The ocean’s ability to store heat (uptake of 94% of the excess energy resulting from increased atmospheric concentration of greenhouse gases due to human activities) is much more efficient than that of the continents (2%), ice (2%) or the atmosphere (2%) (Figure 1; Bindoff et al., 2007; Rhein et al., 2013; Cheng et al., 2019). It thus has a moderating effect on climate and climate change. However, ocean uptake of the excess heat generated by an increase in atmospheric greenhouse gas concentrations causes marine waters to warm up, which, in turn, affects the ocean’s properties, dynamics, volume, and exchanges with the atmosphere (including rainfall cycle and extreme events) and marine ecosystem habitats. For a long time, discussions on climate change did not take the oceans into account, simply because we knew very little about them. However, our ability to understand and anticipate changes in the Earth’s climate depends on our detailed knowledge of the oceans and their relationship to the climate.
On our watery planet, the ocean is the primary regulator of global climate by continuous radiative, mechanical and gaseous exchanges with the atmosphere. In particular, the ocean absorbs, stores, and transports through its flow motion (i.e., currents) heat from the sun affecting atmospheric temperature and circulation around the world. Furthermore,seawater is the source of most precipitation. The ocean is much more efficient at storing heat (93% of the excess of energy resulting from the human induced Green House Gases content in the atmosphere) than the continents (3%) and the atmosphere (1%). As a result, the ocean is the slow component of the climate system and has a moderating effect onclimate changes. However, consequent to the continuous absorption by the ocean of the human induced excess of heat, ocean waters are warming, which has consequences on the ocean’s properties and dynamics, on its exchanges with the atmosphere and on the habitats of marine ecosystems. For a long time, discussions of climate change did not take the oceans fully into account, simply because there was very little knowledge about the latter. Nonetheless, our ability to understand and anticipate what might happen to Earth’s climate in the future, depends on our understanding of the role of the ocean in climate.
Ocean circulation plays a central role in regulating climate and supporting marine life by transporting heat, carbon, oxygen, and nutrients throughout the world’s ocean. As human-emitted greenhouse gases continue to accumulate in the atmosphere, the Meridional Overturning Circulation (MOC) plays an increasingly important role in sequestering anthropogenic heat and carbon into the deep ocean, thus modulating the course of climate change. Anthropogenic warming, in turn, can influence global ocean circulation through enhancing ocean stratification by warming and freshening the high latitude upper oceans, rendering it an integral part in understanding and predicting climate over the 21st century. The interactions between the MOC and climate are poorly understood and underscore the need for enhanced observations, improved process understanding, and proper model representation of ocean circulation on several spatial and temporal scales.