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Earth System Dynamics An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/esd-2017-105
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
27 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth System Dynamics (ESD).
Climate, ocean circulation, and sea level changes under stabilization and overshoot pathways to 1.5 K warming
Jaime B. Palter1, Thomas L. Frölicher2,3, David Paynter4, and Jasmin G. John4 1University of Rhode Island, Graduate School of Oceanography
2Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
3Oeschger Centre for Climate Change Research, University of Bern, Switzerland
4National Oceanic and Atmospheric Administration, Geophysical Fluid Dynamics Laboratory
Abstract. The Paris Climate Agreement has initiated a scientific debate on the role that carbon removal – or net negative emissions – might play in achieving less than 1.5 K of global mean surface warming by 2100. Here, we probe the sensitivity of a comprehensive Earth System Model to three different atmospheric CO2 concentration pathways, two of which arrive at 1.5 K of warming in 2100 by very different pathways. We run five ensemble members of each of these simulations: 1) a standard Representative Concentration Pathway (RCP4.5) scenario, which produces 2 K of surface warming by 2100 in our model; 2) a stabilization pathway in which atmospheric CO2 concentration never exceeds 440 ppm and the global mean temperature rise is approximately 1.5 K by 2100; and 3) an overshoot pathway that passes through 2 K of warming at mid-century, before ramping down atmospheric CO2 concentrations, as if using carbon removal, to end at 1.5 K of warming at 2100. Although the global mean surface temperature change in response to the overshoot pathway is similar to the stabilization pathway in 2100, this similarity belies several important differences in other climate metrics, such as warming over land masses, the strength of the Atlantic Meridional Overturning Circulation, sea ice coverage, and the global mean sea level change and its regional expressions. In 2100, the overshoot ensemble is closer to RCP4.5 than the ‘stabilization’ ensemble with respect to global steric sea level rise and the strength of the Atlantic Meridional Overturning Circulation (AMOC). There is strong ocean surface cooling in the North Atlantic and Southern Ocean in response to overshoot forcing due to perturbations in the ocean circulation. Thus, overshoot forcing in this model reduces the rate of sea ice loss in the Labrador, Nordic, Ross, and Weddell Seas relative to the stabilized pathway, suggesting a negative radiative feedback in response to the early rapid warming. Finally, the ocean perturbation in response to warming leads to strong pathway-dependence of sea level rise in northern North American cities, with overshoot forcing producing up to 10 cm of additional sea level rise by 2100 relative to stabilization forcing.

Citation: Palter, J. B., Frölicher, T. L., Paynter, D., and John, J. G.: Climate, ocean circulation, and sea level changes under stabilization and overshoot pathways to 1.5 K warming, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-105, in review, 2017.
Jaime B. Palter et al.
Jaime B. Palter et al.
Jaime B. Palter et al.

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Short summary
Limiting global warming to 1.5 °C may require carbon removal from the atmosphere. We explore how the climate system differs when we achieve the 1.5 °C limit by rapid emissions reductions versus when we overshoot this limit, hitting 2 °C at mid-century before removing CO2 from the atmosphere. Using a model, we show that sea level, ocean acidification, regional warming, and ocean circulation are very different under the overshoot pathway at 2100, despite hitting the 1.5 °C target for surface warming.
Limiting global warming to 1.5 °C may require carbon removal from the atmosphere. We explore...
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