The North Atlantic Climate System Integrated Study

Lead Research Organisation: National Oceanography Centre
Department Name: Science and Technology


Major changes are occurring across the North Atlantic climate system: in ocean and atmosphere temperatures and circulation, in sea ice thickness and extent, and in key atmospheric constituents such as ozone, methane and particles known as aerosols. Many observed changes are unprecedented in instrumental records. Changes in the North Atlantic directly affect the UK's climate, weather and air quality, with major economic impacts on agriculture, fisheries, water, energy, transport and health. The North Atlantic also has global importance, since changes here drive changes in climate, hazardous weather and air quality further afield, such as in North America, Africa and Asia.

ACSIS is a 5 year strategic research programme that brings together and exploits a wide range of capabilities and expertise in the UK environmental science community. It's goal is to enhance the UK's capability to detect, attribute (i.e. explain the causes of) and predict changes in the North Atlantic Climate System. ACSIS will deliver new understanding of the NA climate system by integrating new and old observations of atmospheric physics and chemistry, of the ocean state and of Arctic Ice. The observations will be complemented by detailed data analysis and numerical simulations. Observations will come from existing networks, from NERC's own observational sites in the North Atlantic, and from space. Seasonal surveys using the NCAS FAAM aeroplane will further enhance our observational strategy. A key dimension of the observational opportunity is that data records of sufficient length, for multiple variables, are becoming available for the first time. The modelling component will involve core numerical simulations with cutting-edge atmosphere, ocean, sea ice, chemistry and aerosol models using the latest parameterizations and unprecedented spatial detail, as well as bespoke experiments to investigate specific time periods or to explore and explain particular observations.

ACSIS will provide advances in understanding and predicting changes in the NA climate system that can be exploited to assess the impact of these changes on the UK and other countries - for example in terms of the consequences for hazardous weather risk, the environment and businesses. ACSIS outputs will also inform policy on climate change adaptation and air quality.

Planned Impact

Policy makers: Advances in understanding the role of natural and anthropogenic drivers in North Atlantic climate change delivered by ACSIS will contribute to the next Intergovernmental Panel on Climate Change Assessment Report (AR6) and to national and international policy-making on climate change adaptation and mitigation. Improved understanding of the impact of stratospheric ozone change on tropospheric composition and climate will inform assessments for the Montreal Protocol. Advances in understanding the role of emissions, relative to other factors, in shaping UK air quality will benefit policy formulation in Defra. Representatives of relevant government departments will be invited to the Community Meetings that are a planned part of the programme. These meetings will include specific sessions on stakeholder needs.

The Met Office and its customers will benefit from the process-based evaluation of their models and forecast systems. Improvements in modelling and understanding will be exploited to improve the accuracy and reliability of climate forecasts and projections. This will happen efficiently through the co-delivery of ACSIS by Met Office and NERC scientists.

The EU Copernicus Climate Change Service will benefit from advances in observations, models, understanding and predictions of changes in the regional climate of the North Atlantic/European region. ACSIS partners are already directly engaged in the development of relevant services and this engagement will increase through the programme.

Businesses concerned with changing weather and weather-related risks will benefit from advances in understanding the drivers of changing risk. ACSIS partners have established collaborations with the insurance and energy industries in particular, and these collaborations will provide an important pathway for communication of ACSIS findings. These interactions will be enhanced internationally through related work in the EU PRIMAVERA programme, as well as through the Community Meetings mentioned above.

General public and the media. The observations of declining Arctic sea-ice have become an iconic symbol of our changing climate system for the media and the general public. The ACSIS Essential Climate Variables, presented in accessible form and updated regularly on the ACSIS website, will provide a similar but broader based snap-shot of how the climate system is changing in the UK's backyard. The presentation of multiple variables in a consistent format will provide an important regular opportunity for ACSIS scientists to discuss and explain the complex nature of changes in a way that is accessible and engaging. We anticipate a high level of media interest in this dimension of the programme.

ACSIS is specifically designed to enable as well as deliver research and as such there is a wide community of academic beneficiaries (see separate summary), who will themselves contribute to enhancing the overall impacts of the programme.


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Description We have investigated the record sea surface temperatures that have developed in the North Atlantic Ocean over the last two years (popularly known as the Big Blue Blob) and found that much of this can be related to the effect of the atmospheric circulation which was characterised by anomalously cold air and strong winds which cooled the ocean. We have also found evidence that the Blob, once it was formed, may have favoured the occurrence of the 2015 European heatwave by influencing the position and strength of the atmospheric jet stream.

A linked set of studies have focussed on understanding why there are large variations over one or more decades in the amount of heat which is stored in the subpolar North Atlantic Ocean as these variations have profound implications for the climate (temperatures and rainfall) of the UK and Europe. The three studies have been conceived and performed by researchers from NOC, BAS and NCAS.

We found that on decadal/multidecadal timescales, changes in the Atlantic ocean circulation, specifically the strength of vertical overturning are the main driver of ocean heat content in the Subpolar North Atlantic. Changes in the heat content of the western subpolar region (westwards of Cape Farewell, the tip of Greenland) always occur near the surface initially and only arrive at depth many years later. The penetration to deep levels happens mainly due to continuous downwelling and diffusion at the continental boundaries around Greenland and Labrador, contrary to the previous consensus that intermittent deep convection in the central Labrador Sea plays the dominant role in modifying deep ocean properties.

The long timescales uncovered suggest that the ocean heat content and to some extent the sea surface temperatures in the region could potentially be predicted several decades in advance provided the mechanisms involved are captured by forecast models (e.g. realistic representation of downwelling along the boundaries). We know from previous studies that the climate of UK, western and central Europe, West and North Africa and eastern North America are strongly affected by decadal variations in subpolar gyre heat content and SST so there could be great societal benefit from such predictions.

Our results were achieved by combining ocean observations of heat content going back to the 1950s, output from state of the art ocean only and climate model simulations. The work builds on two advanced diagnostic techniques: decomposition of temperature anomalies into a heave component which affects density and a spice component which does not; and use of an ocean adjoint model which allows one to compute the sensitivity of the heat content to earlier conditions and external forcing, such as air-sea heat fluxes or windstress. This work has therefore drawn on expertise across the ACSIS programme and would have been much more difficult to achieve if the ACSIS connections had not been in place

Going back to the shorter timescales, we have found that sometimes winter atmospheric conditions cool the North Atlantic Ocean more than normal and that the subsurface ocean then remains unusually cool for the whole of the subsequent summer. This extra cold subsurface water is then mixed back up to the surface by stormy weather the next winter and modifies the atmospheric weather systems so that less warm subtropical air is transported towards the British Isles and Western Europe resulting in an increased likelihood of a cold winter. This result could be of help in improving forecasts of winter weather on seasonal timescales.

We have also been monitoring the Atlantic Overturning Circulation since 2004. This circulation brings warm near-surface waters up from the tropics to the sub polar regions between Britain and Labrador and even further north to Norway, whilst bringing colder waters back southwards at great depths (greater than 1000m). We have found that the overturning has weakened substantially (by about 30%) since 2008 (i.e. for more than a decade) and it looks like it was more of a sudden shift rather than a slow trend. This means that currently, the ocean is delivering less heat the sub polar regions. We are exploring the implications for climate in these regions.
Exploitation Route Understanding the origin and fate of cold sea surface temperature anomalies in the atlantic might ultimately improve our forecasts of phenomena such as heatwaves and cold winters - with late societal benefit. On longer timescales, separating out the effects of short term (year-to-year) variations due to natural atmospheric variability will help to pin down and understand much longer term trends related to anthropogenic warming and to multidecadal variability of the ocean overturning circulation. Additionally on decadal timescales, there will be considerable societal benefit in being able to predict average sea surface temperature conditions (and associated climatic effects such as hurricane season intensity) over successive ten year (or longer) periods.
Sectors Agriculture, Food and Drink,Energy,Environment,Leisure Activities, including Sports, Recreation and Tourism

Description Some of the findings have been cited in the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. This has fed into a greater awareness of the severity and impacts of climate change on the part of both the general public and policymakers.
First Year Of Impact 2018
Sector Aerospace, Defence and Marine,Environment
Impact Types Societal,Policy & public services

Description Citation in the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate
Geographic Reach Multiple continents/international 
Policy Influence Type Citation in systematic reviews
Impact This report is part of the IPCc series of report and as such has helped to change public and government attitudes to climate change and its impacts. This report is expected to have substantial impacts on government policy in respect of climate change adaptation and mitigation policies, both nationally and internationally.
Description Reports for the Marine Climate Change Impacts Partnership
Geographic Reach National 
Policy Influence Type Citation in systematic reviews
Impact UK Businesses and Local Governments use the MCCIP Science Review for formulating and implementing adaptation policy with respect to climate change.
Description (Blue-Action) - Arctic Impact on Weather and Climate
Amount € 8,103,125 (EUR)
Funding ID 727852 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 12/2016 
End 02/2021
Description (COMFORT) - Our common future ocean in the Earth system - quantifying coupled cycles of carbon, oxygen, and nutrients for determining and achieving safe operating spaces with respect to tipping points
Amount € 8,482,147 (EUR)
Funding ID 820989 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 09/2019 
End 08/2023
Description Emergence of Climate Hazards
Amount £1,600,000 (GBP)
Funding ID NE/S004602/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 02/2019 
End 01/2022
Title Climate modelling with resolved ocean eddies 
Description We have developed a climate model with 25km resolution in the atmosphere and 1/12 degree resolution in the ocean - the latter is sufficient to resolve mesoscale eddies. This is the first time such a capability has been available to UK researchers and our model is one of a handful of such models worldwide. The new model simulates Earths climate with unprecedented fidelity and can be used to investigate a wider number of questions (regional effects of climate change without the need for downscaling, mechanisms and predictability of extreme weather and climate events and many more). The development of this capability keeps the UK at the cutting edge of climate science internationally. 
Type Of Material Improvements to research infrastructure 
Year Produced 2016 
Provided To Others? Yes  
Impact The development of this tool has resulted in a number of publications, published, submitted and in prep. Two published papers are referenced here: Hewitt, Helene T.; Roberts, Malcolm J.; Hyder, Pat; Graham, Tim; Rae, Jamie; Belcher, Stephen E.; Bourdallé-Badie, Romain; Copsey, Dan; Coward, Andrew; Guiavarch, Catherine; Harris, Chris; Hill, Richard; Hirschi, Joël J.-M.; Madec, Gurvan; Mizielinski, Matthew S.; Neininger, Erica; New, Adrian L.; Rioual, Jean-Christophe; Sinha, Bablu; Storkey, David; Shelly, Ann; Thorpe, Livia; Wood, Richard A.. 2016 The impact of resolving the Rossby radius at mid-latitudes in the ocean: results from a high-resolution version of the Met Office GC2 coupled model. Geoscientific Model Development, 9 (10). 3655-3670.10.5194/gmd-9-3655-2016 Roberts, Malcolm J.; Hewitt, Helene T.; Hyder, Pat; Ferreira, David; Josey, Simon A.; Mizielinski, Matthew; Shelly, Ann. 2016 Impact of ocean resolution on coupled air-sea fluxes and large-scale climate. Geophysical Research Letters, 43 (19). 10,430-10,438.10.1002/2016GL070559 
Title 1/12 degree ocean/25km atmosphere coupled historical climate simulation 
Description Output from a historical climate model simulation of unprecedented resolution, including fields such as ocean and atmosphere temperature, winds, ocean currents and a large number of other variables. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Impact Improved understanding of the influence of resolution climate variability, including the importance of including small scale processes such as mesoscale eddies in order to realistically model air-sea interaction on climate timescales. 
Title 1/4 degree historical forced ocean simulations 
Description Output from three ocean model simulations forced by different estimates of surface atmospheric conditions. Fields stored are monthly temperature, salinity, ocean currents and other fields for 1958-2007, 1958-2015 and 1958-2017 depending on the particular simulations. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? No  
Impact Understanding of the proximate cause of the observed variability (increase up to the mid 1990s, and then an ongoing decrease) of the Atlantic Meridional Overturning Circulation. This is being written up as a journal article. 
Title Simulations with the sea ice model CICE documenting the impact of improved sea ice physics 
Description Sea ice thickness data (CryoSat-2) have been used to identify and correct shortcomings in simulating winter ice growth in the widely used sea ice model CICE. Here, we provide the data from CICE simulations documenting the impact of improved sea ice physics and the sensitivity to forcing and initial data. Adding a model of snow drift and using a different scheme for calculating the ice conductivity improve model results. Sensitivity studies demonstrate that atmospheric winter conditions have little impact on winter ice growth, and the fate of Arctic summer sea ice is largely controlled by atmospheric conditions during the melting season. A full description of the data processing and uncertainties is given by Schröder et al. (2018), 'New insight from CryoSat-2 sea ice thickness for sea ice modelling', in The Cryosphere. All simulations are listed in Tables 1 to 3 of this paper. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Title Fast, Parallel intermediate complexity climate model (FORTE 2.0) 
Description This is a climate model with relatively low resolution (2.8 degrees in the atmosphere and 2 degrees in the ocean), but optimised for MP and open MP parallel processing so that it is fast enough to multicentennial and millennial climate simulations. It is easily configurable so that different continental and orographic/ocean bathymetry configurations can be explored. The model can be run with our without a stratosphere. There are basic thermodynamic sea ice and land soi/vegetationl models 
Type Of Technology Software 
Year Produced 2020 
Open Source License? Yes  
Impact As this has only just been released, we are expecting impacts to build up over time. 
Description ACSIS - OSNAP - RAPID meeting in Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact Talk about state of the art coupled ocean-atmosphere simulations to study the Atmospheric Response to the 2015 cold anomaly in the North Atlantic Ocean. The meeting was attended by 100+ international scientists
Year(s) Of Engagement Activity 2017