Earth’s Future
21st Century Sea-Level Rise in Line with the Paris Accord
Luke P. Jackson
1
, Aslak Grinsted
2
, and Svetlana Jevrejeva
3
1
Programme for Economic Modelling, Nuffield College, Oxford, UK,
2
Centre for Ice and Climate, Niels Bohr Institute,
University of Copenhagen, Copenhagen, Denmark,
3
National Oceanography Centre, Liverpool, UK
Abstract
As global average sea-level rises in the early part of this century there is great interest in
how much global and local sea level will change in the forthcoming decades. The Paris Climate Agree-
ment’s proposed temperature thresholds of 1.5
∘
Cand2
∘
C have directed the research community to ask
what differences occur in the climate system for these two states. We have developed a novel approach
to combine climate model outputs that follow specific temperature pathways to make probabilistic pro-
jections of sea-level in a 1.5
∘
Cand2
∘
C world. We find median global sea-level (GSL) projections for 1.5
∘
C
and 2
∘
C temperature pathways of 44 and 50 cm, respectively. The 90% uncertainty ranges (5%–95%) are
both around 48 cm by 2100. In addition, we take an alternative approach to estimate the contribution
from ice sheets by using a semi-empirical GSL model. Here we find median projections of 58 and 68 cm for
1.5
∘
Cand2
∘
C temperature pathways. The 90% uncertainty ranges are 67 and 82 cm respectively. Regional
projections show similar patterns for both temperature pathways, though differences vary between the
median projections (2–10 cm) and 95th percentile (5–20 cm) for the bulk of oceans using process-based
approach and 10–15 cm (median) and 15–25 cm (95th percentile) using the semi-empirical approach.
Plain Language Summary
The sea level you experience at the coast can be estimated by the
sum of contributions from ocean expansion, currents, ice melt from glaciers and ice sheets, land-water
extraction/damming, and land motion. How sea level changes depends strongly on where you are
because each contribution has a unique pattern. We use knowledge of these changes to make projections
about future sea-level rise. We estimate how much sea-level could change if societies achieve either of the
Paris Climate Agreement’s temperature targets by 2100. If we reach 1.5
∘
Cor2.0
∘
C by 2100, GSL should
rise around 44–50 cm, respectively. Using a slightly different method we find the global rise could be
58–68 cm. An incomplete picture of the sea-level components means that estimates could be out by up
to 80 cm, though all projections show a sea-level rise of at least 20 cm.
1. Introduction
The Paris Climate Agreement (United Nations [UN], 2015a) aims to hold the rise in global average tempera-
tures to “well below 2
∘
C above preindustrial levels and to pursue efforts to limit the temperature increase
to 1.5
∘
C above preindustrial levels.” The agreement was signed by 195 countries and ratified by 170, equiv-
alent to 87.9% of global emissions (Climate Analytics, 2017). While this outcome is highly encouraging, the
process required to achieve deep and rapid emission reduction remains extremely challenging (Rogelj et al.,
2016). A key question posed to the research community is the difference between the climate systems for
these two temperature scenarios. At present, temperature pathways are an output of climate models for
specific emissions scenarios rather than being the parameter under control.
While the atmospheric community have developed intercomparison projects to explore the impact
of a Paris-like agreement upon, for example temperature and precipitation extremes (e.g., Mitchell
et al., 2017), such intercomparison projects have not been made by the oceanographic community.
This leaves the sea-level community needing to make the best of currently available data and meth-
ods. Two recent approaches aimed at overcoming this problem use idealized temperature pathways
to drive a simple semi-empirical global sea-level (GSL) model (Bittermann et al., 2017), and use a
reduced complexity carbon cycle—climate model to derive temperature ensembles that are used to
drive a temperature scaled regional sea-level model (Schleussner et al., 2016). Rasmussen et al. (2017)
RESEARCH ARTICLE
10.1002/2017EF000688
Key Points:
• We use a novel method to make
sea-level projections for global
temperature pathways
• Median global sea-level projections
for 1.5 and 2 degrees C in 2100 are 44
cm and 50 cm respectively
• Using a semi-empirical method,
median global projections for 1.5 and
2 degrees C in 2100 rise to 58 cm and
68 cm
Supporting Information:
• Supporting Information S1
Correspondence to:
L. P. Jackson, luke.jackson@economics.
ox.ac.uk
Citation:
Jackson, L. P., Grinsted, A., & Jevrejeva,
S. (2018). 21st Century Sea-Level Rise in
Line with the Paris Accord, Earth’s
Future, 6, 213 –229, https://doi.org/10
.1002/2017EF000688
Received 20 SEP 2017
Accepted 15 JAN 2018
Accepted article online 24 JAN 2018
Published online 9 FEB 2018
© 2018 The Authors.
This is an open access article under
the terms of the Creative Commons
Attribution License, which permits use,
distribution and reproduction in any
medium, provided the original work is
properly cited.
JACKSON ET AL. 213
@Phil_Robichaud
@deepthiw
@JoseServera