SROCC: assessment of the ocean heat content change

doi:10.12006/j.issn.1673-1719.2019.237

Abstract

Abstract:

The greenhouse gases emitted by human activities into the atmosphere produce an Earth’s energy imbalance that leads to global heating. IPCC AR5 indicated that the ocean has taken up more than 90% of the excess heat in the climate system. It is virtually certain that the global ocean has warmed unabated since 1970, which is attributed to anthropogenic forcing. Since 1993, the rate of ocean warming has likely more than doubled. The deep ocean below 2000 m has likely warmed since 1992, especially in the Southern Ocean. The Southern Ocean accounted for 35%-43% of the total heat gain in the upper 2000 m global ocean between 1970 and 2017 (high confidence). Its share increased to 45%-62% between 2005 and 2017. It is virtually certain that the ocean will continue warming throughout the 21st century. By 2100, the top 2000 m of the ocean is projected to take up 5-7 times more heat under RCP8.5 (or 2-4 times more heat under RCP2.6) than the observed accumulated ocean heat uptake within 1970-2017. The thermal expansion due to ocean warming contributes to ~43% of the global sea level rise since 1993.

Key words: Special report on the ocean and cryosphere in a changing climate (SROCC), Ocean heat content, Accelerate, Southern Ocean, Sea level

CHENG Li-Jing. SROCC: assessment of the ocean heat content change[J]. Climate Change Research, 2020, 16(2): 172-181.

Figures/Tables 7

Fig. 1 Schematic illustration of key components and changes of the ocean and cryosphere, and their linkages in the Earth system through the movement of heat, water, and carbon [9] (the key changes found in SROCC are illustrated in circular icons)

Fig. 2 Time evolution of ocean subsurface temperature observations [9, 11] (a) Number of subsurface ocean temperature profiles per year by instrument type 1900-2017; (b) Percentage of data coverage for 3°×3° boxes over the global ocean area from 5 to 6000 m

Fig. 3 Time series of globally integrated upper 2000 m ocean heat content changes in ZJ[1] (relative to the 1986-2005 period average, as inferred from observations)[22]

Tab.1 The assessed rate of increase in ocean heat content in the two depth layers 0-700 m and 700-2000 m and their 5%-95% ranges[16] (Fluxes in W/m2 are averaged over the Earth’s entire surface area)

Fig. 4 Heat uptake by the top 700 m of the ocean, as determined by differences between the averages over two 5- or 20-year intervals converted to a heat flux into the ocean [16] (a) change between 1971-1990 and 1998-2017 as inferred from EN4 [33]; (b) the ensemble mean change in CMIP5 ESMs for the same time periods as in (a); (c) projected ensemble mean change in CMIP5 ESMs between 1986-2005 and 2081-2100 for the RCP8.5 forcing scenario (In panel (b) and (c), stippling indicates regions where the ensemble mean change is not significantly different from 0 at the 95% confidence level based on the models’ temporal variability); (d) change between 2005-2009 and 2013-2017 as inferred from observations by the SODA reanalysis product; (e) and (f) estimates of change in heat uptake as in (d) but from two individual realizations of the CCSM ESM (These two realizations are identical apart from their initial conditions)

Tab.2 Ocean heat content trend (0-2000 m depth) during 2005-2017 and 1970-2017 for the global ocean and Southern Ocean [17] (Ordinary Least Square method is used. Uncertainties denote the 90% confidence interval accounting for the reduction in the degrees of freedom implied by temporal correlations of residuals. Values in curved brackets are percentages of heat gain by the Southern Ocean relative to the global ocean. The mean proportion and its 5%-95% confidence interval (1.65 times standard deviation of individual estimates) are in the last column)

Fig. 5 (a) Zonally- and depth-integrated ocean heat content trends from EN4 datasets, for period 1982-2017; (b) Zonal-mean ocean potential temperature trend (shading) from EN4 for 1982-2017, with climatological ocean salinity in intervals of 0.15 (contours) [17,34]每个纬度的热含量变化/(ZJ/10a

References

[1]	Pörtner H O, Roberts D C, Masson-Delmotte V , et al. Summary for policymakers [M/OL]//IPCC. Special report on the ocean and cryosphere in a changing climate. 2019 [ 2019-10-09]. https://www.ipcc.ch/srocc/chapter/summary-for-policymakers/
[2]	Rhein M, Rintoul S R, Aoki S , et al. Observations: ocean [M] //IPCC. Climate change 2013: the physical science basis. Contribution of working groupΙto the fifth assessment report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York: Cambridge University Press, 2013
[3]	Trenberth K, Fasullo J, Balmaseda M . Earth’s energy imbalance[J]. Journal of Climate, 2014,27(9):3129-3144
[4]	Hansen J, Sato M, Kharecha P , et al. Earth’s energy imbalance and implications[J]. Atmospheric Chemistry and Physics, 2011,11:13421-13449
[5]	Cheng L, Zhu J, Abraham J , et al. 2018 continues record global ocean warming[J]. Advances in Atmospheric Sciences, 2019,36(3):249-252
[6]	IPCC. Climate change 2001: the scientific basis. Contribution of working groupΙto the third assessment report of the Intergovernmental Panel on Climate Change [M]. Cambridge, United Kingdom and New York: Cambridge University Press, 2001
[7]	IPCC. Climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the Intergovernmental Panel on Climate Change [M]. Cambridge, United Kingdom and New York: Cambridge University Press, 2007
[8]	IPCC. Climate change 2013: the physical science basis [M]. Cambridge, United Kingdom: Cambridge University Press, 2013
[9]	Abram N, Gattuso J P, Prakash A , et al. Framing and context of the report [M/OL]//IPCC. Special report on ocean and cryosphere in a changing climate. 2019 [ 2019-10-09]. https://www.ipcc.ch/srocc/chapter/chapter-1-framing-and-context-of-the-report/
[10]	Abraham J P, Baringer M, Bindoff N L , et al. A review of global ocean temperature observations: implications for ocean heat content estimates and climate change[J]. Reviews of Geophysics, 2013,51(3):450-483
[11]	Meyssignac B, Boyer T, Zhao Z , et al. Measuring global ocean heat content to estimate the Earth energy imbalance[J]. Frontiers in Marine Science, 2019,6(432)
[12]	Riser S C, Freeland H J, Roemmich D , et al. Fifteen years of ocean observations with the global Argo array[J]. Nature Climate Change, 2016,6(2):145-153
[13]	Cheng L, Abraham J, Goni G , et al. XBT science: assessment of instrumental biases and errors[J]. Bulletin of the American Meteorological Society, 2016,97(6):924-933
[14]	Durack P, Gleckler P J, Landerer F , et al. Quantifying underestimates of long-term upper-ocean warming[J]. Nature Climate Change, 2014,4:999-1005
[15]	Cheng L, Abraham J, Hausfather Z , et al. How fast are the oceans warming?[J]. Science, 2019,363(6423):128-129
[16]	Bindoff N L, Cheung W W L, Kairo J G, et al. Changing ocean, marine ecosystems, and dependent communities [M/OL]//IPCC. Special report on ocean and cryosphere in a changing climate. 2019 [ 2019-10-09]. https://www.ipcc.ch/srocc/chapter/chapter-5/
[17]	Meredith M S, Sommerkorn S, Cassotta S , et al. Polar regions [M/OL]//IPCC. Special report on ocean and cryosphere in a changing climate. 2019 [ 2019-10-09]. https://www.ipcc.ch/srocc/chapter/chapter-3-2/
[18]	Oppenheimer M, Glavovicc B, Hinkel J , et al. Sea level rise and implications for low lying islands, coasts and communities [M/OL]//IPCC. Special report on ocean and cryosphere in a changing climate. 2019 [ 2019-10-09]. https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/
[19]	Taylor K E, Stouffer R J, Meehl G A . An overview of CMIP5 and the experiment design[J]. Bulletin of the American Meteorological Society, 2012,93(4):485-498
[20]	Balmaseda M A, Hernandez F, Storto A , et al. The ocean reanalyses intercomparison project (ORA-IP)[J]. Journal of Operational Oceanography, 2015,8(S1):80-97
[21]	Carton J A, Chepurin G A, Chen L . SODA3: a new ocean climate reanalysis[J]. Journal of Climate, 2018,31(17):6967-6983
[22]	Cheng L, Trenberth K, Fasullo J , et al. Improved estimates of ocean heat content from 1960 to 2015[J]. Science Advances, 2017,3(3):e1601545
[23]	Domingues C M, Church J A, White N J , et al. Improved estimates of upper-ocean warming and multi-decadal sea-level rise[J]. Nature, 2008,453(7198):1090-U6
[24]	Ishii M, Fukuda Y, Hirahara S , et al. Accuracy of global upper ocean heat ccontent estimation expected from present observational data sets[J]. SOLA, 2017,13:163-167
[25]	Talley L D, Feely R A, Sloyan B M , et al. Changes in ocean heat, carbon content, and ventilation: a review of the first decade of GO-SHIP global repeat hydrography[J]. Annual Review of Marine Science, 2016,8(1):185-215
[26]	Purkey S, Johnson G . Warming of global abyssal and deep southern ocean waters between the 1990s and 2000s: contributions to global heat and sea level rise budgets[J]. Journal of Climate, 2010,23(23):6336-6351
[27]	Desbruyères D, Mcdonagh E L, King B A , et al. Global and full-depth ocean temperature trends during the early twenty-first century from Argo and repeat hydrography[J]. Journal of Climate, 2017,30(6):1985-1997
[28]	Bindoff N L, Stott P A, Achutarao K M , et al. Detection and attribution of climate change: from global to regional [M] //IPCC. Climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York: Cambridge University Press, 2013
[29]	Gregory J M E A. Climate models without pre-industrial volcanic forcing underestimate historical ocean thermal expansion[J]. Geophysical Research Letters, 2013,40:1-5
[30]	Cheng L, Trenberth K E, Palmer M D , et al. Observed and simulated full-depth ocean heat-content changes for 1970-2005[J]. Ocean Science, 2016,12(4):925-935
[31]	Gleckler P J, Durack P J, Stouffer R J , et al. Industrial-era global ocean heat uptake doubles in recent decades[J]. Nature Climate Change, 2016,6(4):394-398
[32]	Collins M, Knutti R, Arblaster J , et al. Long-term climate change: projections, commitments and irreversibility [M] //IPCC. Climate change 2013: the physical science basis: contribution of working group I to the fifth assessment report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press, 2013: 1029-1136
[33]	Good S A, Martin M J, Rayner N A . EN4: quality controlled ocean temperature and salinity profiles and monthly objective analyses with uncertainty estimates[J]. Journal of Geophysical Research Oceans, 2013,118(12):6704-6716
[34]	Armour K C, Marshall J, Scott J R , et al. Southern Ocean warming delayed by circumpolar upwelling and equatorward transport[J]. Nature Geoscience, 2016,9:549
[35]	Shi J R, Xie S P, Talley L D . Evolving relative importance of the Southern Ocean and North Atlantic in anthropogenic ocean heat uptake[J]. Journal of Climate, 2018,31(18):7459-7479
[36]	Swart N C, Gille S T, Fyfe J C , et al. Recent Southern Ocean warming and freshening driven by greenhouse gas emissions and ozone depletion[J]. Nature Geoscience, 2018,11(11):836-841
[37]	Frölicher T L, Sarmiento J L, Paynter D J , et al. Dominance of the Southern Ocean in anthropogenic carbon and heat uptake in CMIP5 models[J]. Journal of Climate, 2014,28(2):862-886
[38]	Purkey S G, Johnson G C . Global contraction of Antarctic bottom water between the 1980s and 2000s[J]. Journal of Climate, 2012,25(17):5830-5844
[39]	Gao L, Rintoul S R, Yu W . Recent wind-driven change in Subantarctic Mode Water and its impact on ocean heat storage[J]. Nature Climate Change, 2017,8(1)
[40]	Irving D B, Wijffels S, Church J A . Anthropogenic aerosols, greenhouse gases, and the uptake, transport, and storage of excess heat in the climate system[J]. Geophysical Research Letters, 2019,46(9):4894-4903
[41]	Hu D, Wu L, Cai W , et al. Pacific western boundary currents and their roles in climate[J]. Nature, 2015,522:299