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

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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".