Using Ocean Heat and Carbon Timeseries to Understand the Relationship Between Emissions and Warming – a Case Study with the Subtropical North Atlantic

Climate models have an emergent near-linear proportionality between cumulative emissions and average surface warming, known as the climate metric TCRE. This metric is strongly affected by the oceanic uptake of heat and carbon. As such, ocean observations can provide an additional constraint on the TCRE, and understanding the evolution of ocean heat and carbon may help explain the evolution of the TCRE. We aim to explore how the ocean impacts the TCRE by examining historical time series of ocean heat and carbon and comparing them to CMIP6 models.

We use the Bermuda Atlantic Time Series (BATS) as a case study, as BATS has one of the longest-running ocean carbon time series. By augmenting the BATS hydrographic measurements with GLODAP data, we can create a multidecadal record of subtropical Atlantic carbon and heat with depth. Between August 1997 and August 2016, where global temperatures rose by 0.4°C, we find a thermocline heat content increase of 3.5 x 10⁵ J/m² and a carbon increase of 12 molC/m². We explore the trends in heat and carbon through the two decades and compare the measured response to the local response within a suite of Earth System Models. From there we identify how representative local ocean heat and carbon changes are for the TCRE and the extent that the TCRE can be diagnosed from these ocean timeseries.