Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action

Abstract

Sea-level rise is a major consequence of climate change that will continue long after emissions of greenhouse gases have stopped. The 2015 Paris Agreement aims at reducing climate-related risks by reducing greenhouse gas emissions to net zero and limiting global-mean temperature increase. Here we quantify the effect of these constraints on global sea-level rise until 2300, including Antarctic ice-sheet instabilities. We estimate median sea-level rise between 0.7 and 1.2 m, if net-zero greenhouse gas emissions are sustained until 2300, varying with the pathway of emissions during this century. Temperature stabilization below 2 °C is insufficient to hold median sea-level rise until 2300 below 1.5 m. We find that each 5-year delay in near-term peaking of CO₂ emissions increases median year 2300 sea-level rise estimates by ca. 0.2 m, and extreme sea-level rise estimates at the 95th percentile by up to 1 m. Our results underline the importance of near-term mitigation action for limiting long-term sea-level rise risks.

Fig. 1

CO₂ emissions and respective global-mean temperature and sea-level responses. Emission scenarios based on RCP2.6 with CO₂ emissions from fossil-fuel use and industry linearly continued with the present day rate until peak year. CO₂ emissions decline by 0.3, 0.5, and 0.7 GtC yr⁻² thereafter until net-zero CO₂ a or net-zero greenhouse gas emissions d are reached. Scenarios that do not hold warming to below 2 °C with at least 66% chance are masked gray. b, e Global-mean temperature responses to emissions scenarios a, d in °C above pre-industrial levels. c, f Global-mean sea-level rise relative to the year 2000. Shading refers to the central 66th percentile range per scenario in b, e and to the central 90th percentile range in c, f

Fig. 2

Response of the sea-level contributors to net-zero CO₂ scenarios. Time series of the sea-level responses of thermal expansion a, mountain glaciers b, Greenland mass balance c, and Antarctic mass balance d. Sea-level rise is in cm and relative to the year 2000. Colors refer to peak years as in Fig. 1. Shadings show the central 90th percentile range

Fig. 3

Response of the sea-level contributors to net-zero GHG scenarios. Time series of the sea-level responses of thermal expansion a, mountain glaciers b, Greenland mass balance c, and Antarctic mass balance d. Sea-level rise is in cm and relative to the year 2000. Colors refer to peak years as in Fig. 1. Shadings show the central 90th percentile range

Fig. 4

Characteristics of emission pathways versus sea-level rise in 2300. CO₂ emission levels in 2030 a, d and 2050 b, e for net-zero CO₂ (half-filled markers) and net-zero GHG (filled markers) scenarios versus median a, b and 95th percentile d, e sea-level rise in 2300. The vertical black line shows CO₂ emissions in 2015. c, f CO₂ emission peak year versus median c and 95th percentile f sea-level rise in 2300 with same markers as in a–d and linear fits for scenarios with the same decarbonization rate as gray lines. Rate in legend refers to the rate of emissions reductions after the emissions peak in GtC yr⁻²

Fig. 5

Sea-level rise in 2300 and temperature overshoot above 1.5 °C. a Median sea-level rise versus the temporal overshoot in years. b Median sea-level rise versus the time integral of the temperature overshoot. Half-filled markers indicate net-zero CO₂ scenarios, filled markers net-zero GHG scenarios. Gray crosses show net-zero GHG scenarios that do not comply with the 2 °C target of the Paris Agreement. Rate in legend refers to the rate of emissions reductions after the emissions peak in GtC yr⁻². The grouping of net-zero CO₂ scenarios exceeding 1.5 °C in the upper-right corner of a reflects the length of our simulations and is of limited significance