Mechanistic controls of surface warming by ocean heat and carbon uptake

We are all aware of how carbon emissions are leading to concern about a warming of the planet. In our view, the climate response to carbon emissions can be divided into the following stages:
1. Past and on going increases in atmospheric CO2 are leading to a global warming of up to 0.6C over the last 50 years. The regional variability is though much larger than this global signal.
2. Continuing emissions are increasing atmospheric CO2 and driving a heat flux into the ocean, leading to ocean warming. The amount of warming is sensitive to the carbon emission scenario, as well as the rate of carbon uptake by the ocean and terrestrial system.
3. The regional distribution of warming and carbon drawdown is sensitive to how the ocean interior takes up heat and carbon, involving the transfer of surface properties into the thermocline and deep ocean.
4. In the future, after emissions cease may be after many hundreds of years, the atmosphere and ocean will approach an equilibrium with each other. At this point, the final atmospheric CO2 and the amount of climate warming is simply related to cumulative sum of all the previously carbon emitted.

One of the key findings of the latest IPCC report is how climate model projections suggest that global warming varies nearly linearly with cumulative carbon emissions. This response is not fully explained or understood, in terms of the essential underlying mechanisms or why different climate models reveal a different amount of warming to each other.

We have established a new theory to explain how surface warming varies in time with carbon emissions.
The aim of the proposal is to investigate the climate warming in the following manner:
(i) apply our new theory of how surface warming compares to cumulative carbon emissions, modified from an equilibrium response by the transient uptake of heat and carbon by the ocean and terrestrial systems;
(ii) conduct diagnostics of how the ocean is taking up heat, examining how the ocean is ventilated in terms of volumetric changes in ocean density classes;
(iii) develop ocean ventilation experiments with a range of ocean and climate models on timescales of decades to a thousand years, designed to explore the extent that the ocean uptake of heat and carbon are similar to each other, and assess their partly compensating effects on how surface warming links to carbon emissions;
(iv) compare with and analyse diagnostics of state of the art climate models, integrated for a century, including climate models driven by emissions, terrestrial uptake of heat and carbon, and radiative forcing from non-CO2 greenhouse gases and aerosols.

Our new theoretical framework has the potential to provide
(i) improved understanding of the mechanisms controlling the relationship between surface warming and carbon emissions, particularly focusing on the role of the ocean;
(ii) traceability between different ocean and climate models, identifying clearly which factors are leading to different climate responses;
(iii) reconcile Earth System model investigations over a wider parameter regime with IPCC class climate models.

This study is relevant for policy makers interested in different energy policies, and a link to end users is provided via the collaboration with the Hadley Centre and NOAA GFDL.

The study emphases the importance of engaging with the wider public by developing 4 targeted short and accessible videos on the climate problem, emphasising our new viewpoint.

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. Students, school children and those in the general public who wish to acquire a more informed view as to how changes in ocean warming and sea level rise are dependant on carbon emissions.
2. The ocean research community through our publications and presentations in academic meetings.
We will organise an end of programme workshop to be held in Liverpool with our project partners Drs Richard Wood, Jason Lowe and Ben Booth from the Hadley Centre, and Bob Hallberg and John Krasting from NOAA GFDL.
3. Wider scientific community interested in climate change. We have been invited by Cambridge University Press to write an accessible review of our new theory in a new online Elements series (www.cambridge.org/gb/academic/cambridge-elements), which are designed to provide original and concise reviews of work within the sciences and humanities.
4. Policy makers, civic leaders and the wider public through our own research activities linked to the Research Centre for Marine Sciences (www.liv.ac.uk/climate) and Living with Environmental Change (see short film, www.liv.ac.uk/research/research-themes/living-with-environmental-change/about/) research theme from the University of Liverpool; Williams is the Director of the Research Centre and one of the four University Champions for the latter theme.

In order to engage with the wider community, including school pupils, students, teachers and the general public, we want to create a series of short accessible videos (each approx. 3 minutes long) - combinations of film and animations with commentaries - to explain the key processes involved over both short and long term timescales. We have already followed this approach by providing a series Sea Level: A Liverpool View via You Tube (OceanClimateatUoL), which provides personal, historical and future perspectives on sea level and climate change drawing upon the unique history of engagement at Liverpool.

The new series will be made up of 4 short videos:
Video 1. If we emit carbon, what is the response? This video will be an introduction to the problem the research poses. We will explain the vocabulary we will use e.g. radiation, heat and warming and demonstrate how these ideas are linked.
Video 2. What is the long term response? We assume that after many centuries the atmosphere and ocean approach a global equilibrium in terms of heat and carbon transfer; draws on the relationship derived in Williams et al. [2012] GRL.
Video 3. What is the short term response? This video will discuss how atmospheric heat and carbon are taken up by the ocean; draws on the relationship derived by Goodwin et al. [2015] Nature Geoscience.
Video 4. What are the additional uncertainties? We will discuss how there is much more complexity in the real climate system. We will illustrate radiative forcing from other greenhouse gases, such as methane, and partial offsets by aerosols and cloud cover; draws upon advice from program partners at the Hadley Centre.

Distribution: the video outputs will be distributed via YouTube and through our websites, including the Research Centre for Marine Sciences and Climate Change and the National Oceanography Centre website.

We have used similar media to disseminate our research highlights to civic leaders, such as a 'Briefing on the Science of Climate Change' on 10 February 2011 to over 200 participants including Archbishop Kelly of Liverpool, local MPs and councillors, and alumni; see webcasts at www.liv.ac.uk/events/science-of-climate-change/. Other high-profile briefings were to Professor Tom Stocker (co-Chair of the next IPCC report) on 13 December 2011, to Lord Marland and Bishop James, 16 June 2011; and to Archbishop Kelly on 10 March 2010.