Not All Ocean Heat Transport Changes Are Created Equal
Lead Research Organisation:
University of Reading
Department Name: Meteorology
Abstract
Changes in Ocean Heat Transport (OHT) have been associated with changes in climate over the oceans and continents. Signals such as the Atlantic Multidecadal Oscillation (an oscillation of the averaged surface temperature in the North Atlantic ocean), which drives anomalously dry/wet conditions over European, are thought to be primarily generated by basin wide fluctuations in the Atlantic Overturning Circulation and associated OHT. At the core of the link between OHT and anomalous climate conditions is a chain of events: changes in OHT result in changes in the Ocean Heat Content (OHC) over a broad range of depths, which in turn modifies the Sea Surface Temperature (SST). It is ultimately through this SST modification that the OHT changes can influence the atmospheric circulation.
It has to be emphasized, however, that the OHT-OHC-SST chain is not systematic. In fact, it is likely that a large fraction of the OHT variability does only result in weak SST changes and thus little climate impact. Our current understanding of the link between OHT changes and climate variability is primarily based on statistical analyses of climate model simulations. Our proposal is that we need to understand better the mechanisms behind this link to be able to understand what the limited available observations can tell us about the ocean's impact on climate in real world, and whether or not our climate models are good approximations of the latter. Specifically, here are a few key questions that we wish to address: What makes an OHT change climatically important and potentially relevant to society? Is the OHT-OHC-SST chain properly represented in ocean and climate models? What are the implications for predictions of future climate change on the 1 to 10 year timescale of most relevance to many environmental policies of governments and businesses?
To address this, we propose to explore the ocean interior dynamics that constrains the OHT-OHC-SST chain and its representation in climate prediction systems. An important innovation of the project is a methodology to evaluate the potential climate impact of OHT changes, to be used to interpret decade-long observations of the Meridional Overturning Circulation and associated OHT changes by the UK funded RAPID project and its successors.
We will combine an analysis of subsurface ocean observations (Argo dataset) and ocean reanalysis products, a modeling approach with idealized models (to study physical processes) and realistic configurations (to link most readily with climate models and observations), and an evaluation of a global climate model and decadal prediction products.
Besides contributing to the success of UK-funded projects (like RAPID mentioned above, but also the upcoming OSNAP), this research will also benefit the UK community in terms of evaluation and potential improvements of the UK climate models and prediction systems (UKESM1/NEMO, Met Office DePreSys).
It has to be emphasized, however, that the OHT-OHC-SST chain is not systematic. In fact, it is likely that a large fraction of the OHT variability does only result in weak SST changes and thus little climate impact. Our current understanding of the link between OHT changes and climate variability is primarily based on statistical analyses of climate model simulations. Our proposal is that we need to understand better the mechanisms behind this link to be able to understand what the limited available observations can tell us about the ocean's impact on climate in real world, and whether or not our climate models are good approximations of the latter. Specifically, here are a few key questions that we wish to address: What makes an OHT change climatically important and potentially relevant to society? Is the OHT-OHC-SST chain properly represented in ocean and climate models? What are the implications for predictions of future climate change on the 1 to 10 year timescale of most relevance to many environmental policies of governments and businesses?
To address this, we propose to explore the ocean interior dynamics that constrains the OHT-OHC-SST chain and its representation in climate prediction systems. An important innovation of the project is a methodology to evaluate the potential climate impact of OHT changes, to be used to interpret decade-long observations of the Meridional Overturning Circulation and associated OHT changes by the UK funded RAPID project and its successors.
We will combine an analysis of subsurface ocean observations (Argo dataset) and ocean reanalysis products, a modeling approach with idealized models (to study physical processes) and realistic configurations (to link most readily with climate models and observations), and an evaluation of a global climate model and decadal prediction products.
Besides contributing to the success of UK-funded projects (like RAPID mentioned above, but also the upcoming OSNAP), this research will also benefit the UK community in terms of evaluation and potential improvements of the UK climate models and prediction systems (UKESM1/NEMO, Met Office DePreSys).
Planned Impact
Understanding the climate impact of Ocean Heat Transport (OHT) changes on interannual timescales is vital for our national interest, notably in the North Atlantic sector where changes in the Sea Surface Temperature (SST) have a direct influence on the European climate. The project will directly lead to significant advances in our ability to make robust decadal climate change predictions to inform decision-makers in government, business and society. The main beneficiaries of the work will be:
(i) Operational meteorological forecasting centres, in particular the Met Office: a component of the project is the evaluation and possible improvements of climate models, in particular with regard to the robustness of the simulations of the OHT-SST connection. The assessment of the NEMO simulations and the Met Office Decadal Prediction System (DePreSys) will be a very useful outcome for the users of NEMO and of coupled climate models which NEMO is part of, as well as users of the prediction system products.
(ii) Developers and end-users of ocean re-analysis products: As part of the project, we will evaluate ocean reanalysis products participating in the EU-funded MyOcean portal. This will lead to potential improvements for the next generation of products and ultimately benefit the numerous end-users of these products (see http://marine.copernicus.eu). An essential application of ocean reanalysis products is the initialization of decadal prediction systems and climate prediction systems, with numerous applications including the study of Ocean Heat Uptake, the so-called "Hiatus" problem, regional climate impacts, etc. As such, our results will benefit indirectly users of seasonal-to-decadal system predictions (see below).
(iii) UK Government departments, agencies, local authorities and advisory bodies involved with local, national and international policy concerning environmental issues and/or interconnected risks (e.g. infrastructure, agriculture, health, international development, etc): indirect benefit via improved decadal prediction. A number of these organizations directly use climate science evidence in building advice for the UK government on climate risks and in developing mitigation and adaptation strategies at national, European and international. Improved decadal climate predictions will be of direct relevance to positions taken by them. In addition, as UK prediction systems, from seasonal to decadal and longer timescales, are being unified around a core ocean modeling tool (NEMO), assessment of this ocean component will benefit a wide range of end-users, beyond those interested in decadal predictions.
(iv) The wider public: various benefits on different timescales, including opportunity to engage in climate change discussion on a timeframe of more tangible relevance to individuals than century-scale projections. One key channel for delivering this impact will be through the numerous outreach activities coordinated by the Department of Meteorology. These include opportunities to engage with students and teachers from all levels of education and provide them with exciting research material and a direct contact with cutting edge science.
Actions that will be implemented (see detailed description in Pathways to Impact):
- Organization of a workshop on the topic "OHT variability in climate"
- Dissemination of results to the Met Office and ECMWF through on-going collaborations,
- Communications of findings to the wider NEMO modelling community through the DRAKKAR meetings,
- Delivery of teaching material (lecture slides, movies) through a dedicated project website
- Presentations at schools and University open-days
- Contribution to the Grantham Institute briefing notes
(i) Operational meteorological forecasting centres, in particular the Met Office: a component of the project is the evaluation and possible improvements of climate models, in particular with regard to the robustness of the simulations of the OHT-SST connection. The assessment of the NEMO simulations and the Met Office Decadal Prediction System (DePreSys) will be a very useful outcome for the users of NEMO and of coupled climate models which NEMO is part of, as well as users of the prediction system products.
(ii) Developers and end-users of ocean re-analysis products: As part of the project, we will evaluate ocean reanalysis products participating in the EU-funded MyOcean portal. This will lead to potential improvements for the next generation of products and ultimately benefit the numerous end-users of these products (see http://marine.copernicus.eu). An essential application of ocean reanalysis products is the initialization of decadal prediction systems and climate prediction systems, with numerous applications including the study of Ocean Heat Uptake, the so-called "Hiatus" problem, regional climate impacts, etc. As such, our results will benefit indirectly users of seasonal-to-decadal system predictions (see below).
(iii) UK Government departments, agencies, local authorities and advisory bodies involved with local, national and international policy concerning environmental issues and/or interconnected risks (e.g. infrastructure, agriculture, health, international development, etc): indirect benefit via improved decadal prediction. A number of these organizations directly use climate science evidence in building advice for the UK government on climate risks and in developing mitigation and adaptation strategies at national, European and international. Improved decadal climate predictions will be of direct relevance to positions taken by them. In addition, as UK prediction systems, from seasonal to decadal and longer timescales, are being unified around a core ocean modeling tool (NEMO), assessment of this ocean component will benefit a wide range of end-users, beyond those interested in decadal predictions.
(iv) The wider public: various benefits on different timescales, including opportunity to engage in climate change discussion on a timeframe of more tangible relevance to individuals than century-scale projections. One key channel for delivering this impact will be through the numerous outreach activities coordinated by the Department of Meteorology. These include opportunities to engage with students and teachers from all levels of education and provide them with exciting research material and a direct contact with cutting edge science.
Actions that will be implemented (see detailed description in Pathways to Impact):
- Organization of a workshop on the topic "OHT variability in climate"
- Dissemination of results to the Met Office and ECMWF through on-going collaborations,
- Communications of findings to the wider NEMO modelling community through the DRAKKAR meetings,
- Delivery of teaching material (lecture slides, movies) through a dedicated project website
- Presentations at schools and University open-days
- Contribution to the Grantham Institute briefing notes
| Description | Improved understanding of limitations and advantages of a often-used method to analyze change in the heat that is stored in the ocean interior. This method separates changes due to the displacement of water masses from heat changes associated with the changes in the properties of water masses. This method is used in a number of research projects including NERC-funded research projects. Clarification of the biases and potentially misleading outcomes of this method will improve understanding and prediction of anthropogenic ocean heat uptake and climate change. A series of numerical simulations of the ocean where used to investigate how the ocean heat moves from the interior of the ocean to the surface. Once the heat is at the surface, it can be released to the atmosphere and influence weather and climate. The numerical simulation reveal the paths and time it takes for the heat to come up to the surface. In some cases, it takes years or decades for the heat to come to the surface. The release is often 1000s of km from the initial source of heat. This reveals a complex and delayed impact of the ocean on the atmosphere, but also the possibility of long term prediction if observations of ocean interior are significantly improved. |
| Exploitation Route | Numerous research projects aiming at predicting and analyzing ocean heat uptake associated with greenhouse gases emission employ the method. |
| Sectors | Environment |