Global ocean heat uptake (OHU) is an essential metric of anthropogenic climate change. A new approach to estimate the global OHU is to propagate its surface boundary conditions (BCs) downward using a Green's function (GF) representation of ocean transports. We present a new GF OHU estimate based on: a) observational GFs inferred from ocean tracers and b) new OHU BCs that improve on the sea surface temperature BCs. Our result not only provides an independent check of in-situ OHU estimates, but also extends the OHU record back to 1870. The new GF estimate agrees well with in-situ estimates for the global OHU rate during the well-observed period; especially, it removes a cold bias in the GF estimate of Zanna et al. (10.1073/pnas.1808838115). Importantly, the new estimate reveals an early acceleration of the global OHU rate during 1910–1940 (-0.13±0.08 → 0.41±0.09 W m-2), which is comparable to the recent acceleration since 1970 (0.14±0.13 → 0.56±0.09 W m-2). Regionally, the new GF estimate isolates the part of ocean warming that originates from the surface (excess heat); this component exhibits a bimodal distribution across latitudes with peaks at 30–40°N/S. Over 80% of the global OHU is a response to the OHU BCs poleward of 40°N/S, suggesting a high-latitude origin of ocean warming.
Quran Wu is a postdoctoral research associate working with Prof. Jonathan Gregory at University of Reading. His recent work focuses on constraining estimates of ocean heat uptake using observations of passive tracers in the ocean. He was graduated from Xiamen University, advised by Prof. Jianyu Hu (XMU), Dr. Xuebin Zhang (CSIRO) and Prof. John Church (UNSW).
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