Ocean Warming: From the Surface to the Deep in Observations and Models
The ocean is the primary heat sink of the global climate system. Since 1971, it has been responsible for storing more than 90% of the excess heat added to the Earth system by anthropogenic greenhouse-gas emissions. Adding this heat to the ocean contributes substantially to sea level rise and affects vital marine ecosystems. Considering the global ocean’s large role in ongoing climate variability and change, it is a good place to focus in order to understand what observed changes have occurred to date and, by using models, what future changes might arise under continued anthropogenic forcing of the climate system. While sparse measurement coverage leads to enhanced uncertainties with long-term historical estimates of change, modern measurements are beginning to provide the clearest picture yet of ongoing global ocean change. Observations show that the ocean is warming from the near-surface through to the abyss, a conclusion that is strengthened with each new analysis.
In this assessment, we revisit observation- and model-based estimates of ocean warming from the industrial era to the present and show a consistent, full-depth pattern of change over the observed record that is likely to continue at an ever-increasing pace if effective actions to reduce greenhouse-gas emissions are not taken.
Alongside the expanding observing capability, ocean reanalyses and the ocean component of climate models have considerably matured. The models and the improving forcing data sets that are used to reconstruct historical climate variability and change, used alongside observed reconstructions, provide a considerable toolkit to help tease apart the causes and effects of anthropogenic and natural forcing agents on ocean properties and drivers of long-term climate changes. Increases in model resolution will improve many aspects of ocean realism, such as the representation of the meridional overturning circulation and eddy processes (e.g., Griffies et al., 2015; Newsom et al., 2016), and improvements in model physics will make these toolkits even more useful. However, the increasing volume of data being collected will likely also create new challenges for analysis. These tools provide extremely valuable insights into how our future world will look and what will be the consequences of a strong societal response, or lack of response, to the climate change challenge.