scholarly journals Control of transient climate response and associated sea level rise by deep-ocean mixing

2020 ◽  
Vol 15 (9) ◽  
pp. 094001 ◽  
Author(s):  
Michio Watanabe ◽  
Hiroaki Tatebe ◽  
Tatsuo Suzuki ◽  
Kaoru Tachiiri
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Deep Ocean ◽  
Ocean Mixing ◽  
Climate Response ◽  
Transient Climate Response

scholarly journals Irreversible ocean thermal expansion under negative CO<sub>2</sub> emissions

2017 ◽  
Author(s):  
Dana Ehlert ◽  
Kirsten Zickfeld
Keyword(s):  
Thermal Expansion ◽  
Sea Level Rise ◽  
Sea Level ◽  
Climate Model ◽  
Deep Ocean ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Ocean Mixing ◽  
Industrial Concentration ◽  
Ocean Heat Uptake

Abstract. In the Paris Agreement in 2015 countries agreed on holding global mean surface air warming well below 2 °C but the emission reduction pledges under that agreement are not ambitious enough to meet this target. Therefore, the question arises whether restoring temperature to this target after exceeding it by artificially removing CO2 from the atmosphere is possible. One important aspect regards the reversibility of ocean heat uptake and the associated sea level rise, which have very long (centennial to millennial) response time scales. In this study the response of sea level rise due to thermal expansion (TSLR) to a 1 % yearly increase of atmospheric CO2 up to a quadrupling of the pre-industrial concentration followed by a 1 % yearly decline back to the pre-industrial CO2 concentration is examined using the University of Victoria Earth System Climate Model (UVic ESCM). We find that TSLR continues for several decades after atmospheric CO2 starts to decline and that sea level does not return to pre-industrial levels for over thousand years after atmospheric CO2 is restored to pre-industrial concentrations. This finding is independent of the strength of vertical sub-grid scale ocean mixing implemented in the model. Furthermore, TSLR rises faster than it declines in response to a symmetric rise and decline in atmospheric CO2 concentration partly because the deep ocean continues to warm for centuries after atmospheric CO2 returns to the pre-industrial concentration. Both TSLR rise and decline rate increase with increasing vertical ocean mixing. Exceptions from this behaviour arise if the overturning circulations in the North Atlantic and Southern Ocean intensify beyond pre-industrial levels in model versions with lower vertical mixing, which leads to rapid cooling of the deep ocean.

scholarly journals Irreversible ocean thermal expansion under carbon dioxide removal

2018 ◽  
Vol 9 (1) ◽  
pp. 197-210 ◽  
Author(s):  
Dana Ehlert ◽  
Kirsten Zickfeld
Keyword(s):  
Thermal Expansion ◽  
Sea Level Rise ◽  
Sea Level ◽  
Deep Ocean ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Ocean Mixing ◽  
Industrial Concentration ◽  
Ocean Heat Uptake ◽  
Global Mean

Abstract. In the Paris Agreement in 2015 countries agreed on holding global mean surface air warming to well below 2 °C above pre-industrial levels, but the emission reduction pledges under that agreement are not ambitious enough to meet this target. Therefore, the question arises of whether restoring global warming to this target after exceeding it by artificially removing CO2 from the atmosphere is possible. One important aspect is the reversibility of ocean heat uptake and associated sea level rise, which have very long (centennial to millennial) response timescales. In this study the response of sea level rise due to thermal expansion to a 1 % yearly increase of atmospheric CO2 up to a quadrupling of the pre-industrial concentration followed by a 1 % yearly decline back to the pre-industrial CO2 concentration is examined using the University of Victoria Earth System Climate Model (UVic ESCM). We find that global mean thermosteric sea level (GMTSL) continues to rise for several decades after atmospheric CO2 starts to decline and does not return to pre-industrial levels for over 1000 years after atmospheric CO2 is restored to the pre-industrial concentration. This finding is independent of the strength of vertical sub-grid-scale ocean mixing implemented in the model. Furthermore, GMTSL rises faster than it declines in response to a symmetric rise and decline in atmospheric CO2 concentration partly because the deep ocean continues to warm for centuries after atmospheric CO2 returns to the pre-industrial concentration. Both GMTSL rise and decline rates increase with increasing vertical ocean mixing. Exceptions from this behaviour arise if the overturning circulations in the North Atlantic and Southern Ocean intensify beyond pre-industrial levels in model versions with lower vertical mixing, which leads to rapid cooling of the deep ocean.

scholarly journals The inconstancy of the transient climate response parameter under increasing CO 2

2015 ◽  
Vol 373 (2054) ◽  
pp. 20140417 ◽  
Author(s):  
J. M. Gregory ◽  
T. Andrews ◽  
P. Good
Keyword(s):  
Radiative Forcing ◽  
Coupled Model ◽  
Surface Air Temperature ◽  
Deep Ocean ◽  
Climate Feedback ◽  
Climate Response ◽  
Ocean Heat Uptake ◽  
Transient Climate Response ◽  
Feedback Parameter ◽  
Response Parameter

In the Coupled Model Intercomparison Project Phase 5 (CMIP5), the model-mean increase in global mean surface air temperature T under the 1pctCO2 scenario (atmospheric CO 2 increasing at 1% yr −1 ) during the second doubling of CO 2 is 40% larger than the transient climate response (TCR), i.e. the increase in T during the first doubling. We identify four possible contributory effects. First, the surface climate system loses heat less readily into the ocean beneath as the latter warms. The model spread in the thermal coupling between the upper and deep ocean largely explains the model spread in ocean heat uptake efficiency. Second, CO 2 radiative forcing may rise more rapidly than logarithmically with CO 2 concentration. Third, the climate feedback parameter may decline as the CO 2 concentration rises. With CMIP5 data, we cannot distinguish the second and third possibilities. Fourth, the climate feedback parameter declines as time passes or T rises; in 1pctCO2, this effect is less important than the others. We find that T projected for the end of the twenty-first century correlates more highly with T at the time of quadrupled CO 2 in 1pctCO2 than with the TCR, and we suggest that the TCR may be underestimated from observed climate change.

scholarly journals Polar Region Bathymetry: Critical Knowledge for the Prediction of Global Sea Level Rise

2022 ◽  
Vol 8 ◽  
Author(s):  
Martin Jakobsson ◽  
Larry A. Mayer
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Deep Ocean ◽  
The Arctic ◽  
Polar Regions ◽  
Ice Dynamics ◽  
Critical Knowledge ◽  
Subsurface Waters ◽  
Global Sea Level ◽  
The Many

The ocean and the marine parts of the cryosphere interact directly with, and are affected by, the seafloor and its primary properties of depth (bathymetry) and shape (morphology) in many ways. Bottom currents are largely constrained by undersea terrain with consequences for both regional and global heat transport. Deep ocean mixing is controlled by seafloor roughness, and the bathymetry directly influences where marine outlet glaciers are susceptible to the inflow relatively warm subsurface waters - an issue of great importance for ice-sheet discharge, i.e., the loss of mass from calving and undersea melting. Mass loss from glaciers and the Greenland and Antarctic ice sheets, is among the primary drivers of global sea-level rise, together now contributing more to sea-level rise than the thermal expansion of the ocean. Recent research suggests that the upper bounds of predicted sea-level rise by the year 2100 under the scenarios presented in IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate (SROCCC) likely are conservative because of the many unknowns regarding ice dynamics. In this paper we highlight the poorly mapped seafloor in the Polar regions as a critical knowledge gap that needs to be filled to move marine cryosphere science forward and produce improved understanding of the factors impacting ice-discharge and, with that, improved predictions of, among other things, global sea-level. We analyze the bathymetric data coverage in the Arctic Ocean specifically and use the results to discuss challenges that must be overcome to map the most remotely located areas in the Polar regions in general.

scholarly journals The transient sensitivity of sea level rise

2020 ◽  
Author(s):  
Aslak Grinsted ◽  
Jens Hesselbjerg Christensen
Keyword(s):  
Carbon Dioxide ◽  
Sea Level Rise ◽  
Sea Level ◽  
Carbon Dioxide Emissions ◽  
Climate Models ◽  
Carbon Dioxide Emission ◽  
Rate Of Change ◽  
Intergovernmental Panel ◽  
Transient Climate Response ◽  
Global Mean

Abstract. Recent assessments from the Intergovernmental Panel on Climate Change implies that global mean sea level is unlikely to rise more than about 1.1 m within this century, but with further increase beyond 2100, even within the most intensive future anthropogenic carbon dioxide emission scenarios. However, some studies conclude that considerably greater sea level rise could be realized, and experts assign a substantially higher likelihood of such a future. To understand this discrepancy, it would be useful to have scenario independent metrics that can be compared between different approaches. The concept of a transient climate response has proven to be useful to compare the response of climate models. Here, we introduce a similar metric for sea level science. By analyzing mean rate of change in sea level (not sea level itself), we identify a near linear relationship with global mean surface temperature (and therefore accumulated carbon dioxide emissions) in both model projections, and in observations on a century time scale. This motivates us to define the Transient Sea Level Sensitivity as the increase in the sea level rate associated with a given warming in units of m/century/K. We find that model projections fall below extrapolation based on recent observational records. This comparison indicates that the likely upper level of sea level projections in recent IPCC reports would be too low.

scholarly journals The Effect of Ocean Ventilation on the Transient Climate Response to Emissions

2019 ◽  
Vol 32 (16) ◽  
pp. 5085-5105 ◽  
Author(s):  
Anna Katavouta ◽  
Richard G. Williams ◽  
Philip Goodwin
Keyword(s):  
Southern Ocean ◽  
Time Scales ◽  
Mixed Layer ◽  
Carbon Emissions ◽  
Deep Ocean ◽  
Climate Response ◽  
Transient Climate Response ◽  
Surface Warming ◽  
Ocean Ventilation ◽  
Meridional Overturning

Abstract The surface warming response to carbon emissions is affected by how the ocean sequesters excess heat and carbon supplied to the climate system. This ocean uptake involves the ventilation mechanism, where heat and carbon are taken up by the mixed layer and transferred to the thermocline and deep ocean. The effect of ocean ventilation on the surface warming response to carbon emissions is explored using simplified conceptual models of the atmosphere and ocean with and without explicit representation of the meridional overturning. Sensitivity experiments are conducted to investigate the effects of (i) mixed layer thickness, (ii) rate of ventilation of the ocean interior, (iii) strength of the meridional overturning, and (iv) extent of subduction in the Southern Ocean. Our diagnostics focus on a climate metric, the transient climate response to carbon emissions (TCRE), defined by the ratio of surface warming to the cumulative carbon emissions, which may be expressed in terms of separate thermal and carbon contributions. The variability in the thermal contribution due to changes in ocean ventilation dominates the variability in the TCRE on time scales from years to centuries, while that of the carbon contribution dominates on time scales from centuries to millennia. These ventilated controls are primarily from changes in the mixed layer thickness on decadal time scales, and in the rate of ventilated transfer from the mixed layer to the thermocline and deep ocean on centennial and millennial time scales, which is itself affected by the strength of the meridional overturning and extent of subduction in the Southern Ocean.

Anthropogenic modification of the oceans

2011 ◽  
Vol 369 (1938) ◽  
pp. 887-908 ◽  
Author(s):  
Toby Tyrrell
Keyword(s):  
Global Warming ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ocean Circulation ◽  
Human Activities ◽  
Sea Water ◽  
Deep Ocean ◽  
Considerable Reduction ◽  
Surface Ocean ◽  
And Sea Level

Human activities are altering the ocean in many different ways. The surface ocean is warming and, as a result, it is becoming more stratified and sea level is rising. There is no clear evidence yet of a slowing in ocean circulation, although this is predicted for the future. As anthropogenic CO 2 permeates into the ocean, it is making sea water more acidic, to the detriment of surface corals and probably many other calcifiers. Once acidification reaches the deep ocean, it will become more corrosive to CaCO 3 , leading to a considerable reduction in the amount of CaCO 3 accumulating on the deep seafloor. There will be a several thousand-year-long interruption to CaCO 3 sedimentation at many points on the seafloor. A curious feedback in the ocean, carbonate compensation, makes it more likely that global warming and sea-level rise will continue for many millennia after CO 2 emissions cease.

Glacial Contributions to 21st Century Sea Level Rise

Eos ◽  
2020 ◽  
Vol 101 ◽  
Author(s):  
Kate Wheeling
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
21St Century ◽  
Mass Change ◽  
Sources Of Uncertainty

Researchers identify the main sources of uncertainty in projections of global glacier mass change, which is expected to add about 8–16 centimeters to sea level, through this century.

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