Asymmetries in ocean heat and carbon uptake, and effects on marine hazards

Lead Research Organisation: University of Liverpool
Department Name: Earth, Ocean and Ecological Sciences

Abstract

We need to understand what the future holds for the ocean, as more heat and carbon are supplied to the climate system. We know that the ocean is taking up over 90% of the extra heat supplied to the climate system and typically 25% of the extra carbon emitted to the climate system. We know that the ocean plays a central role in determining how global-mean surface warming is proportional to the cumulative amount of carbon emitted to the atmosphere. However, there are large uncertainties in this linear dependence of warming on carbon emissions. Reducing this uncertainty is an urgent task for climate science in order to reliably estimate the remaining carbon budget for specific warming targets, such as those set by the Paris Agreement.

Our work has demonstrated that the inter-model uncertainty in how surface warming relates to carbon emissions depends on the uncertainties in climate feedbacks involving clouds, ocean heat uptake and ocean carbon uptake. In order to gain understanding and to reduce the uncertainties, we need to identify the regional contributions to climate feedbacks, ocean heat and carbon uptake that make up the global response of the climate system.

How the regional ocean takes up the extra heat and carbon supplied to the climate system are also important in affecting the likelihood of marine hazards occurring, such as marine heatwaves and ocean acidifying events.
Accordingly, we need to know why some ocean regions are gaining the extra heat or carbon added to the climate system faster than other regions over the globe. We need to understand the drivers for this regional ocean heat and carbon uptake. These drivers range from
1. The extra heat and carbon supplied to the ocean is carried by a steady circulation over the global ocean, suggesting that the patterns of extra heat and carbon gain are similar in sign to each other;
2. The ocean drives changes in heat and carbon gain by time-varying changes in the circulation, suggesting that the patterns of extra heat and carbon gain may have opposing signs to each other;
3. The atmosphere drives changes in heat and carbon by differences in air-sea exchange, with cloud feedbacks acting to strengthen warm anomalies in the subtropics and weaken warm anomalies in the Southern Ocean.

We need to understand the drivers of these ocean heat and carbon anomalies as the resulting changes in the ocean environment affects the likelihood of marine hazards. For example, marine heatwaves are periods of enhanced temperature, lasting weeks to months, and their likelihood is affected by the regional pattern of how the ocean takes up the extra heat supplied to the climate system. The combination of temperature and carbon changes may alter the pH of the ocean leading to ocean acidifying events. We need to identify whether marine heatwaves and ocean acidifying events are likely to reinforce each other.

In conclusion, we will provide a new view of how anthropogenic heat and carbon anomalies are controlled, identifying their asymmetries, the ocean and atmospheric drivers, and implications for the global climate response and marine hazards.
This work is directly relevant to two Grand Challenges of the World Climate Research programme on "Clouds, circulation and climate sensitivity" and "Carbon feedbacks in the Climate system".

Planned Impact

Our aim is to inform the wider community about how surface warming from carbon emissions is controlled. We wish to engage with the following stakeholders:
1. Engagement with research stakeholders engaged in improving climate projections
We will engage with the research community in climate sciences through our publications and presentations in academic meetings.
(a) We will engage with climate scientists via our project partners from the Hadley Centre, namely Chris Jones (Head of the Earth System and Mitigation Science Team) and Doug Smith (Lead of Decadal Predictability).
(b) Two of our partners are lead authors of IPCC Chapters: Dr Chris Jones was a lead author for AR5 and Prof. Thomas Frölicher (Bern, Switz.) is a lead author of the next IPCC report.
(c) This proposal is directly relevant to the World Climate Research Programme Grand Challenge 'Carbon Feedbacks in the Climate System' --- Williams gave an invited keynote lecture on Ocean feedbacks at their workshop on 'Extending the Climate-Carbon Cycle Feedback Framework' at University of Bern on 25-27 April 2018.
(d) Williams and Frölicher will organise a joint workshop in Liverpool on the surface warming response to carbon emissions, including keynote talks from project partners.

2. Engagement with policy makers
The Grantham Institute has unparalleled expertise in communicating science to policy makers, which we will exploit to maximise impact. The institute has published a series of "briefing papers" (https://www.imperial.ac.uk/grantham/publications/briefing-papers/) aimed specifically at non-scientists, discussing climate science topics relevant to policy decisions in layman terms. We will contribute to this series by preparing a briefing paper on climate sensitivity, highlighting the roles of cloud feedbacks and ocean heat uptake. We expect a briefing paper on this topic to be of high interest in the context of the Paris Agreement targets and the increased climate sensitivity in CMIP6 climate mode.

3. Engagement with non experts, school children and the general public
We will also engage with non experts and the wider public through our own outreach linked to the Research Centre for Marine Sciences and Climate Change (www.liv.ac.uk/climate) and the new Centre for Coasts and Oceans (www.liverpool.ac.uk/liverpool-sustainable-coasts-and-oceans/, a new joint initiative between the University of Liverpool and the National Oceanography Centre).
For example, we provided a 'Briefing on the Science of Climate Change' on 10 February 2011 with 4 science talks (including from Williams), plus Sir David King, Andrew Miller MP and Lawrence McGinty to over 200 participants including Archbishop Carey of Liverpool, local MPs and councillors, and alumni.

4. Students, school children and those in the general public who wish to acquire a more informed view as to how changes in how climate change is occurring. In order to engage with the wider community, including school pupils, students, teachers and the general public, we have created a series Sea Level: A Liverpool View via You Tube (see OceanClimateAtUoL). We wish to extend this approach in developing 2 new animations:
(a) A scientific animation on "Cloud feedbacks and their relevance to climate sensitivity" (3 minutes long).
(b) To provoke a reaction we will display our scientific thoughts of the effects of climate change in a novel manner by developing a fantasy animation (4 minutes long) to capture the imagination of the public and especially school children, but melded with scientific understanding of climate projections. The theme will be "Venture into the Unknown - what would the Vikings have made of global warming?" We will construct an animation/cartoon to speculate on how the Viking exploration of North America might have been radically different with climate change, a warmer climate with no summer Arctic sea ice and the Northwest passage providing access to colonisation of the Pacific.

Publications

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