Abstract
More than 90% of the Earth’s energy imbalance is stored by the ocean. While previous studies have shown that changes in the ocean warming are detectable and distinct from internal variability of the climate system, an estimate of separate contributions by natural and individual anthropogenic forcings (such as greenhouse gases and aerosols) remains outstanding. Here we investigate anthropogenic and greenhouse-gas contributions to past ocean warming, and estimate their contributions to future sea level rise by the year 2100. By applying detection and attribution framework (regularized optimal fingerprinting), we show that ocean warming in the historical period is detectable and attributable to contributions from the aggregate anthropogenic forcing as well as greenhouse gas forcing alone. We also discuss the role of natural forcing on the ocean volume-averaged temperature and examine the impact of volcanic activity from the three main volcanoes occurring in the historical period 1955–2012. Our results suggest that estimated anthropogenic and greenhouse-gas contributions to ocean warming are consistent with observations, and observationally-constrained future thermosteric sea level rise projections support the central and lower part of the multi-model mean projection range distribution.
Highlights
The excess energy in the climate system resulting from the net energy imbalance at the top of the atmosphere is accumulated in the ocean, resulting in its warming
An earlier study by Slangen et al (2014) derived the anthropogenic scaling factor bANT of 1.08 ± 0.13 (±2 σ) by inferring sea level rise from interpolated observations of the ocean heat content prior to detection and attribution analysis performed directly on the sea level time-series. This is broadly consistent with our bANT estimates 0.86 (5%–95% range of [0.69, 1.05]; figure S5; supplementary table S2) and similar to our values of bGHG of 0.91 (5%–95% range of [0.67, 1.17]), since greenhouse-gas only forcing (GHG) forcing is the dominant component of the anthropogenic forcing (ANT)
Previous detection and attribution studies primarily focused on separating natural signal and the forced responses due to all anthropogenic forcings
Summary
, Aurélien Ribes2 and Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Keywords: ocean warming, thermosteric sea level, detection and attribution, climate change, Earth system modelling
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