiatives with whom we have partnerships, including the US Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program, the international Argo initiative, and GO-SHIP. This, and our interface with international climate database programmes, will ensure the widest uptake of NERC-funded data and science.

ORCHESTRA will enhance training opportunities for the next generation of UK leaders in environmental science. The institutes participating in ORCHESTRA are active in numerous NERC-funded Doctoral Training Partnerships (DTPs), and also the new NERC/EPSRC-funded Centre for Doctoral Training (CDT) in smart and autonomous systems. We will work with these networks, and generate new links to others across the UK, to provide fieldwork opportunities, infrastructure access and key datasets for doctoral candidate students.